# On the stiffness fairytale...



## Pirx (Aug 9, 2009)

This is somewhat of an old topic, and I think by now many of us understand that the still ongoing obsession with frame stiffness, in the form of "lateral stiffness", "stiff bottom brackets", etc., etc., is nothing but marketing BS. Yet, just about _every single article_ you see that presents a "review" of some new bicycle, and certainly _every single manufacturer blurb_ about the newest bike from manufacturer X still continues perpetuating this idiocy.

On the other hand, from the physics of bicycles it is entirely clear that frame flex, at the kind of level any halfway realistic, existing road bike will show, has almost exactly zero effect on the efficiency of "power transfer" (whatever that may mean; we note in passing that nobody ever bothers to define this term, and there is certainly not a single test or experiment of any kind that would demonstrate the relevance of this quantity). I have therefore argued for a long time that, if there is any effect of frame stiffness on performance at all, it would have to be sought in the biomechanical efficiency of the rider-bicycle system. However, a priori there is no reason to assume that this system will perform either better or worse using a stiffer frame. As a consequence, it may well be that some riders do better on more flexible frames, and some others may prefer stiffer ones. Bottom line: Nobody knows, and all the rest is nothing but clueless babble.

The reason I am repeating the above well-known truths is that I just happened to stumble over an older post in the _Bicycle Quarterly and Compass Bicycles_ blog, which in fact quotes a few pieces of evidence confirming what I've been saying for years. Here is a pertinent quote:



> In recent years, it has become clear that many riders perform better on flexible frames, apparently because it allows them to apply their power more efficiently. Many riders and builders extol the virtues of a “lively” frame made from flexible tubing. When we tested different frame tubing in a double-blind test (Bicycle Quarterly Vol. 6, No. 4), we found that two of three riders preferred the most flexible frame both for constant efforts and for all-out sprints. (The third rider could not tell the – very small – differences between the frames in our test.)


The penultimate paragraph in that piece is also worth quoting in full:


> Of course, the real story is more complex. There is more to bicycle performance than overall frame stiffness. Frames can be too flexible for a given rider and application. Some riders may even prefer very stiff frames. However, it is clear that the old mantra of stiffer = more performance is not true for most riders


Amen to that.

Here's my proposal: Can we please lay this BS of the superiority of the stiff frame to rest? Better aerodynamics, yes, lower weight, yes, these things can help increase performance. Frame stiffness? Completely and utterly irrelevant.


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## robt57 (Jul 23, 2011)

Pirx said:


> Here's my proposal: Can we please lay this BS of the superiority of the stiff frame to rest? Better aerodynamics, yes, lower weight, yes, these things can help increase performance. Frame stiffness? Completely and utterly irrelevant.


Go find a 1995 Litespeed Catalyst and do some sprinting on it, especially if you ride a large size and weigh 200 lbs with 28 in upper legs and report back.

On the flip side, the 58CM SL4 Roubiax lasted 7 months of me putting CGR posts and 27mm Pave tires before i sold it off for being too unforgiving IMO. 

So lets assume it is not BS and that the big grey area between too stiff and too flexy is the place riders may find themselves falling comfortably.


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## tvad (Aug 31, 2003)

My own non-empirical experience going from a Ti Litespeed Tuscany to a stiff carbon Cervelo R3 tells me stiffness does matter in performance (improved acceleration and faster average speed). The difference was immediately noticeable.


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## Pirx (Aug 9, 2009)

robt57 said:


> Go find a 1995 Litespeed Catalyst and do some sprinting on it, especially if you ride a large size and weigh 200 lbs with 28 in upper legs and report back.


That test has been done, with some 1983 steel steed (Pinarello) versus a modern carbon bike (2009 Lapierre). Result, in a nutshell: No difference.



tvad said:


> My own non-empirical experience going from a Ti Litespeed Tuscany to a stiff carbon Cervelo R3 tells me stiffness does matter in performance (improved acceleration and faster average speed). The difference was immediately noticeable.


The difference was all in your head, at least the difference caused by increased stiffness. Stiffness has no measurable effect on acceleration, and no effect on average speed. Your Cervelo is lighter, hence the better acceleration, and much more aerodynamic, thus higher average speed. Nothing to do with stiffness.


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## Manning (Jul 8, 2010)

I'll just leave this here......

Thoughts on science & perception - Slowtwitch.com


and 

Road to Roubaix, Part 1 | SILCA

then there's part 2 and 3


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## tvad (Aug 31, 2003)

Pirx said:


> The difference was all in your head, at least the difference caused by increased stiffness.


No, it wasn't in my head. But kudos for your persistence.


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## GlobalGuy (Jun 9, 2015)

I’m neither a physics or bicycle expert. Nor have I ever stayed at a Holliday Express. So…a question:

When the rider puts down power to the pedals is he not transferring kinetic energy? If that is so then isn’t it accurate that the more the bike frame flexes the greater amount of "loss" of that kinetic energy during that flexion? If that is true than the less the frame flexes the greater the amount of kinetic energy that goes somewhere else? If that is true, where does it go?

Just asking.


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## Pirx (Aug 9, 2009)

tvad said:


> No, it wasn't in my head. But kudos for your persistence.


Well, yeah, I'm strange this way I know. I'm one of those weird people who thinks that the laws of physics do hold. There are others, like you, who feel their imagination trumps physics. That's what is indeed required to believe in the fairytales of the miraculous benefits of frame stiffness.



GlobalGuy said:


> When the rider puts down power to the pedals is he not transferring kinetic energy?


No, what he is transferring is force, which gets converted to torque. At the rear wheel the torque gets converted back into a propulsive force. If that propulsive force is not balanced by an equal and opposite resistive force, acceleration results, which increases the kinetic energy of the rider-bicycle system, yes.



GlobalGuy said:


> If that is so then isn’t it accurate that the more the bike frame flexes the greater amount of "loss" of that kinetic energy during that flexion?


Since this is not so, your antecedent is wrong, too. I'll just leave it at that.



GlobalGuy said:


> If that is true, where does it go?


If some of the energy input by the rider is used to temporarily flex the frame, once the frame un-flexes the energy is returned. All of it. No energy is lost. None. At. All.


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## Cinelli 82220 (Dec 2, 2010)

Pirx said:


> I'm one of those weird people who thinks that the laws of physics do hold.





> No energy is lost. None. At. All.


Both these assertions cannot be true. You can believe one but not the other.


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## Pirx (Aug 9, 2009)

Cinelli 82220 said:


> Both these assertions cannot be true. You can believe one but not the other.


How so?

P.S.: Do you understand the meaning of the term "elastic deformation"?


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## dcgriz (Feb 13, 2011)

I'll say a good bit of it goes in jolting the bike-rider up and down. The claim BQ is making about "planing" is based on progressively stiffer tubes from a light TT, stiffer DT and stiff CS. The concept is stiff chain stays to efficiently transfer your pedaling energy to the ground and flexier top frame to smooth out the movement oscillation and help the rider pedal stroke sync with the bike.


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## Pirx (Aug 9, 2009)

dcgriz said:


> The concept is stiff chain stays to efficiently transfer your pedaling energy to the ground and flexier top frame to smooth out the movement oscillation and help the rider pedal stroke sync with the bike.


Like I said, a fairytale, and nothing but a fairytale. 

I will note that it is indeed possible to make the vague concepts you are referring to precise, and test them. It is telling that nobody has ever performed such a test. All the more so given the amount of effort the cycling industry presumably invests into developing ever stiffer frames. Wouldn't you think that, before you invest into a certain characteristic, that you might test whether that characteristic is indeed beneficial? Of course, in this case, the answer is simple, but it's not in the physics but in the marketing, to a scientifically illiterate public.


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## robt57 (Jul 23, 2011)

Pirx said:


> If some of the energy input by the rider is used to temporarily flex the frame, once the frame un-flexes the energy is returned. All of it. No energy is lost. None. At. All.


Except some is returned back into the leg muscles instead of having been already put to the wheel.

I can do 80 miles hard on my Addict, and 50 would bring me closer to being tired and slowing in the last 10 that on the 2005 flexy [albeit very comfortable] Roubaix.

Obviously my imagination...


I had enough, out. Should have known better than to take the troll bait anyway..
Even if the troll has rep out the ying yang.


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## tvad (Aug 31, 2003)

robt57 said:


> Should have known better than to take the troll bait anyway..


The take-away of the thread.


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## goodboyr (Apr 19, 2006)

Well....I guess the frame material heats up an imperceptible amount. Not all energy is returned. But I'm being pedantic. It's not about stiffness, its about how the bike feels. Thats all.


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## dcgriz (Feb 13, 2011)

Pirx said:


> I will note that it is indeed possible to make the vague concepts you are referring to precise, and test them. It is telling that nobody has ever performed such a test. .


 It seems to me that the issue is also heavily weighted towards efficiency of motion and as such can not be holistically tested within the walls of a lab because of the effect of the vary many variables involved with real life cycling and because of the unique reactions each one of us has to them. Creating a model to accurately account for all of these variables would be a Herculean task, possibly not conclusive and with doubtful economic return for the company funding it. Much easier to call a frame "laterally stiff but vertically compliant" and let people gravitate to it.

Regarding BQ, Jan Heine's claims on the flexier frames are based on tests from riding the bikes and cataloging impressions and time trials. Both can be argued against because they seem to be heavily weighted towards perception and circumstances but they seem to work for his style of riding and the equipment he uses.

Nevertheless, different bikes feel different than others and if I like the way the bike rides I really don't care about anyone's tests agreeing or disagreeing with me.


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## GlobalGuy (Jun 9, 2015)

Pirx's explanation regarding kinetic energy is illuminating.


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## Randy99CL (Mar 27, 2013)

Pirx said:


> If some of the energy input by the rider is used to temporarily flex the frame, once the frame un-flexes the energy is returned. All of it. No energy is lost. None. At. All.


You are ignoring the fact that the energy used to flex the frame is not contributing to propelling the bike forward. It's wasted, whether it is returned or not.

There is no doubt that a frame that directs 100% of the force on the pedals to the rear wheel will be more efficient than one that wastes energy in sideways movement of the BB.
Even if the loss is only a couple of %, that makes a real difference to a pro.

Edit: And this could be tested and proven, although it should be obvious to anyone who thinks about it.
A crank and BB could be attached to a block of steel with a chain to a power meter. Work the pedals with hydraulic or air cylinders that could exert measurable and consistent force.
Recreate the same setup with a flexible BB mount. Measure the difference.


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## TmB123 (Feb 8, 2013)

How much power would be lost by a rubbing chain on the FD cage because of a flexy bottom bracket. Anything at all measurable? I know it isn't power loss by the frame itself, but still an effect of it if at all significant.


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## HFroller (Aug 10, 2014)

I don't care about the issue, but I don't understand the reference to energy conservation. Energy is conserved, but so what? In thermodynamics you can have two processes that both "conserve energy" but in one case one can't extract "useful work" out of the process and in the other case one can. 

Perhaps this conserved energy is telling something interesting about frames, stiffness etc., perhaps not. Quite a few details should be specified before a conclusion is possible.


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## Pirx (Aug 9, 2009)

robt57 said:


> I can do 80 miles hard on my Addict, and 50 would bring me closer to being tired and slowing in the last 10 that on the 2005 flexy [albeit very comfortable] Roubaix.
> 
> Obviously my imagination...


No, you misunderstand. I had said, in my very first post that started this thread, that it is possible that there can be benefits of stiffness to be found in the rider-bicycle system. However, these are subjective in the sense that they can vary from rider to rider. Some riders may indeed benefit, some others won't. There are still many, many cyclists around who love the ride of the typically far more compliant steel bikes, including having no issues with "efficiency". 



robt57 said:


> Should have known better than to take the troll bait anyway..


Interesting reaction.


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## Pirx (Aug 9, 2009)

Randy99CL said:


> You are ignoring the fact that the energy used to flex the frame is not contributing to propelling the bike forward. It's wasted, whether it is returned or not.


I am not ignoring anything. The "fact" you mention does not exist. 



Randy99CL said:


> There is no doubt that a frame that directs 100% of the force on the pedals to the rear wheel will be more efficient than one that wastes energy in sideways movement of the BB.


On the contrary, the detailed kinematics of the rider-bicycle system is complex enough so that nobody understands it to the level required to assess the loss, or benefit, of a flexible frame. However, it is easy to see, in principle, how the motion of the frame when returning from a flexed state can indeed contribute to the propulsion of the bicycle. The idea that this sideways motion of the bottom bracket necessarily wastes energy is naïve, given that there is no energy dissipated in the frame itself.



Randy99CL said:


> Edit: And this could be tested and proven, although it should be obvious to anyone who thinks about it.


This only seems obvious to someone who does not understand the physics. What you find obvious is simply wrong.



Randy99CL said:


> A crank and BB could be attached to a block of steel with a chain to a power meter. Work the pedals with hydraulic or air cylinders that could exert measurable and consistent force.
> Recreate the same setup with a flexible BB mount. Measure the difference.


If you perform this experiment, and do it right, you'll find _exactly_ zero difference. Anybody with a minimal understanding of the requisite physics will understand that, which is why your "test" is pointless. But by all means, feel free to perform that test.


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## Pirx (Aug 9, 2009)

tvad said:


> The take-away of the thread.


Well, then why don't you explain how you know it's those elusive benefits of stiffness of that Cervelo of yours that is responsible for your presumably better performance, rather than the clear advantages of lower weight and better aerodynamics. Alternatively, let us know what percentage of your increased performance is caused by the three variables, respectively.


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## skepticman (Dec 25, 2005)

For a typical recreational rider plugging along and averaging 14-17 MPH, it's not just stiffness that's a fairytale, but also weight and aero. Ignorant people who keep upgrading to newer bikes which they think will make them faster are fools believing the marketing hype who are being parted with their money. It's very unfortunate that so many bike manufacturers and bike shops rely on perpetuating this myth for much of their business. The only people who should be worrying about faster bikes are racers competing for money who have trained as hard as they can and need every advantage. These people are a tiny minority of the bike buying population.

I was once one of those dummies who believed a lighter and stiffer carbon bike could make me faster. Now I know the truth: that a custom frame that is built to fit me, for my weight, and with desired ride quality will motivate me to ride more frequently and for longer distance. This is what will make you faster. The most efficient vehicle in the world will still be slower without a powerful motor.

It's very curious that grand tour average speeds haven't increased significantly over the years, despite bikes being lighter, stiffer and more aero, tires having less rolling resistance, ceramic bearings, improved training and nutrition, etc.

Then there's the fact that no one bike brand consistently dominates races. It's constantly a different brand of bike winning a stage or a race. And riders on the same team riding the same brand of bike have times varying by many minutes or hours. That is all the proof anyone needs that the rider makes a far bigger difference than the bike.


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## ibericb (Oct 28, 2014)

There are a couple of companion BQ blog posts that came late last year that help explain long-debated issue of frame flexibility, power transfered, performance, and importantly overall rider perception. They can be found here (November 2014), and here (December 2014).

As one well schooled in physics I wrestled with this in my own mind for years. In the second of those links (December 2014) the blog authors note a series of finite element analysis simulations which found that the work done to flex the frame during pedaling is returned to the drivetrain on the return (spring rebound). If the finite element analysis simulations run for BQ's work are representative and valid, then they resolve a big part of the question. Yes the frame flexes, so how much power is lost between the pedals and wheels as a result of that frame flex? The answer is very, very little. The remaining source of power lost would be the hysterical loss between material deformation and rebound. For the rigid materials typically used in bike frames, and the small elastic deflections that would be rational, that loss is probably negligible. So, from a purely physical look it appears that frame flexibility is, in fact, not a source of power losses.

The great debate over power loss and frame flexibility seems to revolve mostly around differences in perceptions between different riders. Part of that is possibly due to a difference in perceived effort between frames of different stiffness. That perception is grounded in the resistance the rider experiences when he applies force to the pedals (it's in their legs, not their head). It extends then to apparent acceleration. If the BQ test results are representative, a rider should be able to develop more power on the more flexible frame. I suspect, however, this has a limitation, and that for any given rider there is an optimum flexibility that facilitates the optimal development of sustained power output for that rider. Regardless, the impact of frame flexibility on a rider's ability to develop power complicates the issue, as it focuses on the rider's ability rather than the original question of applied power lost to work being done to flex the frame back and forth.

The BQ work makes a key point, which I believe is understated. At the end of the day it's about the total performance of bike + rider that matters most. That includes a riders ability to develop power as well as the bikes response to that input. Both of those will probably vary between different riders as well as riders with different objectives at varied times.


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## goodboyr (Apr 19, 2006)

Oy vey.........
Now the same old crap gets trotted out. This thread was started with science, and now ends with internet science.


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## wim (Feb 28, 2005)

skepticman said:


> It's very unfortunate that so many bike manufacturers and bike shops rely on perpetuating this myth for much of their business.


Perpetuating such a myth is at the very core of all businesses wishing to make a lot of money selling luxury goods. Good bicycles can easily last 20 years, so the manufacturer must find a way to separate the buyer from his bicycle long before those 20 years are up. Suggesting that his 2-year old bicycle is out-of-date and that he therefore needs a new one is about the only way to do that.


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## ibericb (Oct 28, 2014)

goodboyr said:


> Oy vey.........
> Now the same old crap gets trotted out. This thread was started with science, and now ends with internet science.


Specifically what "old crap" are you referring to, and what makes it "crap" in your mind ?


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## Jay Strongbow (May 8, 2010)

I can't recall see any marketing saying a stiffer bike makes you faster. They just tout stiffness from what I've seen.
I don't know anyone who sprints who doesn't like the feel of a stiff BB area.
I haven't read the whole thread but not sure what the hub bub is about. People like stiff bikes and companies make them. That's about it for this topic as far as I can see.


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## crit_boy (Aug 6, 2013)

TmB123 said:


> How much power would be lost by a rubbing chain on the FD cage because of a flexy bottom bracket. Anything at all measurable? I know it isn't power loss by the frame itself, but still an effect of it if at all significant.


I stopped riding my custom steel frame (built for racing crits) for this reason. It was built for me when I raced at 145 pounds. As I got older and fatter, I could see the chain rings nutating under power. I could readily cause the ring to move a couple mm - enough to rub both sides of the derailleur cage. 

I know a steel frame can be made differently and built with a more appropriate tube set for my current weight and power. However, that frame flexed enough to see and to cause the chain to rub the derailleur. The bike is my favorite bike, but I don't ride it anymore. 

Currently, I ride a venge - which is actually a bit more 'relaxed' in geometry than the steel bike. The venge is pretty stiff in the BB and has very little vertical compliance. While "science" may say there is no difference between the power efficiency of my old steel frame and my venge, a quick ride on a bumpy road or an all out sprint will tell you something different.

At the end of the day, it is about feel and personal preference. But, I am not buying that there is no discernible difference in frame flex between a Rivendell and a Tarmac. Since you can feel a difference, the difference matters.


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## crit_boy (Aug 6, 2013)

goodboyr said:


> This thread was started with science, and now ends with internet science.


The thread did not start with science*. 

The thread started with a citation to a bicycle maker selling an idea that flexible frames are the way to go. 

From a marketing standpoint, how is that different than other manufacturers selling an idea that stiff frames are the way to go?


*A "double blind" test comprising the author and two other individual's performance impressions of two frames of different relative stiffness is not quite conclusive evidence.


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## Pirx (Aug 9, 2009)

Thanks, ibericb, for your input, and those references! I appreciate your help in getting this debate back on a rational footing, which, as this thread shows, is harder than I expected. Frankly, I have a bit of trouble understanding the obvious emotional attachment of some of the posters to this silly notion of the superiority of the (laterally) stiff frame.



> At the end of the day it's about the total performance of bike + rider that matters most. That includes a riders ability to develop power as well as the bikes response to that input. Both of those will probably vary between different riders as well as riders with different objectives at varied times.


Couldn't have said it any better.


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## Pirx (Aug 9, 2009)

crit_boy said:


> The thread did not start with science*.
> 
> The thread started with a citation to a bicycle maker selling an idea that flexible frames are the way to go.


That was just meant as an illustration. The main point is indeed that science does not provide any support for the idea of the benefit of reduced frame flex, at least within a realistic range of "serious" road bikes from within the last 20 years or so.



crit_boy said:


> A "double blind" test comprising the author and two other individual's performance impressions of two frames of different relative stiffness is not quite conclusive evidence.


Absolutely, I agree, it's not conclusive at all. But, it's a lot more evidence than anyone else in this debate has ever offered.


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## Teuthis (Jul 29, 2015)

K, thought experiment: what if a rider's foot were coupled to the pedal through a coil spring?


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## goodboyr (Apr 19, 2006)

ibericb said:


> Specifically what "old crap" are you referring to, and what makes it "crap" in your mind ?


The concept of "planing" and the attempt to take make an experiment and scientific conclusion out of something where there are a large number of other independent and dependent factors that are not isolated or controlled.


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## Pirx (Aug 9, 2009)

Teuthis said:


> K, thought experiment: what if a rider's foot were coupled to the pedal through a coil spring?


Excellent analogy. Now make sure that coil spring has a maximum deformation of perhaps a tenth of an inch, and ask how things will change if you replace that spring with one that deforms only a twentieth of an inch. Perform the experiment and let us know.


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## ibericb (Oct 28, 2014)

goodboyr said:


> The concept of "planing" and the attempt to take make an experiment and scientific conclusion out of something where there are a large number of other independent and dependent factors that are not isolated or controlled.


I spent over 40 years of my life designing and doing scientific experiments in research labs. I've written and reviewed hundreds of published peer reviewed research papers, grant proposals, etc. I have yet to see even a single experiment that controls ALL of the variables in a complex system. That doesn't make the work or attendant conclusions any less valid, so long as it is recorded and reported accurately.

When you have some real measurable results to present, or can provide another source with at least comparable design and control, then please bring it. Until then your attempt to dismiss some reasonable work is nothing more than ungrounded drivel.


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## Randy99CL (Mar 27, 2013)

goodboyr said:


> The concept of "planing" and the attempt to take make an experiment and scientific conclusion out of something where there are a large number of other independent and dependent factors that are not isolated or controlled.


Look at my first response. The machine I described would work because it eliminates any human interaction.
The pressure driving the cylinders could be adjusted and measured and would be consistent. It's impossible for any human to put consistent force into anything.

I agree that human "perception" is scientifically useless. People can ignore reality and delude themselves into believing anything. Hence this thread.

The goal of a bike is to propel itself (and the rider) forward. Any energy that does not do exactly that is wasted. Only that pedal force that is transferred to driving the rear wheel is useful.
Any force used to flex the BB is at a 90 degree angle to what drives the wheel. It does not contribute to driving the bike forward; it can't, the bike can't convert energy in one direction into force in another. Doesn't matter how much of that force is eventually returned, it's in the wrong direction.

So it's simple. *Describe exactly how the side-to-side movement of the BB contributes to driving the bike forward*.


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## cxwrench (Nov 9, 2004)

Pirx said:


> That test has been done, with some 1983 steel steed (Pinarello) versus a modern carbon bike (2009 Lapierre). Result, in a nutshell: No difference.
> 
> 
> 
> The difference was all in your head, at least the difference caused by increased stiffness. Stiffness has no measurable effect on acceleration, and no effect on average speed. Your Cervelo is lighter, hence the better acceleration, and *much more aerodynamic*, thus higher average speed. Nothing to do with stiffness.


It's actually much less aerodynamic with its huge 'squoval' tubes. Stiffer, yes. More aero, no way.


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## cnardone (Jun 28, 2014)

this is all gut feeling in my head logic. Nothing that has to do with anything resembling science. With that said, there has got to be some......floor or fit for purpose here. Meaning, there must be a level of flex in which an further reduction in flex there would be no performance increase yet, increased flex would show degradation of performance.

crazy idea?


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## duriel (Oct 10, 2013)

Who won?

OK, here it is. If your frame flexes, it does limit the acceleration. This is why...
Acceleration is force acting on mass. If your frame flexes, when you hit the maximum force, the frame flexes limiting the force to some level less than that maximum. Therefore your maximum acceleration is less. 
This force is returned to the system when the frame unflexes, but at that point the output level may not be there to allow the use of the force.


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## Teuthis (Jul 29, 2015)

Pirx said:


> Excellent analogy. Now make sure that coil spring has a maximum deformation of perhaps a tenth of an inch, and ask how things will change if you replace that spring with one that deforms only a twentieth of an inch. Perform the experiment and let us know.


Considering the springyfoot suggests many questions, most of which ibericb has addressed already. Most importantly, not "Is there any flex," but "How much flex under what conditions, and does it matter anyway?"

I got to wondering about time: if the rider compresses his springyfoot, but the spring then extends before 6 o'clock crank position, is any power actually lost (not counting negligible heat in the spring) or just displaced a bit in time? The result of which would be a "feel" issue, as noted by ibericb?

And maybe a little flexy is desirable, aka, compliance? And whattabout super lightweight bikes that are so spindley that stiffness becomes a bigger issue? What if the flex stored in the frame rebounds vertically against gravity, rather than rotationally in the crank?

The springyfoot analogy got me thinking all this. And indeed, Pirx, seems some real science could be done (or shared if already done) to clarify this. But contemplating the experiment yields a pile of variables: rider weight, power, cadence, subjective feel, frame size and type, wheels, tires, inflation, blah, blah. 

I have no idea myself, of course, and I'd like a clue so my next bike purchase can be more informed than "Stiffer is better! Buy now!" But thinking about it seems to indicate that there's plenty to think about.


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## Pirx (Aug 9, 2009)

Randy99CL said:


> Look at my first response. The machine I described would work because it eliminates any human interaction.


Notice that I had already answered this one. The mechanics in your experiment is simple enough to be fully understood. The answer is, there is exactly zero difference. Take it from someone who has published many, many research papers in the general field of theoretical mechanics.



Randy99CL said:


> So it's simple. *Describe exactly how the side-to-side movement of the BB contributes to driving the bike forward*.


That's trivial, in principle: Imagine the pedal fixed in space, held in place by a foot that's not moving. Now have the BB rotate (obviously, it's not just a side-to-side motion) as it will when the frame un-flexes. Result: there will be an incremental rotation of the crank axle, which can generate a propulsive force. Of course, in reality such motions will be superimposed on the "normal" crank rotations, and relative phases matter. Here's the thing: For someone who actually understands the physics of this, these details are irrelevant. Moreover, it is understood that the exact details you are asking for are extremely complex, and that common-sense intuition is mostly useless in an attempt to assess the energy gains or losses.



duriel said:


> Acceleration is force acting on mass.


No, acceleration is acceleration, not a force acting on anything. Acceleration _results_ from a net force acting on a mass. Words have meanings, a nd meaning is important.



duriel said:


> If your frame flexes, when you hit the maximum force, the frame flexes limiting the force to some level less than that maximum.


No, frame flex has exactly nothing to do with limiting the force. The force is exactly the same.



duriel said:


> Therefore your maximum acceleration is less.


No, it isn't.



duriel said:


> This force is returned to the system when the frame unflexes, but at that point the output level may not be there to allow the use of the force.


Huh? I cannot parse this into anything meaningful.

Bottom line: Don't even try to understand the mechanics of this process based on some vague remnants of your high-school physics, if any. You either understand energy conservation, in which case you can make some general statements that are precise, or you don't, in which case you'd be forcing yourself into either experiments, or very detailed computer simulations. Both of these will typically be far beyond your reach, and grasp.


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## ibericb (Oct 28, 2014)

Randy99CL said:


> ...So it's simple. *Describe exactly how the side-to-side movement of the BB contributes to driving the bike forward*.


The determination that a frame's lateral flex does not lead to power loss is not new. The BQ work relied on a new FEA to ascertain or confirm what was explained well in 1974 by Calspan in a research report done for Schwinn. In that report you will find both the mathematical evolution and proof of the concept , as well as some limited practical test results to determine the extent of lateral and vertical deflection on different Schwinn frames of the era.

Quoting from that report:

_"For all pedal force deflection curves which go through zero at the deflection extremities, any energy which is lost in frame deformation at a particular instant is subsequently recovered fully in the form of propulsive energy, since the instantaneous spring energy, and therefore the cumulative energy lost in propulsion, returns to zero at every half cycle of the rider's force deflection curve. The only qualifications to this conclusion arise from conditions previously stated, specifically:

• that the forces between rider and bike are as shown in Figure 2c 

• that energy lost in the form of heat in the frame material is neglected."_​
An explanation of the physical mechanisms that follows the preceding proof will be found on page 13 of the report, which you can read for yourself.

There is a very important caveat to note, that is well explained in that report, and that is the elastic return of propulsive force is dependent upon the force applied to the cranks vs. crank position (the first qualification noted above). That result is predicated upon zero force application with the pedals in their 12 and 6 o'clock positions. That is the fairly normal and typical seated force profile, or very near it. A departure from the efficient return of propulsive force would be expected when the rider applies appreciable force when the pedals are near vertical. That might typically be expected in an out-of-saddle extreme pedal force situation, such as climbing or sprinting. In those situations then some small fraction of the force applied by the rider to the pedals at those positions should be expected to be lost by spring work being done directly on the rider himself in a way that cannot be converted into propulsive force. However, force being applied at those positions in likely from supportng the rider's weight, and would not be constructive in propulsion to any significant degree anyway.


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## Jwiffle (Mar 18, 2005)

Randy99CL said:


> *Describe exactly how the side-to-side movement of the BB contributes to driving the bike forward*.


I'm no expert on physics, but I think the side-to-to side movement of the BB is irrelevant to forward propulsion. The force going down on the pedals turns the crank around, driving the chain and thus the rear wheel. Whether or not the sideways force applied by the rider flexes the frame or not would not change the downward force. I don't think you can steal the sideways force and make it down force just by making the bike stiffer. The sideways force would remain the same, just not flex the frame sideways as much if the frame was made stiffer. The sideways force always remains sideways force.

Very crude analogy: (Pirx, correct me if I'm wrong and the analogy makes no sense)
If you apply a sideways force to a lightweight ball rolling down a hill, it will go sideways, but continue downhill at same rate as it was. Apply same sideways force on a much heavier ball rolling down the hill, it, too, will continue down the hill at its same rate, but won't go sideways as easily. The sideways force will not slow either ball from its downward roll.

So, I'd agree with Pirx that frame stiffness is marketing hype. Especially since they have now been stiff enough for years that mortals can't really flex them, anyway. Recently I read a paper by a wheel company (Zipp maybe? Can't recall atm) saying they have to purposefully build flex into their wheels, because too stiff a wheel causes the rim to rub the brake pads (and then customers would complain the wheel wasn't stiff enough because it was rubbing. Customers would have had it backwards!)


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## ibericb (Oct 28, 2014)

Pirx said:


> That's trivial, in principle: Imagine the pedal fixed in space, held in place by a foot that's not moving. Now have the BB rotate (obviously, it's not just a side-to-side motion) as it will when the frame un-flexes. Result: there will be an incremental rotation of the crank axle, which can generate a propulsive force. Of course, in reality such motions will be superimposed on the "normal" crank rotations, and relative phases matter. Here's the thing: For someone who actually understands the physics of this, these details are irrelevant. Moreover, it is understood that the exact details you are asking for are extremely complex, and that common-sense intuition is mostly useless in an attempt to assess the energy gains or losses.


I believe I was penning my previous contribution when this went up. FWIW, it's the same model and explanation offered by the Calspan boys 41 years ago. That's one of the beauties of physics - valid principles are enduring.


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## Pirx (Aug 9, 2009)

Jwiffle said:


> Very crude analogy: (Pirx, correct me if I'm wrong and the analogy makes no sense)
> If you apply a sideways force to a lightweight ball rolling down a hill, it will go sideways, but continue downhill at same rate as it was. Apply same sideways force on a much heavier ball rolling down the hill, it, too, will continue down the hill at its same rate, but won't go sideways as easily. The sideways force will not slow either ball from its downward roll.


That's a perfectly fine analogy.




ibericb said:


> I believe I was penning my previous contribution when this went up.


Yep, you did. Read the article, and, yes, the mechanism described there is the same as the one I put forward. It's better explained in your article, though 

Thanks!


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## dcgriz (Feb 13, 2011)

ibericb said:


> The determination that a frame's lateral flex does not lead to power loss is not new. The BQ work relied on a new FEA to ascertain or confirm what was explained well in 1974 by Calspan in a research report done for Schwinn. In that report you will find both the mathematical evolution and proof of the concept , as well as some limited practical test results to determine the extent of lateral and vertical deflection on different Schwinn frames of the era.
> 
> Quoting from that report:
> 
> ...


Another quote from the Conclusions and Recommendations chapter of the same report:

"_These initial results show that the stiffness of a frame can be directly related to its efficiency of energy utilization, but the characteristics of the rider's input forces must be better known before this efficiency can be quantified.......the study of the rider's bicycling characteristics could be done together with energy measurements of the bicycle under actual pedaling conditions......_"

and another:

"_The relationship of frame properties to energy use is only part of the question of bicycling efficiency. Also of importance is the rider's ability to utilize a certain bicycle's design characteristics and the importance of efficiency /weight ratio in various modes of bicycling._"

which brings us back to "Try it to see if you like it".

Now, this from someone with a bit of hands-on experience on the matter: 
Frame Flex | Kirk Frameworks


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## Pirx (Aug 9, 2009)

dcgriz said:


> which brings us back to "Try it to see if you like it".


I think that's a perfectly healthy way to look at it, even apart from any performance benefits or lack thereof. Don't forget that, given the very small amount by which any modern frame flexes, if some frame indeed turns out to be less efficient _for a specific rider_, then the loss of efficiency will be minute, and well within the noise of other effects. Thus the best advice is to ride the frame you like, even if it's a more flexible one, and ignore the illiterate marketing drivel.


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## Fireform (Dec 15, 2005)

Pirx said:


> That's a perfectly fine analogy.
> 
> 
> 
> ...


It's true that the frame is storing and returning energy elastically given that the frame is not deforming, but I wonder. 

The frame is storing energy during that part of the pedal stroke where the force on the crank arm is increasing, let's say from about 2 to 5 o'clock for the right side arm. It's returning that energy as the force from the leg to the crank arm is decreasing, say from 5 to 6 o'clock. I think the unloading must be much faster than the loading. Do both flexions balance in terms of torque to the drive train? Neither one is going to be balanced by force from the other pedal.


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## HFroller (Aug 10, 2014)

ibericb said:


> The determination that a frame's lateral flex does not lead to power loss is not new. (...)
> 
> Quoting from that report:
> _"For all pedal force deflection curves which go through zero at the deflection extremities, any energy which is lost in frame deformation at a particular instant is subsequently recovered fully in the form of propulsive energy, since the instantaneous spring energy, and therefore the cumulative energy lost in propulsion, returns to zero at every half cycle of the rider's force deflection curve. The only qualifications to this conclusion arise from conditions previously stated, specifically:
> ...


This is an odd discussion. I understand the conservation of energy - I have a degree in physics. The above statements are rather trivial and meaningless. If we neglect "the energy lost in the form of heat" then the "cumulative enery lost" turns to zero.

Nobody will deny _that_. If there's no energy lost - meaning there's no heat produced, I assume - then there's no energy lost. But even if there's no energy lost and the flexed frame gives back all the potential energy it gained by being flexed - it doesn't tell you anything about your speed or the loss thereoff.


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## TmB123 (Feb 8, 2013)

I sort of started this thought by mentioning chain rub earlier - but if the frame flexes enough to rub the chain on the FD cage, does that change the chain line sufficiently to introduce some inefficiency, does it put any extra load on the crank or pedal axle bearings as force is being applied in a slightly different plane, if you twist your foot on the pedal slightly does this effect the amount of downforce you can generate, can you flex the frame enough to rub the rear wheel on a brake block. I'm not sure if any of these things lead to any loss in efficiency, I guess my question or point is if frame flex itself doesn't directly cause a loss in power, can it indirectly via what I just mentioned or anything else like them?


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## Fireform (Dec 15, 2005)

To restate my question somewhat, even though the frame is deforming elastically, does it automatically follow that there is no loss of power to the drivetrain? If the storage of energy is happening when the chain is under high tension and the return of energy is happening when the chain is under lower tension, is the power delivered to the chain the same? This is an honest question. It may be uninformed, I will admit that, but I really am curious.

A simple bow deforms elastically, storing and releasing the energy imparted by the person who draws the bow. However, if you've ever fired a bow you know that it continues to vibrate energetically after the arrow is launched. That energy is part of the energy stored in the bow when it was drawn, so all of the energy stored in the bow by its being drawn is returned when it is released, but not all of that energy goes into the arrow because it is released after the arrow is no longer engaged in the bow.


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## GlobalGuy (Jun 9, 2015)

In the sport of cycling I’m a relatively fit and long time cyclists, nothing more. In terms of sophisticated knowledge of all things related to cycling I am despite my experience little more than a neophyte. I represent what Nike used to sell; I “Just do it!

The bicycle moves as a result of the force applied by the cyclist to the bike mainly through the pedal/foot interface. How much of that a specific rider conveys to the rear wheel on a specific bike is a big factor on how fast the bike moves. If the force transferred, however measured, is 95 percent that bike will move faster than if anything less than 95 percent is transferred. (All other things being equal.) What variables or conditions can cause an interference or impedance in the transfer of power along the “chain?” Many of them we know. Some we may not.

Regarding what impact if any does the stiffness of the bottom bracket seems based upon what I read debatable or unsettled even if there is a majority or consensus opinion one way or the other on that issue.

One thing for sure is that for optimal enjoyment and performance among the many factors the rider has to be happy with the setup. That includes from their subjective perspective the stiffness of the BB and its impact.


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## SwiftSolo (Jun 7, 2008)

You seem to be treating stiffness as a single property. Stiffness where? Vertically or laterally? Everybody will like compliance vertically. Nearly everybody will like stiffness laterally. How you obtain both is the question frame builders have been working on for some time.


Pirx said:


> That test has been done, with some 1983 steel steed (Pinarello) versus a modern carbon bike (2009 Lapierre). Result, in a nutshell: No difference.
> 
> 
> 
> The difference was all in your head, at least the difference caused by increased stiffness. Stiffness has no measurable effect on acceleration, and no effect on average speed. Your Cervelo is lighter, hence the better acceleration, and much more aerodynamic, thus higher average speed. Nothing to do with stiffness.


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## Z'mer (Oct 28, 2013)

ibericb said:


> There is a very important caveat to note, that is well explained in that report, and that is the elastic return of propulsive force is dependent upon the force applied to the cranks vs. *crank position* (the first qualification noted above). That result is predicated upon zero force application with the pedals in their 12 and 6 o'clock positions. That is the fairly normal and typical seated force profile, or very near it. A departure from the efficient return of propulsive force would be expected when the rider applies appreciable force when the pedals are near vertical. That might typically be expected in an out-of-saddle extreme pedal force situation, such as climbing or sprinting. In those situations then some small fraction of the force applied by the rider to the pedals at those positions should be expected to be lost by spring work being done directly on the rider himself in a way that cannot be converted into propulsive force. However, force being applied at those positions in likely from supporting the rider's weight, and would not be constructive in propulsion to any significant degree anyway.


The point about crank position has not been discussed. Conversely to what you stated, any return force from frame flex close to pedal positions 6 or 12 o'clock would also be lost. That's because the frame unwind torque that is returned to forward motion is dependent on pedal position and force when the unwind happens, as stated above. 
This assumes that the unwind force come from the pedal offset torque on the frame. 

The work returned needs to produce crank torque, and that depends on crank angular position relative to the unwind force. 

The experiment here is to stand still balancing the bike, and weight and unweight one pedal in the 6 o'clock position - the bike will obviously not move forward. But you will be flexing the frame, doing work to flex, and getting it back when you unweight.

Not saying stiffness makes a difference, or not. But different pedal strokes, or even cadence, may be a factor.


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## Migen21 (Oct 28, 2014)

Many years ago (mid-80's I guess), when I was actively racing, I was on a training ride with the team I raced for. We were riding up Ute Pass out of Colorado Springs. I was riding a fairly inexpensive 25" (63cm) Fuji steel racing bike(don't recall the specifics). At one point, during a particularly steep part, I was up out of the saddle, the coach, who had been riding behind me, pulls up to my side and started talking about frame flex. I'm 6' 5" and in those days was a pretty powerful rider As he was talking about the subject, I looked down and realized just how much the entire frame was twisting as I torqued back and forth on the handlebars. 

Later, as a demonstration of how much energy goes into actually flexing a bike frame, he put the bike in a trainer stand and had me stand on the pedals and attempt to flex the frame the same way I was flexing it as I was riding up the pass. It's really hard work to bend a bike frame. 

Consider how many pedal strokes it took me to climb up that pass. Imagine standing over the bike in your trainer and just manually flexing it the same amount that many times. 

It may be difficult, or even impossible to quantify lost energy to flexing a frame, there is no doubt that it happens. More importantly though, is that this flexing, however small it may be, is repeated hundreds or thousands of times per ride.


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## aclinjury (Sep 12, 2011)

ibericb said:


> There are a couple of companion BQ blog posts that came late last year that help explain long-debated issue of frame flexibility, power transfered, performance, and importantly overall rider perception. They can be found here (November 2014), and here (December 2014).
> 
> As one well schooled in physics I wrestled with this in my own mind for years. In the second of those links (December 2014) the blog authors note a series of finite element analysis simulations which found that the work done to flex the frame during pedaling is returned to the drivetrain on the return (spring rebound). If the finite element analysis simulations run for BQ's work are representative and valid, then they resolve a big part of the question. Yes the frame flexes, so how much power is lost between the pedals and wheels as a result of that frame flex? The answer is very, very little. The remaining source of power lost would be the hysterical loss between material deformation and rebound. For the rigid materials typically used in bike frames, and the small elastic deflections that would be rational, that loss is probably negligible. So, from a purely physical look it appears that frame flexibility is, in fact, not a source of power losses.
> 
> ...



thanks for the links for the 2 articles. very enlightening and interesting read regarding frame flex.

One question I'm wondering about "planing". Since it is such a tuned process requiring the flexibility of the frame to match the power output of the rider, then it would be difficult for a person to go buy a frame that is optimized for him, right. Because the buyer and builder would need to spend time testing out different frames together, in an environment where there is a means to measure power output.


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## ibericb (Oct 28, 2014)

Z'mer said:


> The point about crank position has not been discussed.


Um, I thought that's what I did - discuss the importance of pedal position for recovering the energy stored in the frame as propulsive power.



> Conversely to what you stated, any return force from frame flex close to pedal positions 6 or 12 o'clock would also be lost. That's because the frame unwind torque that is returned to forward motion is dependent on pedal position and force when the unwind happens, as stated above.
> This assumes that the unwind force come from the pedal offset torque on the frame.
> 
> The work returned needs to produce crank torque, and that depends on crank angular position relative to the unwind force.
> ...


Not conversely at all, it is what I stated, or at least tried to. Did you actually really read the comment you quoted ? Your thought experiment description is, however, a nice way of illustrating the point, so I do appreciate that.





Migen21 said:


> Many years ago (mid-80's I guess), when I was actively racing, I was on a training ride with the team I raced for. We were riding up Ute Pass out of Colorado Springs. I was riding a fairly inexpensive 25" (63cm) Fuji steel racing bike(don't recall the specifics). At one point, during a particularly steep part, I was up out of the saddle, the coach, who had been riding behind me, pulls up to my side and started talking about frame flex. I'm 6' 5" and in those days was a pretty powerful rider As he was talking about the subject, I looked down and realized just how much the entire frame was twisting as I torqued back and forth on the handlebars. ...


While I have no doubt you moved the frame by a significant amount, that movement and the attendant force required doesn't necessarily equate to a loss of propulsive force being transfered to power at the rear wheel, but it could, and that's the point.

Consider the weighting the pedal in the 6 o'clock position with the right foot, bike leaned well to the left for balance, the bottom bracket is flexed well to the left. Now ask yourself did you lose power to turn the crank in doing that? How much of the force being supplied by your weight at the 6 o'clock position is used to turn the crank? I suspect not much at all. If it were in fact zero you haven't lost any power in moving the frame back and forth, rather the frame is supporting your weight, as it does anyway in a pure vertical load, but now that load is a combination of vertical and lateral loads.

The point is the frame flexing laterally is no more a sign of power lost than the frame flexing vertically.

If, however, when lateral frame flex is a result of force being applied to the pedals to turn the crank, which can come from your weight as when you first stand on the pedals as they move between 12 and 3 o'clock (as viewed form the right side), then power could be lost if, when the frame returns as that phase of the power cycle moves past peak, the foot and pedal are not in a position to translate that return spring movement into crank rotation (e.g., 6 o'clock). This is where the interaction of the rider and bike comes into play, and rider technique becomes a key factor in determining efficiency in force to power conversion.



> It may be difficult, or even impossible to quantify lost energy to flexing a frame, there is no doubt that it happens. More importantly though, is that this flexing, however small it may be, is repeated hundreds or thousands of times per ride.


It's not difficult to determine how much work it takes to move the frame a fixed amount. But moving the frame doesn't necessarily equate to power lost in propelling the bike forward. When you sit on the bike in a pure vertical orientation the frame flexes vertically. When you lean the bike one way or the other the frame also flexes laterally. In neither case does that flex from a weight load (a force) indicate a loss of propulsive power.


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## ibericb (Oct 28, 2014)

aclinjury said:


> ...
> One question I'm wondering about "planing". Since it is such a tuned process requiring the flexibility of the frame to match the power output of the rider, then it would be difficult for a person to go buy a frame that is optimized for him, right. Because the buyer and builder would need to spend time testing out different frames together, in an environment where there is a means to measure power output.


If you could pin down for what regime you would want to optimize a frame for force-to-power conversion alone, then I guess it could be done, but it would probably be a series of experiments. The broader problem is what regime to optimize for - steady state seated on the flats, climbing, standing sprints, ... ? As I understand it the key variable is the power development cycle vs. pedal position, and attendant foot/pedal position when the frame rebounds. So pick the pedal force cycle you want to optimize for. Appreciate that you would probably be compromising other performance elements if you heavily weight on just the force-to-power conversion aspect.

The more practical approach is to choose a bike by trials across a representative range for your intended use, and figure out what works best for you reasonably broadly in that riding situation. That could lead to different preferences or bikes for nominal road conditions vs. heavy climbing vs. crtis vs. ...


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## goodboyr (Apr 19, 2006)

ibericb said:


> I spent over 40 years of my life designing and doing scientific experiments in research labs. I've written and reviewed hundreds of published peer reviewed research papers, grant proposals, etc. I have yet to see even a single experiment that controls ALL of the variables in a complex system. That doesn't make the work or attendant conclusions any less valid, so long as it is recorded and reported accurately.
> 
> When you have some real measurable results to present, or can provide another source with at least comparable design and control, then please bring it. Until then your attempt to dismiss some reasonable work is nothing more than ungrounded drivel.


Well, there you go. I say "crap".... You say " drivel". I guess we are even...enjoy your mental masturbation exercise. My only point was that as pirx says, there doesn't seem to be any science supporting the contention........except of course the "science" you have presented on "planing". Cervelo instrumented bikes and tried to determine what characteristics and direction of stiffness resulted in better " feel". That's about as "scientific" as it gets. But of course, via your appeal to your authority, only your opinions are correct.


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## ibericb (Oct 28, 2014)

goodboyr said:


> Well, there you go. I say "crap".... You say " drivel". I guess we are even...enjoy your mental masturbation exercise. My only point was that as pirx says, there doesn't seem to be any science supporting the contention........except of course the "science" you have presented on "planing". Cervelo instrumented bikes and tried to determine what characteristics and direction of stiffness resulted in better " feel". That's about as "scientific" as it gets. But of course, via your appeal to your authority, only your opinions are correct.


All of that, and still you bring absolutely nothing, except more drivel. 

Maybe you should actually read through the thread, and note the link to research done 41 years ago by Calspan. Have a nice day.


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## goodboyr (Apr 19, 2006)

You missed my point. I am agreeing with the OP on this. But the specific point I am making is that the experiment you presented with the link to the "planing" discussion should not be used as absolute proof you are correct and all others are wrong. I know you like to post links to papers that support your position.....good for you. But this is a discussion forum, and there are many points of view. I'm sure that there are a bunch of people out there who have opinions on this, want to join in the discussion, but turn away when you come on board, and declare all others to be wrong. Ride safe, the weather is still nice out there in the real world away from this forum.


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## ibericb (Oct 28, 2014)

Don't recall that I declared anyone wrong. I just asked for you to bring something of merit. That seems to elude you.

BTW - if you actually read all the posts previously made, including the sources provided by both the OP and me, you would appreciate that the "experiment I presented" as you like to refer to it (I didn't present it, Jan Heine did) is the exact same experiment that was cited in the blog entry the OP pointed to. The blog entries I provided were merely updates by the same authors, referencing the same research they did in 2008, as well as the previous blog entry the OP pointed to. So if you agree with the OP's points, it escapes me why, pointing to the same sources and experimental findings, that you take issue with citations to which I pointed and summarized (which the OP agreed with). They are the same. One further point, the analogy to "planing" was Jan Heine's, not mine. As best I recall prior to this post I never mentioned it, not once.


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## Z'mer (Oct 28, 2013)

ibericb said:


> Um, I thought that's what I did - discuss the importance of pedal position for recovering the energy stored in the frame as propulsive power.


Sorry, meant to imply, but should have said, "was not discussed _in this thread_ _until your post_", which I quoted.


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## ibericb (Oct 28, 2014)

Z'mer said:


> Sorry, meant to imply, but should have said, "was not discussed _in this thread_ _until your post_", which I quoted.


Cool. So I take it we agree on the physics, and thier impact on power.


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## Z'mer (Oct 28, 2013)

ibericb said:


> If, however, when lateral frame flex is a result of force being applied to the pedals to turn the crank, which can come from your weight as when you first stand on the pedals as they move between 12 and 3 o'clock (as viewed form the right side), then power could be lost if, when the frame returns as that phase of the power cycle moves past peak, the foot and pedal are not in a position to translate that return spring movement into crank rotation (e.g., 6 o'clock). This is where the interaction of the rider and bike comes into play, and rider technique becomes a key factor in determining efficiency in force to power conversion.


This is the point I was trying to move the discussion to. You really need to start the analysis not with the frame, but with the torque at the crank. 

I think if you agree one can flex the frame at 6 and 12 o'clock, you'll agree that you can flex it at all other angles in between. But the torque generated by the rider cannot (easily) be made at all angles.

To simplify, for vertical right pedal force only, maximum rear wheel drive torque occurs at the 3 o'clock position. Again vertical force only, zero torque is produced at 6 and 12. In between the torque follows a curve going from min to max depending on crank angle. 

So let's say some peak down force on pedals, at a certain crank angle, is lost to producing rear wheel drive torque (by flexing the frame). You will recover the lost torque when the frame unflexes _only if the unflex occurs at a complimentary crank angle from the vertical axis_. 
Example - peak right pedal frame flex occurs at 2 o'clock, unflex occurs at 4 o'clock. These positions have the same angle delta angle from vertical, so you recover the lost torque. 

But if peak frame flex occurs at 3 o'clock, and unflex at 5 o'clock, the delta angles from vertical are not equal, and you will lose torque to frame flex that could have gone to the rear wheel instead.

Of course, the opposite could also happen. If you have a flexible frame, and get max frame flex at say 1 o'clock, and unflex at 4 o'clock, you will have converted the unwind flex into more drive torque than _you could have made at 1 o'clock_.

With new power meters based on crank arm strain gauges, these forces versus crank angle should be easily available to see what's really going on in real world situations. Or as a minimum show differences in pedal force vs. angle between riders, or same rider under a wide range of conditions.


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## Jay Strongbow (May 8, 2010)

Pirx said:


> Thus the best advice is to ride the frame you like, even if it's a more flexible one, and ignore the illiterate marketing drivel.


yeah, I've since gotten used to having a really stiff (in the bb area) frame and like it but when I first got it I wasn't too crazy about what felt like a complete lack of flex when sprinting. I felt the lack of flex prevented my pedal stroke, when sprinting only, from following it's natural path. With a bit of flex I felt more natural and like my legs followed the path they wanted to instead of being forced into a path by the frame.


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## dcgriz (Feb 13, 2011)

Jay Strongbow said:


> yeah, I've since gotten used to having a really stiff (in the bb area) frame and like it but when I first got it I wasn't too crazy about what felt like a complete lack of flex when sprinting. I felt the lack of flex prevented my pedal stroke, when sprinting only, from following it's natural path. With a bit of flex I felt more natural and like my legs followed the path they wanted to instead of being forced into a path by the frame.


Precisely. The optimum frame stiffness, or flex should I say, it is vastly dependent on what you do on the bike and on how you do it. The "planing" Jan Heine refers to as the outcome from his optimized lightweight steel tubing frame is also tailored and greatly dependent on his very smooth pedal stroke, his cruising cadence of 110 rpm and his climbing cadence of 95-100 rpm. That's racing territory performance and not representative of the typical rec rider output.

Jan Heine is the first to admit in his blog discussions that a stiffer frame under him would have required him to pedal at a slower cadence in order to "guide" the frame oscillations into "planing" territory. 

This raises the question of what happens when a rider capable of sustaining a cruising cadence of only 75-85 rpm pedals Jan's lightweight steel bike? Would he be better off with a stiffer frame? Lets also make things closer to reality and say that the uniformity of his pedal stroke is not as smooth as Jan's. 

All in all, I dont think anyone likes to ride either on 2x4's or on wet noodles. Most of us tend to prefer someplace in between. The questions of effectiveness and optimum efficiency at that sweet spot could only be partially answered quantitatively. This is where the art of building a custom frame enters the science and lets the Master builders separate from the rest.


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## robt57 (Jul 23, 2011)

dcgriz said:


> Precisely. The optimum frame stiffness, or flex should I say, it is vastly dependent on what you do on the bike and on how you do it...


And frame size, your size, your power, intended use as said. Outside of you imagination of course.


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## ibericb (Oct 28, 2014)

Z'mer said:


> This is the point I was trying to move the discussion to. You really need to start the analysis not with the frame, but with the torque at the crank. ..


That's one way of approaching it. But it gets even more complicated.

The biodynamics folks who study pedaling efficiency now typically use instrumented pedals that let them sort the total applied force into three directional components, only one of which is effective in rotating the crank. The other two occur laterally, one parallel to the crank arm axis, and the other normal to that same axis. The question you've focused on is how much of the effective force is translated into rotating the crank arm vs. how much goes into moving the frame laterally, and how much of that frame displacement can be recovered for propulsion based on crank and pedal position during relaxation. Where it gets even a bit more complicated is the related question, does lateral frame displacement (flexing) during the application of total force to a pedal change or alter the fraction of effective force as a share of total applied force? 

What all of this illustrates is really one of the made by the OP from the outset, and restated repeatedly through the thread, and that is when you introduce a real rider it gets complicated quickly. At the end of the day what works best for one rider may well differ from what works for another. What's leads to best performance depends on what is meant by performance, and on a host of attendant variables. Along with that the notion that a laterally stiffer frame is better for performance simply because stiffer means better translation of pedal applied force into power is not a valid general conclusion. It may work for some, but as a general principle it is misguided.


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## goodboyr (Apr 19, 2006)

ibericb said:


> Don't recall that I declared anyone wrong. I just asked for you to bring something of merit. That seems to elude you.
> 
> BTW - if you actually read all the posts previously made, including the sources provided by both the OP and me, you would appreciate that the "experiment I presented" as you like to refer to it (I didn't present it, Jan Heine did) is the exact same experiment that was cited in the blog entry the OP pointed to. The blog entries I provided were merely updates by the same authors, referencing the same research they did in 2008, as well as the previous blog entry the OP pointed to. So if you agree with the OP's points, it escapes me why, pointing to the same sources and experimental findings, that you take issue with citations to which I pointed and summarized (which the OP agreed with). They are the same. One further point, the analogy to "planing" was Jan Heine's, not mine. As best I recall prior to this post I never mentioned it, not once.


I've looked back through this thread and I agree that you haven't declared anybody wrong, so for that I apologize. I still think the Jan Heine stuff is a bit bogus, in particular the planing theory. But i agree in general with the overall point of this thread. Must have woken up on the wrong side yesterday.


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## ibericb (Oct 28, 2014)

Cool! 

FWIW, I don't like the planing analogy either. It's Heine's, and he uses it in his writings including a review of a Specialized Diverge in the new issue.


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## dracula (Mar 9, 2010)

Pirx said:


> This is somewhat of an old topic, and I think by now many of us understand that the still ongoing obsession with frame stiffness, in the form of "lateral stiffness", "stiff bottom brackets", etc., etc., is nothing but marketing BS. Yet, just about _every single article_ you see that presents a "review" of some new bicycle, and certainly _every single manufacturer blurb_ about the newest bike from manufacturer X still continues perpetuating this idiocy.
> 
> On the other hand, from the physics of bicycles it is entirely clear that frame flex, at the kind of level any halfway realistic, existing road bike will show, has almost exactly zero effect on the efficiency of "power transfer" (whatever that may mean; we note in passing that nobody ever bothers to define this term, and there is certainly not a single test or experiment of any kind that would demonstrate the relevance of this quantity). I have therefore argued for a long time that, if there is any effect of frame stiffness on performance at all, it would have to be sought in the biomechanical efficiency of the rider-bicycle system. However, a priori there is no reason to assume that this system will perform either better or worse using a stiffer frame. As a consequence, it may well be that some riders do better on more flexible frames, and some others may prefer stiffer ones. Bottom line: Nobody knows, and all the rest is nothing but clueless babble.
> 
> ...



I haven't read a MTB magazine for over a decade; maybe things have changed in the meantime. 

However, German 'Bike' magazine (the sister magazine of the renowed German 'Tour' magazine) did some tests in a controlled environment. This was at a time, in the 90's, when discussions were rampant of the virtues of a front suspension on a MTB vs a hardtail without suspension at all.

Their conclusion: you will lose some energy which goes into the front suspension - rocking up and down - while riding, but you will gain back the loss going over say rough surface and your body will not become as beaten up or faitigued. So it may well be zero sum game.

Hasn't Mavic done some blind tests with riders and a) they couldn't tell the difference between vertically less stiff wheels b) the stiffest wheel going uphill did not improve the rider's time when benchmarked against the least stiff wheel.


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## duriel (Oct 10, 2013)

Assuming your peak output is at 300 oclock, the pedal system is at maximum efficiency at delivering all the energy to applying torque to the cranks.
If the frame flexes a significant amount, it will return the energy at a different location in the revolution, when the torque of the rider is reduced to near equal to the torque of the return energy.
But the vector result of the returning torque @ 4 or 5 oclock will mean that the output to the rear wheel has been reduced due to the inefficiency of the pedal force at the 4 or 5 oclock location.


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## ddave12000 (Aug 16, 2013)

Having just read through this entire thread and trying to make sense of all the talk of physics and what not by people much smarter than me...

...it seems to me the main takeaway from this thread is that the only thing that really matters is personal preference. In other words, if I prefer the feel of a stiff BB it MAY result in me being faster simply because my brain is able to convert a preferred condition into greater physical output. Have I got that right?


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## ibericb (Oct 28, 2014)

ddave12000 said:


> ...it seems to me the main takeaway from this thread is that the only thing that really matters is personal preference. In other words, if I prefer the feel of a stiff BB it MAY result in me being faster simply because my brain is able to convert a preferred condition into greater physical output. Have I got that right?


Kind of, but it's more than a head game. The basic message is pick what actually works best for you, however you measure or determine it, disregarding manufacturer's promotional claims that theirs is better because ... 

When the desire is better performance, what works best must consider the combination of rider and bike, the riding situation and scenario, and what is meant by performance. What is better can easily be quite different for different riders in the same situation, and can also easily be different for the same rider in different situations.


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## tvad (Aug 31, 2003)

So...if I understand correctly...when a group of cyclists cannot agree if a stiffer frame results in quantifiable performance benefits, then the advice comes down to "buy what you like".

Isn't "buy what you like" the best advice anyway?

What exactly was the purpose of this thread? Never mind. Don't answer that.


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## goodboyr (Apr 19, 2006)

And of course wheels and tire pressure have a huge contribution on how a bike feels. .


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## ibericb (Oct 28, 2014)

goodboyr said:


> And of course wheels and tire pressure have a huge contribution on how a bike feels. .


Absolutely! For that very reason the folks at BQ like to swap the tires that come in with a bike for their evaluation to a set of Compass tires they use across different bikes of the same type/style to take tires out of the equation in their subjective evaluations. Of course that also gives them some additional opportunity to further promote their brand.


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## hppy4u (Sep 15, 2002)

Not trying to go into the physics of the the whole thread since it looks like you won't be able change too many perspectives without someone willing to take the financial plunge to do the testing. 

There is one obvious thing that people have alluded to… bikes these days seem to come with with wider tires, wider rims, and thicker chain stays/seatstays which irrefutably results in very little clearance. So with that in mind, I believe it's entirely possible for some people to experience genuine performance results. 

Since we are all sharing anecdotal stories, I know when I had 23mm wide tires on my Ridley Noah (notorious for extremely tight clearances) I have definitive proof that tire rub results in speed loss and extra power being needed to maintain or accelerate during sprints/hills. In my case, narrower tires were the only solution so this is where the wider is faster theory doesn't apply in my case ;-). 

Until manufacturers are willing to make changes in the chain stay/seatstay clearances, stiff frames will minimize some of the frame tire rub and improve one's performance.


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## Mandeville (Oct 18, 2014)

tvad said:


> So...if I understand correctly...when a group of cyclists cannot agree if a stiffer frame results in quantifiable performance benefits, then the advice comes down to "buy what you like".
> 
> Isn't "buy what you like" the best advice anyway?
> 
> What exactly was the purpose of this thread? Never mind. Don't answer that.


Very well put. Certainly true in most cases. Also what an individual wants can morph and change considerably over time as factor affecting their riding skills and goals change.


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## Pirx (Aug 9, 2009)

tvad said:


> What exactly was the purpose of this thread? Never mind. Don't answer that.


The answer to that question is in my very first post. If you care to read it. Come on, it's not that hard.


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## tvad (Aug 31, 2003)

Pirx said:


> The answer to that question is in my very first post. If you care to read it. Come on, it's not that hard.


You missed, "Never mind, Don't answer that".

C'mon, it's not that hard.


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## Pirx (Aug 9, 2009)

tvad said:


> You missed, "Never mind, Don't answer that".
> 
> C'mon, it's not that hard.


Oh. So sorry. 

Am I allowed to answer this one? You know, just in case I wanted to.


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## tvad (Aug 31, 2003)

Pirx said:


> Oh. So sorry.
> 
> Am I allowed to answer this one? You know, just in case I wanted to.


As you wrote in #83, you answered already in #1; so there's no point, unless you want to hone your typing skills.


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## robt57 (Jul 23, 2011)

tvad said:


> As you wrote in #83, you answered already in #1; so there's no point, unless you want to hone your typing skills.



Instead of riding like I have been doing while this all has been venting like a resting volcano just being only a little cantankerous. 

I only saw it again due to it coming back to the top on my initial Active Post page when I link to this crazy place. ;O

Oh, I have been riding both my stiff bikes and my less stiff bikes. Which of course is like me dreaming being the stiffness is in my imagination and all...

I am taking a stiff one to crater lake, I imagine. [the stiff part, I am going to crater lake]

Y'all have fun posting now, ya hear...


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## tvad (Aug 31, 2003)

robt57 said:


> Instead of riding like I have been doing while this all has been venting like a resting volcano just being only a little cantankerous.


Does that come in an English version?


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## looigi (Nov 24, 2010)

Go work out on a Bowflex. You can get a great workout, tire yourself out, and do no useful work. Lifting weights is the same. All the energy expended winds up as heat and waste products in your body. You've done no work outside of that. This suggests to me that flex can cause you to expend energy that does not get translated to useful work, i.e. making a bike go.


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## jnbrown (Dec 9, 2009)

Almost any bike made today is stiff enough to not effect performance.
So that should not be a consideration when buying bike, period.


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## stevesbike (Jun 3, 2002)

Pirx said:


> This is somewhat of an old topic, ....


For starting a debate supposedly about the physics of bicycle efficiency, the evidence you provide is bizarre. Subjective preferences of the sort you quote have little to do with the underlying physics issue. Weber–Fechner laws and related results from psychophysics make it clear that people cannot distinguish small physical differences of the sort you mention, so whatever underlies their preferences has nothing to do with efficiency. Supposing that people prefer flexible bikes because of underlying efficiency is nonsense - people can't even tell if their car tires are under-inflated despite the fact that underinflation results in a statistically significant decrease in efficiency. 

Regarding the underlying physical question, what studies have attempted to measure energy loss due to forces on the contralateral leg? Is the rider modeled in the FEA work someone mentioned? What is the potential energy loss due to friction between the tire and road surface when the wheel is take out of plane due to fliex? Finally, why do track cyclists prefer massively stiff frames - there's a subjective preference that conflicts with those you mention and likely reveals that road preference is based on factors other than efficiency. Track cyclists are likely a much better source of preferences, since energy loss is likely dependent at least weakly to energy input, so they are much more likely able to perceive its effects.


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## nhluhr (Sep 9, 2010)

robt57 said:


> Except some is returned back into the leg muscles instead of having been already put to the wheel.
> 
> I can do 80 miles hard on my Addict, and 50 would bring me closer to being tired and slowing in the last 10 that on the 2005 flexy [albeit very comfortable] Roubaix.
> 
> ...


dont sweat it. The guy makes it clear in many ways that he hasn't had a physics class since high school.


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## robt57 (Jul 23, 2011)

tvad said:


> Does that come in an English version?



Sans a few punctuation marks and me being the king of the run on sentence, what was really wrong.


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## Pirx (Aug 9, 2009)

stevesbike said:


> For starting a debate supposedly about the physics of bicycle efficiency, the evidence you provide is bizarre.


There's a problem of reading comprehension here. I am not providing any evidence in the strict sense of the word. I am providing an example, but that example is not real evidence for anything, for a multitude of reasons. It's just an illustration, nothing more.

My main point, if you care to read closely what I wrote rather than arguing against strawmen, is that _there is not a shred of evidence_ that would demonstrate the superiority of the stiffer frame in any respect. And, yes, that means there is no hard evidence against such an effect either. However, the onus of the proof is on he who makes the positive assertion. If someone claims that "stiffer frames are better" (in whatever way) then it is fair to ask for evidence for that assertion. If no such evidence is brought forward, then one might be tempted to dismiss the assertion as spurious. 

Just to make the situation abundantly clear for those not trained in logic: What we are saying is that the status of the assertion "stiffer frames are [better]" is exactly the same as the one of a statement like "red bikes are faster". Based on the laws of physics there is a priori no reason to assume that such a statement should be true, and no evidence exists to demonstrate its validity.

Hope that helps. Incidentally, the above also answers the rest of your questions. Feel free to ask if anything remains unclear.



nhluhr said:


> The guy makes it clear in many ways that he hasn't had a physics class since high school.


Now that one _is_ hilarious. Feel free to explain how you came to this fascinating conclusion. I'm truly on the edge of my seat here.


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## ibericb (Oct 28, 2014)

Years ago Keith Bontrager was well known for his rants about various technical topics in cycling, often maligning the press, marketing, and the like. He would periodically post those in blog format on the old Bontrager site. One of those was a five part series on stiffness, and the merits of stiffness as an attribute for cycling performance. Some of those rants were saved by others. His discourse on stiffness, all five parts in sequence, can be seen here. If you want to cut to the chase, scroll down to "STIFFNESS 5 Stiffness in 3D" near the bottom, and follow his description of a sprinter, and his view of the kind of analysis it takes to appreciate how optimal stiffness can depend upon the rider, where he concludes:

"_If the short term power at the rear wheel was plotted as a function of stiffness, the optimum may not be found to be at infinite frame stiffness. If the material damping losses are small (any bets?), then a certain amount of flexibility may actually contribute to efficiency in this case. _"​
I believe Bontrager's description of the sprinter is illustrative of how frame stiffness and rider can interact in complex ways, often unknown to the cyclist. That leads to the conclusion that more stiffness does not always translate into increased performance. A key point that this entire thread began with is to determine what works best for you, and then use that rather than fall victim to the promoted notion that stiffer is necessarily better for more power.

BTW - if you're interested in more of Bontrager's rants, some can be found here. They can be quite entertaining, as well as informative.


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## Pirx (Aug 9, 2009)

looigi said:


> Go work out on a Bowflex.


That's a terrible, terrible analogy. Quasi-static muscle "work" is a different ballgame altogether. I'm no expert in physiology at all, but it is clear that your muscles can tire when exerting a force against a static load, meaning the work done is exactly zero. However, it turns out that muscles getting tired and energy being consumed are two different animals also. The fact that flex in an entirely, wildly different system can indeed lead to wasted energy does not allow you to draw any conclusions whatsoever on its effect for the bicycle we are talking about. See the efficiency of, say, the kangaroo (very instructive example, by the way, see here), or the effect of carbon-fiber based lower leg replacements for runners. To put it quite simply, intuition is a worse than useless guide in the case of complex dynamical systems of the kind we are discussing here. In the case of the kangaroo you might argue that a cyclist on a bicycle is not a kangaroo, and you'd certainly be right, but neither is he a bowflex.


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## stevesbike (Jun 3, 2002)

Pirx said:


> There's a problem of reading comprehension here. I am not providing any evidence in the strict sense of the word. I am providing an example, but that example is not real evidence for anything, for a multitude of reasons. It's just an illustration, nothing more.
> 
> My main point, if you care to read closely what I wrote rather than arguing against strawmen, is that _there is not a shred of evidence_ that would demonstrate the superiority of the stiffer frame in any respect. And, yes, that means there is no hard evidence against such an effect either. However, the onus of the proof is on he who makes the positive assertion. If someone claims that "stiffer frames are better" (in whatever way) then it is fair to ask for evidence for that assertion. If no such evidence is brought forward, then one might be tempted to dismiss the assertion as spurious.
> 
> ...


nice try with the sophomoric sophistry, but your original post claimed that we should abandon the myth of frame stiffness - not that it was unknown whether there was any effect. If there's no evidence in favor or against it, then there's no basis for your claim that it's a myth. 

In terms of burden of proof, it's pretty straightforward to know where energy goes with a frame that doesn't deflect under load. For one that does - perhaps substantially - there are lots of plausible sources of energy loss. For the record, Cervelo did these sorts of tests with their strain gauge test bike and reported losses up to 4%. The stiff frame represents the limiting case, so the burden of proof is on those who argue that flexible frames are just as efficient or more efficient, as you seem to suggest (though that violates conservation laws).

You also clearly don't understand logic. What you stated is a proposition. Logic is the study of entailment, or the relationships among propositions. Unless you were aiming to point out that your proposition involves the law of excluded middle. The proposition "stiffer frames are [better]" has no logical relationship to "red bikes are faster." The issue of evidentiary support for an empirical, contingent proposition isn't one of logic. It's one of confirmation. I'd be happy to clarify this, as I teach undergraduate and graduate courses in mathematical logic.


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## Pirx (Aug 9, 2009)

stevesbike said:


> nice try with the sophomoric sophistry, but your original post claimed that we should abandon the myth of frame stiffness - not that it was unknown whether there was any effect. If there's no evidence in favor or against it, then there's no basis for your claim that it's a myth.


Oh please. I said that the myth (the claim that stiffer frames are universally advantageous, regardless of rider and riding scenario) should be abandoned because it is a myth. If there's no evidence for or against it, that's what it is.



stevesbike said:


> In terms of burden of proof, it's pretty straightforward to know where energy goes with a frame that doesn't deflect under load.


You really think so, huh? In the realistic, nonlinear and nonholonomic rider-bicycle system? Including the kinematics and dynamics of all the relevant joints and moving masses in the riders body? Including the nontrivial motion of the bicycle frame and the wheels? You'd make quite a splash in the literature if you were in fact able back up this fantastic claim. Why don't you lay it out for us here? After all, it's "pretty straightforward", right?

As an aside, I continue to be amazed at the misplaced confidence of some of the posters here in their understanding of mechanical systems, based on some vague remnants of half-understood high-school "physics". I'll make this brief: You quite simply do not have the slightest idea what you are talking about here. My friend tvad will now probably come along and whine about how I appear arrogant, and pretend to know more than anyone else. Well, it turns out that Theoretical Mechanics is not a simple branch of physics, at all. I happen to have worked in this and related fields for decades, so I do indeed know a lot more bout this topic than probably just about anyone else in this forum. This has nothing to do with arrogance, it's just a fact. If there's anyone else in this forum or elsewhere who has training in the field, ask them to assess what I wrote. Then we'll go from there. Deal?



stevesbike said:


> For one that does - perhaps substantially - there are lots of plausible sources of energy loss.


Name them. Forget about material damping; although present that's far too little to be of any interest to anyone.



stevesbike said:


> For the record, Cervelo did these sorts of tests with their strain gauge test bike and reported losses up to 4%.


You have a reference for this claim? 4% of what? Most importantly, please let us know how you, or Cervelo, would deduce energy losses from strain gauge measurements. Let's cut right to the chase: That's of course impossible. Perhaps Cervelo did more than you said, but then I'd be interested in what that was. I'll be honest, my guess is you don't know.



stevesbike said:


> The stiff frame represents the limiting case, so the burden of proof is on those who argue that flexible frames are just as efficient or more efficient, as you seem to suggest


Heh, nice try. Try again.

By the way, you still do not seem to understand what I am saying. Here it is again: I claim that flexible frames may be, for certain riders, or under certain load scenarios, just as efficient, or even more efficient, than stiffer frames. It's quite possible that they are less efficient in others, or for other riders. Feel free to ask if this is still unclear.



stevesbike said:


> though that violates conservation laws


Ahh, now you got my attention: Please elaborate what, and how conservation laws would be violated, if material damping is assumed negligible (which it is*). Fair warning: Your claim is complete nonsense, and unsupportable, but feel free to make a fool of yourself by trying to do the impossible.

*There's a little caveat here, but that doesn't really help your case: Material damping can be quite high in certain fiber composites. This, by the way, is the reason for some of the comfort properties ascribed to carbon fiber handlebars for example. Specifically, the related material constant is typically far higher for carbon fiber materials than for steel, say. Thus that flexible steel frame may have less internal energy dissipation than a much stiffer carbon frame.

P.S.: Oh, and before I forget, there's the question of the psychopathology of these whole discussions: I really wonder, why are people so emotionally attached to this particular fairytale? I mean, this is a simple technical question, so there should be no reason to get all religious about it. I understand the role of the idea in marketing, but why would a cyclist get all up in arms if somebody questions the stiffness myth? What's the reason for that?


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## tvad (Aug 31, 2003)

Pirx said:


> My friend tvad will now probably come along and whine about how I appear arrogant, and pretend to know more than anyone else. Well, it turns out that Theoretical Mechanics is not a simple branch of physics, at all. I happen to have worked in this and related fields for decades, so I do indeed know a lot more bout this topic than probably just about anyone else in this forum.


Hi.

First, I am not your friend; even in a jokingly sarcastic manner. Let's make that clear.

Second, you do not _appear_ arrogant. You are Webster's definition of arrogant.

I have _never_ disputed your knowledge or learning. It's sad that you cannot use your knowledge to bring people together into your discussions, but rather choose vinegar over honey.

You simply lack any tact or social skills in your posts.

In the end, if posting on RBR and displaying an aggrandizing sense of superiority is what it takes to make your day complete, then have at it.


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## Fireform (Dec 15, 2005)

If we can agree that the force being applied by the rider can be resolved into forces directed to the drivetrain, in the plane of pedal rotation, and forces directed laterally that cause the frame to load and unload, I would argue that the latter forces largely represent wasted energy in the form of isometric exercise. Whether or not the magnitude of that loss is "significant", I can't say and won't speculate. I understand that those lateral forces may also make the whole frame move side to side rather than flex. But I do think it's a real question, not nonsense.


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## goodboyr (Apr 19, 2006)

Cervelo instrumented a bike to try to correlate stiffness and vibration measurements with rider feel. Separately, before he was with cervelo, Damon rinard attempted to estimate energy losses due to stiffness. That's all.


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## Pirx (Aug 9, 2009)

tvad said:


> First, I am not your friend; even in a jokingly sarcastic manner. Let's make that clear.


Semantics, my friend, semantics.



tvad said:


> Second, you do not _appear_ arrogant. You are Webster's definition of arrogant.


That's how you feel, yes. I'm in tears.



tvad said:


> I have _never_ disputed your knowledge or learning. It's sad that you cannot use your knowledge to bring people together into your discussions, but rather choose vinegar over honey.


A matter of style. Yes, I'm not a touch-feely kind-of-guy, and, yes, I really couldn't care less how many people in this forum love me. Absolutely, nobody can accuse me of trying to make a lot of friends here. I like spicy, you like sweet. So?



tvad said:


> You simply lack any tact or social skills in your posts.


Ahh, you may find this to not be true, but in ways that you may not see immediately.



tvad said:


> In the end, if posting on RBR and displaying an aggrandizing sense of superiority is what it takes to make your day complete, then have at it.


Now that's just a bad analysis.


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## velodog (Sep 26, 2007)

Pirx said:


> I understand the role of the idea in marketing, but why would a cyclist get all up in arms if somebody questions the stiffness myth? What's the reason for that?


Probably spent $5000 to $15000 on the stiffest bestest bike.


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## Pirx (Aug 9, 2009)

Fireform said:


> If we can agree that the force being applied by the rider can be resolved into forces directed to the drivetrain, in the plane of pedal rotation, and forces directed laterally that cause the frame to load and unload,


Trouble is, we cannot agree on such a simplistic view; not if we want to have any hope of understanding reality in this case, that is. The "forces directed to the drivetrain" indeed also "cause the frame to load and unload".



velodog said:


> Probably spent $5000 to $15000 on the stiffest bestest bike.


That's my suspicion, yes.



goodboyr said:


> Cervelo instrumented a bike to try to correlate stiffness and vibration measurements with rider feel. Separately, before he was with cervelo, Damon rinard attempted to estimate energy losses due to stiffness. That's all.


So what did he find? Where can I look up his results?


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## Fireform (Dec 15, 2005)

Pirx said:


> Trouble is, we cannot agree on such a simplistic view; not if we want to have any hope of understanding reality in this case, that is. The "forces directed to the drivetrain" indeed also "cause the frame to load and unload".
> 
> 
> 
> ...


Please quote me correctly. Two of those quotes are from other posters.


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## goodboyr (Apr 19, 2006)

Pirx said:


> Trouble is, we cannot agree on such a simplistic view; not if we want to have any hope of understanding reality in this case, that is. The "forces directed to the drivetrain" indeed also "cause the frame to load and unload".
> 
> 
> 
> ...


http://www.sheldonbrown.com/rinard/fea.htm

Where the 4% estimate comes from.


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## Pirx (Aug 9, 2009)

Fireform said:


> Please quote me correctly. Two of those quotes are from other posters.


Huh? In my browser every one of the quotes is labeled by the author of same. What software are you using to read the forum.


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## ibericb (Oct 28, 2014)

goodboyr said:


> Finite Element Structural Analysis: A New Tool for Bicycle Frame Design, by Leisha A. Peterson and Kelly J. Londry
> 
> Where the 4% estimate comes from.


That's a 1986 FEA of a Trek 770 frame. The 4% is "energy stored" in flexing the frame. That says nothing about the recovery of that energy. As the authors noted:

_"The true intent of a stiff frame is to transfer energy efficiently from the cyclist to the rear wheel. This implies that the designer should minimize the amount of energy that goes into flexing (straining) the frame. *Some of this strain energy might be recoverable (i.e., released in such a way as to add power to the rear wheel). But we know of no measurements that show how much is recovered.* Thus, we assume that the best policy is to minimize strain energy absorption in the frame."_​
In other words, their simulation showed how much energy would be absorbed, but gave no indication of how much of that would be returned to propulsive power, and further the authors stated they have no clue how much that would be.

Hopefully Cervelo did something more insightful?


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## stevesbike (Jun 3, 2002)

Pirx said:


> Oh please. I said that the myth (the claim that stiffer frames are universally advantageous, regardless of rider and riding scenario) should be abandoned because it is a myth. If there's no evidence for or against it, that's what it is.
> 
> 
> 
> ...


You are talking nonsense. I noticed you didn't reply to my impugning your lack of knowledge regarding logic. It's clear now why: you are just making things up and seem driven by some irrational need to prove some point. There's nary a logical thought in your spouting off. You include physics terms in an attempt to obfuscate, and I suspect you don't really understand what you are saying. 

Unfortunately, you also seem to lack any knowledge of the engineering attempts to actually model this issue. Damon Rinard and others at Cervelo represent the best case for attempting to do so. They found that frames store .3-4% of applied power. They found that the stiffest frame they test about halved this stored energy. The entire question of this thread is whether that stored enrgy is returned or not and how that translates into forward motion. If the frame stores less energy, then there's less reason to model how and whether it returns that energy. That's why it's the limiting case and why a stiff frame is the simplest and most straightforward system to model. Perhaps you need a primer on the underlying issues?


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## Pirx (Aug 9, 2009)

goodboyr said:


> Finite Element Structural Analysis: A New Tool for Bicycle Frame Design, by Leisha A. Peterson and Kelly J. Londry
> 
> Where the 4% estimate comes from.


Looked at the article. This says absolutely nothing about energy losses. Those 4% are a number for what the authors call _stored energy_, which is the potential energy stored in the elastic deformation of the frame. I'm not sure who exactly misunderstood what here, but this has next nothing to do with the topic of this discussion.

P.S.: Oops, sorry iberic, I just now saw your parallel post. Oh well.


----------



## Pirx (Aug 9, 2009)

stevesbike said:


> You are talking nonsense.


Interesting. You would not be able to specify exactly what part of my response is nonsense, and why, now, would you?



stevesbike said:


> I noticed you didn't reply to my impugning your lack of knowledge regarding logic.


You did? I'm inconsolable, I must have somehow missed that. Good thing you know exactly why I did not respond.

On the other hand, would you like to go back and answer the questions I had asked you? That's a rhetorical question, of course, because you will not, for reasons I understand only too well. I suspect you do, too. See my previous response to you. Anybody want to place a bet as to whether or not you will answer my questions to you in this post?



stevesbike said:


> You include physics terms in an attempt to obfuscate, and I suspect you don't really understand what you are saying.


Ah, you "suspect" so, do you? Would you be able to demonstrate my lack of understanding, by any chance? 



stevesbike said:


> Unfortunately, you also seem to lack any knowledge of the engineering attempts to actually model this issue. Damon Rinard and others at Cervelo represent the best case for attempting to do so. They found that frames store .3-4% of applied power.


See mine and iberic's reply to this point. I repeat what I said before: You do not understand what you are talking about. The dated work you so desperately rely on provides nothing to help your case. The idea that because I am unfamiliar with an irrelevant result I would somehow "lack any knowledge of the engineering attempts to actually model this issue" is laughable, to put it mildly. 

By the way, your representation of the findings is completely wrong, starting with the fact that power is not stored, energy is. I'll spare you the embarrassment of explaining exactly how fundamental that error of yours really is, nice guy that I am.



stevesbike said:


> If the frame stores less energy, then there's less reason to model how and whether it returns that energy. That's why it's the limiting case and why a stiff frame is the simplest and most straightforward system to model. Perhaps you need a primer on the underlying issues?


I thought I had explained to you that you are in no position to even begin to grasp the physics of this problem. I will just mention that (a) the analysis you describe is static, and the static case is entirely trivial anyway as far as our topic is concerned, and (b) I had already explained to you that the dynamics of the bicycle-rider system even with a stiff frame is far from simple. I know you are in no position to even begin to understand this point, see below. Somebody in your position offering someone like me a primer on the "underlying issues" is hilarious. You do love to make a fool of yourself, do you? But, by all means, feel free to produce the primer you're so generously offering to me. Why do I have the feeling that primer may not be forthcoming?

And, to respond to my good friend tvad's missive on that topic, me saying this has nothing to do with arrogance. In fact, this reminds me of the time, a few decades ago, when as a fresh PhD student I asked one of our math professors about some idea I was excited about. I will never forget how he looked at me curiously, and then said: "Wellll, in order to [understand this problem] you will first have to learn the math". I was hurt by the answer at the time, and did find it a bit arrogant, noting, however, that the guy I had asked this question was one of the world's top authorities in dynamical systems theory, so him looking down on a young PhD student may seem not so inexcusable after all. Anyway, with what I know today, I fully understand what he was saying, and why he was saying it: Without the knowledge that he urged me to acquire, there was no way for me to even begin to understand any pertinent answer he could give me. You, my friend, are in the same situation as this younger me: In order to understand what I am saying, you would first have to learn some analytical mechanics. Without that, I am just wasting my time with you.


----------



## myhui (Aug 11, 2012)

Pirx said:


> You, my friend, are in the same situation as this younger me: In order to understand what I am saying, you would first have to learn some analytical mechanics.


How about I attempt a one sentence clarification: if that frame flexes a little, then it's true that you will transfer less energy to the bike on that pedal stroke compared to a stiffer frame, but note that you did transfer less energy, so nothing's lost, since your muscles also produced slightly less energy too.


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## aclinjury (Sep 12, 2011)

Pirx said:


> .......
> 
> ....In fact, this reminds me of the time, a few decades ago, when as a fresh PhD student I asked one of our math professors about some idea I was excited about. I will never forget how he looked at me curiously, and then said: "Wellll, in order to [understand this problem] you will first have to learn the math". I was hurt by the answer at the time, and did find it a bit arrogant, noting, however, that the guy I had asked this question was one of the world's top authorities in dynamical systems theory, so him looking down on a young PhD student may seem not so inexcusable after all. Anyway, with what I know today, I fully understand what he was saying, and why he was saying it: Without the knowledge that he urged me to acquire, there was no way for me to even begin to understand any pertinent answer he could give me. You, my friend, are in the same situation as this younger me: In order to understand what I am saying, you would first have to learn some analytical mechanics. Without that, I am just wasting my time with you.


I don't remember where I read this from years ago, but an article discussed one issue in the US Air Force. The issue was/is that the all the hightech whiz-bang jet fighters are designed by guys PhDs, operated by BS,...and maintaned by high school diplomas. It is clear in this thread thusfar that you and ibericb are operating at the PhD level, while the rest appear to be on the highschool physics level. The problem arises not only due to a lack of communication (due to limitation of language) but also due to a lack of a common ground of knowledge (the Air Force mechanic cannot hope to understand what the PhDs are saying when it comes down to discussing a real technical issue). I feel this thread is that, but I admit it's sort of entertaining watching the flow of the discussion!


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## Pirx (Aug 9, 2009)

aclinjury said:


> The problem arises not only due to a lack of communication (due to limitation of language) but also due to a lack of a common ground of knowledge (the Air Force mechanic cannot hope to understand what the PhDs are saying when it comes down to discussing a real technical issue).


That's a good analogy, yes.



aclinjury said:


> I feel this thread is that, but I admit it's sort of entertaining watching the flow of the discussion!


It's been our pleasure... :wink:


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## goodboyr (Apr 19, 2006)

I'm not arguing with you. You asked for the reference where the famous 4% number that everyone is quoting came from. I gave you the reference. I doubt there is any way to experimentally determine how much energy is returned. There's too much uncertainty with power meter measurement and there are too many other extraneous factors.


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## goodboyr (Apr 19, 2006)

This discussion seems to be similar to a person in the boxing ring wanting to take on all others in a fight. For all the phd's in the room, there's not much patience for teaching, but a lot of time for putting down those who disagree or don't understand.


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## robt57 (Jul 23, 2011)

goodboyr said:


> I'm not arguing with you.



Of course you are, we all are, everybody is. It is air apparent just looking at all the replies made to even the most of reasonable posts.

Unless like stiffness/imagination, this too is imagination... Who's imagination, I am not sure..

What I find particularly annoying, and did right off, is the total self absorbed gratification trolling trolling in conversational guise. 

Don't bother a reply to this, you will not make me feed the troll any more. It is not even a trolling on the subject anymore, only the ego fanning.

I am reminded of a line from the movie 'The Heist' para phrasing: "Everybody has the right to be a pain in the ass but you abuse the privilege"

All due respect [if any is due] MEH!


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## myhui (Aug 11, 2012)

robt57 said:


> All due respect [if any is due] MEH!


Let it DERP.


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## goodboyr (Apr 19, 2006)

robt57 said:


> Of course you are, we all are, everybody is. It is air apparent just looking at all the replies made to even the most of reasonable posts.
> 
> Unless like stiffness/imagination, this too is imagination... Who's imagination, I am not sure..
> 
> ...


Not sure what I did to deserve this. In any case, I've asked moderator to intervene.


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## robt57 (Jul 23, 2011)

goodboyr said:


> Not sure what I did to deserve this. In any case, I've asked moderator to intervene.


I did not mean to target you and no you don't deserve a dis. My apologizes if mis- directed by me contextually. More an attempt to carry the idea, no need to tell Mommy! 

More a bit of sarcasm, and the MEH is directed to the actually trolling and not your posts.

Again, apologies if quoting your message gave you the idea I made a target out of you and your post.


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## goodboyr (Apr 19, 2006)

OK. Understood and thanks for the clarification.

This thread is crying for moderator involvement. That's not crying to "mommy". People clearly don't realize how insulting they are, and how it turns others off from participating and learning. So, in that particular case, I respectfully disagree.


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## robt57 (Jul 23, 2011)

goodboyr said:


> This thread is crying for moderator involvement. That's not crying to "mommy".


My little attempt a at some humor 'telling mommy'. I probably only crack myself up. I think you gotta do something really really bad here to get an intervention, just observation-ally.

Peace, and again my bad..


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## Trek_5200 (Apr 21, 2013)

The bike I ride is not the stiffest available yet in no way is the frame slowing me down, but tracks well and is comfortable. The whole stiffness flexing thing applies to bikes from a generation or so ago when riders did witness flexing. A subset of the older steel bikes I seem to recall.


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## cxwrench (Nov 9, 2004)

I do find it a little weird that one of the things that has remained constant in the industry for the last 50 years has been the quest for 'stiffer' frames. This has been the case since the 60's. Steel tubesets were designed and engineered to be stiffer over the years, then aluminum tubes came along. Same thing happened with them. Then carbon. Don't forget titanium... Nothing at all has changed since then. Every single manufacturer strives to accomplish this. Is it actually true that every single one of them is wrong, and only does this for marketing purposes? Not one of them has attempted to call the others out on this premise? Instead every last one of them is on the exact same path. 


Weird, huh? Maybe Pirx should send a mass email to every manufacturer and let them know how much money they're wasting and how they're taking all of us for fools. He could enlighten them to the fact that we're in on their little secret...that we now know the truth!


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## goodboyr (Apr 19, 2006)

robt57 said:


> My little attempt a at some humor 'telling mommy'. I probably only crack myself up. I think you gotta do something really really bad here to get an intervention, just observation-ally.
> 
> Peace, and again my bad..


Thanks.


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## Pirx (Aug 9, 2009)

You have a good point there, but I think there's at least two answers that partially explain the situation. The first one is marketing, and that has been discussed before. The second one is that this particular piece of lore somehow seems to resonate, on an intuitive level, with the bicycle-buying public, so why not go for it. 

Given that additional stiffness, no matter what it does, will lead to only minuscule changes in the performance of a frame (that are so small as to be essentially impossible to measure), what's there to lose? Let's just go with the theme, and if it helps sell bikes, which it very clearly does, why would any manufacturer give a rat's behind what the real story is?


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## ibericb (Oct 28, 2014)

robt57 said:


> ... *It is air apparent *just looking at all the replies made to even the most of reasonable posts. ...


Air apparent? What does that mean?


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## myhui (Aug 11, 2012)

Pirx said:


> Given that additional stiffness, no matter what it does, will lead to only minuscule changes in the performance of a frame (that are so small as to be essentially impossible to measure), what's there to lose?


Psychological superiority.


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## robt57 (Jul 23, 2011)

ibericb said:


> Air apparent? What does that mean?



If it walks like a duck, but more on the line if the olfactory. As in, if you stepped in it, and smell it [air] it is apparent you stepped in it...

Pardon my slang. Something my old pappy used to say...


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## cxwrench (Nov 9, 2004)

Pirx said:


> You have a good point there, but I think there's at least two answers that partially explain the situation. The first one is marketing, and that has been discussed before. The second one is that this particular piece of lore somehow seems to resonate, on an intuitive level, with the bicycle-buying public, so why not go for it.
> 
> Given that additional stiffness, no matter what it does, will lead to only minuscule changes in the performance of a frame (that are so small as to be essentially impossible to measure), what's there to lose? Let's just go with the theme, and if it helps sell bikes, which it very clearly does, why would any manufacturer give a rat's behind what the real story is?


Because they have with other parts of the bike? Tire pressure/size for example. Drivetrain gearing for another. The industry has finally admitted that lower pressure/larger tires work better. The industry is now ok w/ compact chainrings and wide range cassettes, even pro racers use them. They've realized that not everyone fits on a 'racers' geometry. I find it hard to believe that all these engineers cost their respective companies tons of money while they follow their mission of making bikes more and more 'laterally stiff/vertically comliant' and it's just a marketing exercise. The guys that sign the paychecks would see through that in an instant.


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## Father Guzzi Obrian (Jan 31, 2015)

Pirx said:


> Trouble is, we cannot agree on such a simplistic view; not if we want to have any hope of understanding reality in this case, that is. The "forces directed to the drivetrain" indeed also "cause the frame to load and unload".
> 
> 
> 
> ...



I am enjoying this thread, and as a simpleton, I can add my perspective. I have a Spec Roubaix SL2 and a Trek Domane, both with similar Ultegra bits. I bought the Trek because the Roubaix seemed slow, the Trek is faster and more comfortable. I believe the Roubaix was losing something in the fittings on the forks and the chain stays while the Trek was not losing with its isolation strategy, just my observation over many miles back to back on both of these bikes, so it is probably worth little to this conversation, but perhaps....


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## duriel (Oct 10, 2013)

If you're strong you need a stiff bike. If you're strong and on a wiggle, you may have the ability put out all the power in the world, but only the wiggle is going to limit the amount of force delivered to the wheel. It is just that simple. 
The energy/power is not lost it is never generated as there is nothing to push against.


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## ibericb (Oct 28, 2014)

cxwrench said:


> I do find it a little weird that one of the things that has remained constant in the industry for the last 50 years has been the quest for 'stiffer' frames. ...


That does pretty much seem to be the case. A very plausible explanation comes from the evolution noted in the BQ blog noted in the original post. (this one). 

As Jan Heine explains it was a misguided notion (stiffer frame = better performance) that originated in the evolution of steel tube alloys, and subsequently carried over when newer materials began to appear in the 1980's. The new materials offered even lower weight with "increased stiffness", which was being sought at the time via high strength steel tubesets (not necessarily stiffer frames). It became a point of differentiating frames with newer materials from the then favored high strength steel alloys of the time, and it was a feature well marketed, right or wrong, that helped sell more bikes.

My view is that there is an optimum stiffness for every cyclist in a given cycling scenario. The issue is that there is no good way to determine that other than rider experience. The problem has eluded a definitive solution due largely to it's complexity and the great variability of cyclists and situations. In the absence of a definitive ability to specify optimal stiffness the notion that stiffer = better performance continues because it's what the buying market has long been led to believe.


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## Pirx (Aug 9, 2009)

cxwrench said:


> Tire pressure/size for example.


I think, for a long time (virtually from the early days of bicycle racing up until very recently) everybody really believed that narrower tires are faster. You can see the analogy, I'm sure... 



cxwrench said:


> I find it hard to believe that all these engineers cost their respective companies tons of money while they follow their mission of making bikes more and more 'laterally stiff/vertically compliant' and it's just a marketing exercise. The guys that sign the paychecks would see through that in an instant.


You need to understand that these engineers are directed to develop such frames by the guys who sign the paychecks, counseled by their marketing departments. As many practicing engineers know, the engineer isn't always asked first... 

And, it's not "just a marketing exercise"; it's a proven moneymaker. Tell people that the newest frame you have is "30% stiffer" and therefore "performs better", and people will dump last year's frames in droves, and flock to buy the new one. Again, from the company's perspective, what's not to like?


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## cxwrench (Nov 9, 2004)

Pirx said:


> I think, for a long time (virtually from the early days of bicycle racing up until very recently) everybody really believed that narrower tires are faster. You can see the analogy, I'm sure...
> 
> 
> 
> ...


It makes sense to me that at some point an engineer (they have to be included in meetings at some point, and they can email/talk to whomever they want to) would let the product manage know that it was all BS and they could save money by not spending money on it.


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## Pirx (Aug 9, 2009)

cxwrench said:


> they could save money by not spending money on it.


But the point is that they are actually _making_ money, lots of it, by perpetuating the myth. In other words, the money invested in these stiffer frames does pay off, despite the fact that there's no performance benefit. There's very real benefits in sales.


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## cxwrench (Nov 9, 2004)

Pirx said:


> But the point is that they are actually _making_ money, lots of it, by perpetuating the myth. In other words, the money invested in these stiffer frames does pay off, despite the fact that there's no performance benefit. There's very real benefits in sales.


Exactly...if it's the marketing dept's baby, then market the **** out of it. Just don't bother w/ the engineering.  Who's gonna know?


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## ibericb (Oct 28, 2014)

cxwrench said:


> Exactly...if it's the marketing dept's baby, then market the **** out of it. Just don't bother w/ the engineering.  Who's gonna know?


Having spent 25 years in a very large corporation where the R&D tech guys and the marketing guys were frequently at odds, what often happens is the engineers and tech types will say something like, "but this is technically better and the right way to go". Then the marketing and business guys, respond with something like " we got it, but we can't sell that, certainly not in the face of competitor X". It's a very common conversation. What gets developed is what the commercial folks believe will sell, at least most of the time (the Edsel was a clear exception).


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## myhui (Aug 11, 2012)

A similar issue exists with automobile wheel diameter. Bigger isn't always better. But marketing says bigger will sell better. So bigger it is.

The S2000 in my garage has stock front
tires with size 205/55 R16. The engineers won that argument, since 16" diameter is unfashionably small.


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## stevesbike (Jun 3, 2002)

Pirx said:


> Interesting. You would not be able to specify exactly what part of my response is nonsense, and why, now, would you?
> 
> 
> 
> ...


Again, your rants are just a babble of fallacies, particularly appeal to authority. It's an Internet Forum - you can state that you have all the expertise you want, but unless you actually demonstrate it, who cares? And, likewise, you don't know the expertise of others, so insulting people doesn't help your position, which so far has been based on subjective rider preferences of a limited sample. The fact is, the majority of riders prefer a frame with a stiff BB.

As for your insult about what I said about power, again you are talking nonsense. The entire point of your rant is about rate of energy, watts, put into a frame, which will require estimating applied power, frame deflection, and cadence. 

All the hysteria you generate in your ad hominen screeds also obscures the fact that the question of how much energy is lost, returned, and whether the returned energy translates into forward motion depends on determining what angular crank range does the frame strain up and during what angular crank range does the frame unstrain.

And, once again, this has been empirically measured and found that the returned energy is not in phase to help with the opposite leg applied power. 

Whether the lost energy is negligible or not is another issue. But don't simply obfuscate with histrionics.


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## PBL450 (Apr 12, 2014)

Pirx said:


> If some of the energy input by the rider is used to temporarily flex the frame, once the frame un-flexes the energy is returned. All of it. No energy is lost. None. At. All.


Irrelevant, but exact same thing and exact same phenomenon in speed skating frames. Rider preference on flex... No effect of performance.


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## PBL450 (Apr 12, 2014)

goodboyr said:


> Not sure what I did to deserve this. In any case, I've asked moderator to intervene.


You missed it completely... His post may have wandered all over the place. But it wasn't in any way aiming an attack at you. Mods? Really? HTFU. Jeez.


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## goodboyr (Apr 19, 2006)

Didn't involve you. Read the thread. All good now.


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## PBL450 (Apr 12, 2014)

Pirx said:


> I think, for a long time (virtually from the early days of bicycle racing up until very recently) everybody really believed that narrower tires are faster. You can see the analogy, I'm sure...


Huh? Wait... You lost me here... Earlier you said weight and aero were real and had actual impacts? A 32 vs a 23 Conti can be 1/2 pound difference. half a pound is a lot in cycling world. And the aero difference between a 32 and 23? Maybe insignificant, I don't know. But that bigger tire is much heavier. Rolling resistance being equal,,wouldn't the 23 be a clear winner? The 32 would have to have significantly better rolling resistance? Isn't lighter faster? At least climbing, which is where we spend a lot (most?) of our time if we live with hills...


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## Pirx (Aug 9, 2009)

stevesbike said:


> Again, your rants are just a babble of fallacies, particularly appeal to authority. It's an Internet Forum - you can state that you have all the expertise you want, but unless you actually demonstrate it, who cares? And, likewise, you don't know the expertise of others, so insulting people doesn't help your position, which so far has been based on subjective rider preferences of a limited sample. The fact is, the majority of riders prefer a frame with a stiff BB.
> 
> As for your insult about what I said about power, again you are talking nonsense. The entire point of your rant is about rate of energy, watts, put into a frame, which will require estimating applied power, frame deflection, and cadence.
> 
> ...


I have no further comments to you.


----------



## tvad (Aug 31, 2003)

Pirx said:


> I have no further comments to you.


After 6 pages and 29 posts from Prix, it comes to this.

stevesbike for President. Kudos sir!


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## myhui (Aug 11, 2012)

My bicycle frame is soft, mom, my bicycle frame is soft ...


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## aclinjury (Sep 12, 2011)

stevesbike said:


> Again, your rants are just a babble of fallacies, particularly appeal to authority. It's an Internet Forum - you can state that you have all the expertise you want, but unless you actually demonstrate it, who cares? And, likewise, you don't know the expertise of others, so insulting people doesn't help your position, which so far has been based on subjective rider preferences of a limited sample. The fact is, the majority of riders prefer a frame with a stiff BB.
> 
> As for your insult about what I said about power, again you are talking nonsense. The entire point of your rant is about rate of energy, watts, put into a frame, which will require estimating applied power, frame deflection, and cadence.
> 
> ...


conservation of energy (and mass), if energy is lost, then somewhere mass has been altered. A fundamental concept in physics.

Also, just because the majority of people want a stiffer bb, it doesn't mean they really understand what they want. A lot of their want is organized marketing pushed down their throat. I've ask you (and others) in this forum before, is there ever a case that an argument can be clearly made that it's frame stiffness that makes the difference in winning and losing? Not one person has been able to make such an argument, yet... they all will swear by frame stiffness. See what I mean, sometimes the public doesn't know jack about the science, but they know plenty of marketing literatures. But frame stiffness will soon be an old argument, because the current hot topic is "aero".


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## PBL450 (Apr 12, 2014)

myhui said:


> My bicycle frame is soft, mom, my bicycle frame is soft ...


Kinda creepin me out again...


----------



## Pirx (Aug 9, 2009)

PBL450 said:


> Huh? Wait... You lost me here... Earlier you said weight and aero were real and had actual impacts?


Yes, sorry, this is not a perfect analogy. The point of similarity is only that for many, many years _everybody_ knew that narrower tires are faster, just like now everybody assumes that stiffer bikes are more efficient. In both cases, it turns out that what everybody knew was false. Heck, with the tires I remember running an 18mm Conti clincher in the front in the 1980s. Of course, as you allude to, the picture with tires is complex, but it's reasonably well understood. There's tradeoffs between weight, aerodynamics, and rolling resistance. Bottom line is that running wider tires can make sense in some cases.



tvad said:


> After 6 pages and 29 posts from Prix, it comes to this.


I don't think you understood what it is "it" has come to. Hint: read my previous response to the gentleman, and then assess how he responded, or rather declined to respond.



aclinjury said:


> But frame stiffness will soon be an old argument, because the current hot topic is "aero".


Well, that topic at least has relevance for performance. Frame stiffness does not, as far as we know.


----------



## tvad (Aug 31, 2003)

Pirx said:


> I don't think you understood what it is "it" has come to. Hint: read my previous response to the gentleman, and then assess how he responded, or rather declined to respond.


I don't think you understand that the meaning of "it" doesn't matter. The fact that for one glorious moment stevesbike's comment halted your derisive bloviation is what matters.


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## Pirx (Aug 9, 2009)

cxwrench said:


> Exactly...if it's the marketing dept's baby, then market the **** out of it. Just don't bother w/ the engineering.  Who's gonna know?


Sorry, forgot to reply to this one: The problem with your suggestion is that stiffness is fairly easy to measure, so there's a good chance somebody will find out. If a cycling magazine happens to do that and catches you red-handed, you'd be in big trouble. But, of course, you're probably right: For the riders it's impossible to notice. They'll still tell you how much stiffer and more efficient the bike feels no matter what...


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## myhui (Aug 11, 2012)

"You can sell a soft bicycle frame to a woman, but you cannot sell a soft bicycle frame to a man."

(triple face palm ...)


----------



## tvad (Aug 31, 2003)

^ Does anyone have a secret decoder ring to explain what myhui is talking about in this thread?


----------



## Blue CheeseHead (Jul 14, 2008)

Pirx said:


> If some of the energy input by the rider is used to temporarily flex the frame, once the frame un-flexes the energy is returned. All of it. No energy is lost. None. At. All.


That statement is scientifically incorrect. Some energy in an elastic system is lost to heat. 

Secondly, flexing of a frame can create mis-alignments within the drivetrain that results in additional friction. An extreme case would be the chain rubbing the front derailleur at certain points of the pedal stroke.


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## stevesbike (Jun 3, 2002)

tvad said:


> After 6 pages and 29 posts from Prix, it comes to this.
> 
> stevesbike for President. Kudos sir!


thanks - isn't it interesting what happens to someone like Pirx, who tries to dominate a thread by relying on bloated rants stringing together fallacies and insults when they are confronted by someone who actually knows what they are talking about, has more scientific credentials, and sees through their sophomoric tactics. When they can no longer control the narrative, they suddenly have no response, despite the fact that they seem to spend hours in these forums. Classic case of confirmation bias and interested in hearing only those replies that support their own biases and not actual debate. It's particularly ironic that he wants to revisit what's the deadest of dead horses - bb stiffness and efficiency. For anyone who wants to read what actual engineers/scientists have to say about this, check out slowtwitch forums with Jack Mott, Damon Rinard, et al.


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## robt57 (Jul 23, 2011)

stevesbike said:


> thanks - isn't it interesting what happens to someone like Pirx, who tries to dominate a thread by relying on bloated rants stringing together fallacies and insults when they are confronted by someone who actually knows what they are talking about, has more scientific credentials, and sees through their sophomoric tactics. When they can no longer control the narrative, they suddenly have no response, despite the fact that they seem to spend hours in these forums. Classic case of confirmation bias and interested in hearing only those replies that support their own biases and not actual debate. It's particularly ironic that he wants to revisit what's the deadest of dead horses - bb stiffness and efficiency. For anyone who wants to read what actual engineers/scientists have to say about this, check out slowtwitch forums with Jack Mott, Damon Rinard, et al.



Thanks for typing that for me. We muggles just are not up to the task in the company of such genius as P_r_. [nudge nudge wink wink].

So much for the Thumper doctrine...


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## ibericb (Oct 28, 2014)

stevesbike said:


> It's particularly ironic that he wants to revisit what's the deadest of dead horses - bb stiffness and efficiency. For anyone who wants to read what actual engineers/scientists have to say about this, check out slowtwitch forums with Jack Mott, Damon Rinard, et al.


Like this thread, from which the following is excerpted?

From jackmott: _"I think the basic conclusion was that stiffer usually won't make you any faster but it will feel better. 

For instance in a TT scenario, you will be putting pretty close to no energy into the frame anyway. If you really mash it, you get a fair amount of energy into the frame but you get most of it back. "_

From jbsurfin: _"Yes, Damon pretty much conceded there was no power loss in frame/bb flex. Kudos to him for telling the truth and not spinning some misinformation."_​
The prior postings from Rinard that Mott, et al were referring to are in this thread on BBright. In that it becomes clear that Rinard's assessment is from an FEA model (which is a methodology referenced previously that you took issue with), and the range of "power stored" is from 0.3% for "cruising" up to 4% for "out-of-saddle climb". He is later challenged on the use of the word power, and corrects it to energy. Late in that thread the question of returning stored energy to propulsive power was addressed.


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## Pirx (Aug 9, 2009)

stevesbike said:


> thanks - isn't it interesting what happens to someone like Pirx, who tries to dominate a thread by relying on bloated rants stringing together fallacies and insults when they are confronted by someone who actually knows what they are talking about, has more scientific credentials, and sees through their sophomoric tactics. When they can no longer control the narrative, they suddenly have no response, despite the fact that they seem to spend hours in these forums. Classic case of confirmation bias and interested in hearing only those replies that support their own biases and not actual debate. It's particularly ironic that he wants to revisit what's the deadest of dead horses - bb stiffness and efficiency. For anyone who wants to read what actual engineers/scientists have to say about this, check out slowtwitch forums with Jack Mott, Damon Rinard, et al.


Whoah, now, this is fascinating! You actually have the chutzpah to come back in here, after having ducked every single question I had asked you on the topic? You have the gall of pretending that you have the slightest clue of what you are talking about on this topic? You claim to have "more scientific credentials", without revealing what those might be, of course? Then, to top it all off, you babble about "sophomoric tactics"? Finally, your ultimate reference on this are the slowtwitch forums? Are you for real?

But no matter, let's just take that cute little rant of yours at face value. Why don't you demonstrate to us exactly why, and how, frame flex must lead to loss of efficiency even while neglecting material damping. Come on, don't be shy, fame and fortune are waiting for you, given that so far nobody has managed to do this.

Here's a little help on that topic:
On material damping, typical materials used in frame building have hysteresis losses for the static case that are significantly less than 1%. Let's make it 1%, and let's observe that energy stored on frame flex during the pedaling cycle is around 1% also. There was a number of 4% quoted earlier but I think that's on the high side, see here. Nevertheless, let's stay with that 4% number, then we find that about 0.04% of input power may get converted to heat. At 300W, that would be about 1 tenth of a Watt, which is so tiny as to completely be swamped by the noise.

Second, on the problem of understanding the effect of frame deformation on pedaling efficiency of the rider, I found this old preprint by a postdoc of one of my former colleagues in my collection. You might want to read up a little bit on the "minor" task of modeling cycling efficiency before you start snowing anyone in here with your illiterate drivel.
I must say that I had completely forgotten about that paper, but the final paragraph in that manuscript seems prescient of this debate, and is worth quoting:



> While riders insist that bicycle flexibility reduces pedaling
> efficiency through Joss of the stored elastic energy, conservation-of-
> energy arguments indicate that there is generally no such loss.
> As well, cyclists seem to be inconsistent in their perceptions and
> ...


Oh, and let's set this one straight: You have no training, of any kind, in any of the pertinent sciences (including engineering sciences). None. At. All. You have no idea of the hilarity you created with that silly little post of yours. Thanks for that one!


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## Pirx (Aug 9, 2009)

While we enjoy watching my good friend Stevie squirm and cook up some interesting sophistry to hide his ignorance (no, really, I am starting to enjoy this show... :aureola, here is a constructive suggestion: One way in which differences in cycling efficiency could be demonstrated is by instrumenting different bikes (different frame, ideally, all the rest identical) with both a crank-based and a hub-based powermeter, and see what, if any differences we can find. This is not a perfect test, mind you, since it will entirely ignore the biomechanics side of the problem, but it would be a very simple experiment to perform, in principle. This test should at least help put some of the misconceptions swirling around the topic to rest.


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## ibericb (Oct 28, 2014)

Let me pinpoint this comment from Rinard in the second slowtwitch thread previously referenced, in response to the question, "what's a good repeatble way to test this (power savings) in the field?" Rinard tesponded:

_"I wouldn't expect to find significant results with any physical testing procedure I'm aware of. In my opinion the numbers are too small to reliably detect today; instead, I'd focus on something else to make me go faster. 
Damon Rinard 
Engineering Manager, 
Cannondale Road Engineering Department 
Since 2015 "_


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## HFroller (Aug 10, 2014)

I had training in some of the pertinent sciences, and I find this discussion more amusing by the day. Particularly amusing is the final paragrap of that "old preprint" by a postdoc. 

The first three lines basically say this: "if you can't store elastic energy in a frame, then you can't store elastic energy in the frame". 

Well, yes. Very true. Really an insightful statement Postdocs are famous for them. Did this "old preprint" ever get printed?


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## Pirx (Aug 9, 2009)

HFroller said:


> The first three lines basically say this: "if you can't store elastic energy in a frame, then you can't store elastic energy in the frame".


Please explain your most interesting translation of the sentence "While riders insist that bicycle flexibility reduces pedaling efficiency through loss of the stored elastic energy, conservation-of-energy arguments indicate that there is generally no such loss", if you will. Thank you.

Published in 1987 in an ASME volume on Biomechanics in Sports. See the article itself, if you can be bothered. This is material from Andy Ruina's website, just in case you're interested. If you know anything at all about the field, then this should be all I need to tell you. You're welcome.

P.S.: Oh, and by all means, humor us by letting us know what specifically you find amusing about this debate.

P.P.S.: By the way, "training in some of the pertinent sciences" can mean many things, as I am sure you know. Specifically, if you want to be able to contribute productively to this discussion, you should at least be able to follow the kind of formalism laid out in this introductory material. Please note, this is not a complete treatise, it's just meant to showcase the mathematical machinery that's required. The question is just if you are familiar with the formalism.


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## ibericb (Oct 28, 2014)

Pirx said:


> here is a constructive suggestion: ...


I had that thought several days ago, but dismissed it as I suspect the precision afforded by relative power measurements would not be up to the task of discerning the differences even in an idealized system. Put a real person on the cranks, then I just can't see it being a productive effort at all. But if someone has the time and money, I wouldn't try to talk them out of it.


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## Pirx (Aug 9, 2009)

ibericb said:


> I had that thought several days ago, but dismissed it as I suspect the precision afforded by relative power measurements would not be up to the task of discerning the differences even in an idealized system.


Oh, no doubt, there is no equipment that can confirm that the difference is exactly zero. Nevertheless, I know that SRM sells a "science" version of their powermeter (for $5k or so, I think) that has accuracy better than 0.5%. If we get that kind of accuracy, and if we can show that the difference, if it exists, must be less than, say 0.5% (I note in passing that with some smart data analysis, we may be able to increase the precision of such a statement a bit, perhaps to 0.1%), then that's progress.


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## cxwrench (Nov 9, 2004)

ibericb said:


> Let me pinpoint this comment from Rinard in the second slowtwitch thread previously referenced, in response to the question, "what's a good repeatble way to test this (power savings) in the field?" Rinard tesponded:
> 
> _"I wouldn't expect to find significant results with any physical testing procedure I'm aware of. In my opinion the numbers are too small to reliably detect today; instead, I'd focus on something else to make me go faster.
> Damon Rinard
> ...


Rinard has always impressed me as being much more concerned w/ aerodynamics than 'stiffness'. And he seems to think ride quality is important as well. I've been to Brain Bike (Cervelo's dealer brainwashing conference) and he did a decent job of getting the idea across to dealers in a way they could understand.


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## Pirx (Aug 9, 2009)

robt57 said:


> Thanks for typing that for me. We muggles just are not up to the task in the company of such genius as P_r_. [nudge nudge wink wink].


Dude, you're betting on the wrong horse. Just sayin'. But, I understand that just watching is half the fun, right? :devil:


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## davidka (Dec 12, 2001)

I'm always fascinated by how much importance riders place on frame stiffness. I've always found the BB of any frame I've ridden adequate (the only time I experienced F/D rub was in the square-taper BB days, mostly in the crank system). 

Here's something fun to do- wrap your fingers around the outside of the seat-stay on your frame, and place your thumb on the opposite side of the rear wheel. Now press on the side of the rim and with your thumb marvel at how flexible your rear wheel is. 

All frames are stiff enough. The idea of energy loss in the frame is debatable, but ultimately the debate is a waste of time. One crank revolution is one crank revolution. The freshest, strongest rider will win the sprint, regardless of what frame he's on.


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## cxwrench (Nov 9, 2004)

ibericb said:


> Years ago Keith Bontrager was well known for his rants about various technical topics in cycling, often maligning the press, marketing, and the like. He would periodically post those in blog format on the old Bontrager site. One of those was a five part series on stiffness, and the merits of stiffness as an attribute for cycling performance. Some of those rants were saved by others. His discourse on stiffness, all five parts in sequence, can be seen here. If you want to cut to the chase, scroll down to "STIFFNESS 5 Stiffness in 3D" near the bottom, and follow his description of a sprinter, and his view of the kind of analysis it takes to appreciate how optimal stiffness can depend upon the rider, where he concludes:
> 
> "_If the short term power at the rear wheel was plotted as a function of stiffness, the optimum may not be found to be at infinite frame stiffness. If the material damping losses are small (any bets?), then a certain amount of flexibility may actually contribute to efficiency in this case. _"​
> I believe Bontrager's description of the sprinter is illustrative of how frame stiffness and rider can interact in complex ways, often unknown to the cyclist. That leads to the conclusion that more stiffness does not always translate into increased performance. A key point that this entire thread began with is to determine what works best for you, and then use that rather than fall victim to the promoted notion that stiffer is necessarily better for more power.
> ...


There might be some similarity here, maybe not. A few years ago Honda, I believe, was developing new MotoGP chassis as usual...development never stops. They were getting stiffer and stiffer in every direction imaginable. It got to a point where the riders couldn't go any quicker and the engineers were certain they should be able to extract some more speed out of the newest, stiffest chassis. But not one of them could lap faster than w/ the old chassis. Since they usually have older models to compare 'feel', they went back to the old chassis w/ the new motor and the riders went faster. The old frame had a little more flex and the riders all agreed that this allowed them to make the most of the power they had. 

So there's that...


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## davidka (Dec 12, 2001)

That was the late 90's. They realized that lateral flex was a key component for cornering traction. They also use a smaller diameter rear wheel (making up the diameter with a taller tire) for the same reason.


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## PBL450 (Apr 12, 2014)

Pirx said:


> Yes, sorry, this is not a perfect analogy. The point of similarity is only that for many, many years _everybody_ knew that narrower tires are faster, just like now everybody assumes that stiffer bikes are more efficient. In both cases, it turns out that what everybody knew was false. Heck, with the tires I remember running an 18mm Conti clincher in the front in the 1980s. Of course, as you allude to, the picture with tires is complex, but it's reasonably well understood. There's tradeoffs between weight, aerodynamics, and rolling resistance. Bottom line is that running wider tires can make sense in some cases..


Thanks. Got dropped there... I'm on the back again, clinging as best I can to the science... 

This debate has been around forever with speed skating frames, 2 point offers flex, comfort etc, 3 point mount offers zero flex... No "lost energy." But that's been long abandoned... It's just a matter of skater comfort and confidence. Some folks like a little bend in the corners on their crossovers, as they generate major accelerations and some people like no flex, solid, predictable and the same through every corner. The fact that performance isn't better or worse is pretty mainstream now, it's just a preference. Some people swear they can lean more, with more confidence, with a hint of flex. Not me. I like predictability. But it's the same argument, just with much simpler systems.


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## HFroller (Aug 10, 2014)

Pirx said:


> P.S.: Oh, and by all means, humor us by letting us know what specifically you find amusing about this debate.
> 
> P.P.S.: By the way, "training in some of the pertinent sciences" can mean many things, as I am sure you know. Specifically, if you want to be able to contribute productively to this discussion, you should at least be able to follow the kind of formalism laid out in this introductory material. Please note, this is not a complete treatise, it's just meant to showcase the mathematical machinery that's required. The question is just if you are familiar with the formalism.


"Conservation of energy" popping up all the time ... That's what is amusing. And no, I'm not going to explain it.

Goldstein more or less from A to Z, that's enough mathematical machinery for you? Actually, it was Goldstein with some mathematics on manifolds added - differential forms etc. A very good text, Goldstein, but a bit old-fashioned. I could add Quantenmechanik und Gruppentheorie by Weyl. Not relevant here, just to show that I recognize nice mathematical machinery when I see it. Or would you like to know more about index theorems for partial differential equations? If you don't know anything about index theorems for PDE's, I rather doubt that you could tell me - or anybody else - something interesting about mathematical machinery.


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## Pirx (Aug 9, 2009)

HFroller said:


> "Conservation of energy" popping up all the time ... That's what is amusing. And no, I'm not going to explain it.


Well, if you know mechanics then this might seem trivial, but it's clearly a concept that's not generally understood, at all. At least the layman very often does not recognize nor understand the farther-reaching consequences of energy conservation principles. Amusing? Perhaps, depending on your point of view. Anyway, that's fine, you and I know there's no explanation since the sentence in question _was_ making a non-trivial statement relative to popular understanding of the question.



HFroller said:


> Goldstein more or less from A to Z, that's enough mathematical machinery for you?


Oh please, let's refrain from trying to enter into a pissing contest that would be utterly meaningless, even to those that understand what we are talking about. Deal? 



HFroller said:


> A very good text, Goldstein, but a bit old-fashioned.


The paper I was referring to was from the 80s as well.



HFroller said:


> I could add Quantenmechanik und Gruppentheorie by Weyl. Not relevant here, just to show that I recognize nice mathematical machinery when I see it.


That's nice, but as you say irrelevant here.



HFroller said:


> Or would you like to know more about index theorems for partial differential equations? If you don't know anything about index theorems for PDE's, I rather doubt that you could tell me - or anybody else - something interesting about mathematical machinery.


A good part of my work is in theoretical fluid mechanics, most of it focusing on the mathematics of the Navier-Stokes equations, with some connections to the existence and smoothness problem for their solutions. Trouble is, the theory of elliptic operators is an insufficient framework to understand these. I do still have an adjoint position in Applied Mathematics. Yes, I do know just a thing or two about PDEs. 

So, with introductions out of the way, and given that you do seem to have the background to understand what I was saying, do you have any other remarks on the topic beyond general amusement? Perhaps a position on topic, even? :wink:


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## nhluhr (Sep 9, 2010)

ibericb said:


> Air apparent? What does that mean?


It's a misuse of the correct phrase "heir apparent". He might as well have said "could care less" or "for all intensive purposes"


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## cxwrench (Nov 9, 2004)

davidka said:


> That was the late 90's. They realized that lateral flex was a key component for cornering traction. They also use a smaller diameter rear wheel (making up the diameter with a taller tire) for the same reason.


I'm guessing you're replying to my post about MotoGP, but there's no way to really know. Try the 'quote' button.


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## HFroller (Aug 10, 2014)

Pirx said:


> Well, if you know mechanics then this might seem trivial, but it's clearly a concept that's not generally understood, at all. At least the layman very often does not recognize nor understand the farther-reaching consequences of energy conservation principles. Amusing?
> 
> (...)
> 
> ...


No pissing contest intended. You asked for my credentials, I gave them.

I would like to submit a positive contribution to this discussion, but a) the combination of bike + rider is a highly complex system, and b) honestly, the discussion didn't have a positive start to begin with. 

As you mention, energy conservation is not generally understood. And if you mix it with the work done by the rider - like lay people probably do - it becomes even more complicated. So why all the references to energy conservation? It doesn't clarify things. And no, energy conservation by the frame _in itself_ doesnt tell you anything about the efficiency of stiffer and less stiff frames. Imagine a perfectly elastic bottom bracket with an eigenfrequency equal to a typical pedaling frequency - how would that work? (I don't know the answer, but I'm curious!) There are many factors that come into play. 

So yes, I found the references to energy conservation amusing. They create a feeling of understanding where there's actually no or very little understanding.


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## Pirx (Aug 9, 2009)

HFroller said:


> So why all the references to energy conservation? It doesn't clarify things.


Well, it doesn't clarify anything for you and I, but as trivial as this point is, it is often not understood. So, the point that _the flexible frame by itself_ does not lead to any losses whatsoever is important to drive home, as obvious as it may seem to you and I. To avoid any misunderstanding, it is understood that the idea of analyzing "the frame by itself" in this context makes little to no sense in the first place.



HFroller said:


> And no, energy conservation by the frame _in itself_ doesnt tell you anything about the efficiency of stiffer and less stiff frames.


Absolutely, I agree, and that was an important point I was trying to make.

The point is, then, that in order to be able to assess the relative efficiency of frames of different stiffness, one would have to model the entire system rider+bicycle. A crucial component in this respect then becomes the biomechanics of pedaling (the subject of the paper that I had linked to). It is clear that any benefits (or not) of stiffer frames must be sought in the way they may alter exactly that part of the system. This is an extremely complex topic, involving questions such as what happens to the components of the pedal stroke where certain muscle groups are forced into "negative muscle work" (situations where the muscle extends in the direction of an external force, which has a physiological cost, but represents energy _gain_ from the point of view of pure mechanics). To the best of my knowledge, there is no published work on that topic, so the bottom line is, _nobody knows what the effects of small changes of frame stiffness with respect to the efficiency of the bicycle-rider system are_.

This is where I started this thread, and this is the main point.


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## ibericb (Oct 28, 2014)

Pirx said:


> ... involving questions such as what happens to the components of the pedal stroke where certain muscle groups are forced into "negative muscle work" (situations where the muscle extends in the direction of an external force, which has a physiological cost, but represents energy _gain_ from the point of view of pure mechanics).


I'm havng trouble following your description. Are you referring to eccentric contractions during pedaling?


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## HFroller (Aug 10, 2014)

Pirx said:


> So the bottom line is, _nobody knows what the effects of small changes of frame stiffness with respect to the efficiency of the bicycle-rider system are_.
> 
> This is where I started this thread, and this is the main point.


It's an interesting and very valid point to make, now that every advertisement for & review of a new bike starts with a statement about the stiffness of the bottom bracket. Personally I thought you could have made it less aggressively when you started this thread. But that's just me.


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## aclinjury (Sep 12, 2011)

cxwrench said:


> I'm guessing you're replying to my post about MotoGP, but there's no way to really know. Try the 'quote' button.


i'm not sure what you and davidka were referring to in regard to Honda, but Ducati a few seasons ago tried a carbon swingarm on their GP bike (this was when Stoner and Hayden were on the Ducati team). The result was that the swingarm was simply too stiff and did not provide enough traction nor lateral flex. So while in theory, carbon fiber can be tuned infinitely, in practice it is MUCH harder to find this magical tune in carbon fiber eh. In the end, it was an expensive engineering lesson for Ducati. They ditched it at half season.


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## duriel (Oct 10, 2013)

So.. stiffer frames are faster, right!


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## Pirx (Aug 9, 2009)

ibericb said:


> I'm havng trouble following your description. Are you referring to eccentric contractions during pedaling?


Not sure if that's the same thing as "eccentric contractions", but the basics of what I am talking about are as follows: Imagine doing barbell curls with a heavy weight; clearly, when you lift the weight you have your biceps contracting when pulling the weight up, so your muscles are doing work that ends up in potential energy of the weight (you have lifted up the weight against gravitation). So, your muscle cells burn energy that ends up in increased potential energy of the weights, so no problem. Well, not all of the energy of the fuel gets converted, since efficiency is less than 100% of course, but you get the idea. 

Now imagine lowering the weight: In this case your muscles exert a force in the same direction as before, this time, however, extending. From the point of view of mechanical energy, the potential energy of the weight decreases, and it could be converted, in principle, into some other form of energy, such as some form of potential energy stored in your muscles. Indeed, if those muscles were perfect elastic springs, then that is what would happen. However, it turns out that not only is no energy returned to the muscles (*), but your muscle cells in fact still metabolize fuel, i.e., they burn energy. Thus the net effect here is that not only do you not get the energy back that you invested when you lifted the barbell, but you actually have to waste additional energy to lower the barbell back down. Clearly this is a wildly inefficient process.

Now, if you analyze the pedaling motion of a cyclist, where a whole set of muscles participate in producing the power to turn the pedals, it turns out that during various phases of the pedal stroke various muscles are in the same situation as we saw in the barbell example above, and are thus wasting energy. The details are complex, but the  article I mentioned earlier contains quite a bit of information on those. As a consequence, it is crucial to understand the detailed kinematics and dynamics of the pedaling motion if one wants to analyze its efficiency, which is exactly what the author of the above article suggests. Naïve notions of the "phase to help with the opposite leg applied power" are pretty much useless in such an investigation.

(*) I am by no means an expert, but I think I read somewhere that our muscle cells are in fact to some degree capable of the feat of converting some of this energy back into some usable form, at least for dynamic (rather than quasi-static) cases. This means the picture isn't quite as bleak as what I described above. Thus motions like running of many land animals are more efficient than one might expect. And clearly, different animals have developed different strategies to optimize these motions via different types of gaits, presumably in an effort to optimize the energetics of the motion.


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## jfaas (Jan 31, 2014)

I like turtles.



Also, my steel lemond is plenty stiff for out of the saddle efforts.


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## aclinjury (Sep 12, 2011)

HFroller said:


> It's an interesting and very valid point to make, now that every advertisement for & review of a new bike starts with a statement about the stiffness of the bottom bracket. Personally I thought you could have made it less aggressively when you started this thread. But that's just me.


That's how Pirx is. That is his style. What I like about him is he spends time to point out the technicals when need be, and it's up to the other person to find out further. He can sound harsh at time, he doesn't baby people. He's sort of like an impatient college professor telling the students what they need to know. Personally I'm fine with that. Doesn't hurt my feeling at all. I rather have that than some Joe who doesn't understand much but likes to flash marketing literatures as proof of anything.


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## Pirx (Aug 9, 2009)

duriel said:


> So.. stiffer frames are faster, right!


The answer is (wait for it...): Nobody knows, but most likely the effect is near-zero, and certainly much less than the effect of fitting parameters, such as saddle height.


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## robt57 (Jul 23, 2011)

aclinjury said:


> That's how Pirx is. That is his style. What I like about him is he spends time to point out the technicals when need be, and it's up to the other person to find out further. He can sound harsh at time, he doesn't baby people. He's sort of like an impatient college professor telling the students what they need to know. Personally I'm fine with that. Doesn't hurt my feeling at all. I rather have that than some Joe who doesn't understand much but likes to flash marketing literatures as proof of anything.


He is a sanctimonious lot, not meant pejoratively.  Well, maybe just a little.
I was happy to see in subsequent postings as the thread progressed, a more intellectual layer appeared. Else I would not be lurking still. He is the kind of fellow I would give notice to quickly if I worked for him I'd say observationally [made up word, I know]. If asked why I gave notice, I would say to avoid telling you to go fly a kite. Well, probably not that soft in actual verb-age...


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## Pirx (Aug 9, 2009)

aclinjury said:


> That's how Pirx is. That is his style.


Yep. I was going to say: It's a matter of style, and adapting style to the audience. In this forum, if I say something like "I would like to begin a dialogue on the subject of frame stiffness, and stimulate a more critical attitude towards the popular idea that increased frame stiffness always leads to increased efficiency", all I would probably get is blank stares, and some yawns. On the other hand, if I say "Anyone who seriously believes that stiffer frames are better is a ****ing moron", then people wake up and pay attention.

On the other hand, when I submit a journal paper, I'm usually taking the first approach. More or less... 



robt57 said:


> He is a sanctimonious lot, not meant pejoratively.  Well, maybe just a little...


You mean "sanctimonious lout"?


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## ibericb (Oct 28, 2014)

robt57 said:


> He is a sanctimonious lot, not meant pejoratively.  Well, maybe just a little.
> I was happy to see in subsequent postings as the thread progressed, a more intellectual layer appeared. Else I would not be lurking still. He is the kind of fellow I would give notice to quickly if I worked for him I'd say observationally [made up word, I know]. If asked why I gave notice, I would say to avoid telling you to go fly a kite. Well, probably not that soft in actual verb-age...


Pirx comes off here pretty much like any one of the 24 PhD's I had working for me in my one of my groups, but at about a10-fold dilution,. At that time I was probably pretty much the same. You should try working and living in a demanding, high-power, technical research culture for a few years. If you find his online demeanor here offensive, the you're probably right - you wouldn't last very long in a real work environment of that type.


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## Pirx (Aug 9, 2009)

Oh, and there's one more element to the picture here, pertaining to this meme of my "arrogance". Here's the deal: Most people not working in the sciences do not realize that the "hard" sciences (physics, chemistry, math) are very, very _deep_. 

What I mean by this is that, in order to even begin to understand any non-trivial question in any of these fields, you have to put in some serious work. This is because many important results are ultimately built on many, many layers of other results, and cannot be understood without also understanding the underlying facts and theories. 

Thus, if people feel that I am uncooperative in explaining certain things to them, then that's not because of me being obstinate, or arrogant, but simply because, in order to understand certain topics you have to put in the work, and study the pertinent mathematics, or physics, etc., not for five minutes, not for an hour or two, but for weeks, or months, or even years in some cases. Some things you can't just google and digest within the typical attention span of the Twitter generation. For some of the topics we are discussing here, if you are not familiar with the pertinent science, your only options really are to either (a) trust me, or (b) buckle down and study the literature. There's no easy shortcuts, sorry.


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## ibericb (Oct 28, 2014)

Pirx said:


> Not sure if that's the same thing as "eccentric contractions", but the basics of what I am talking about are as follows: ...
> 
> Now* imagine lowering the weight: In this case your muscles exert a force in the same direction as before, this time, however, extending*.


That's the classic example of eccentric contraction. It is basically muscle fiber contraction as the muscle is lengthening rather than shortening (which is concentric contraction). Eccentric contractions are typical when motion is being slowed against an external force. The lowering of the weight from a biceps curl is one, the descent on a squat is another, a gymnast landing a vault, a landing off a box jump. Those muscle contractions provide the arresting force necessary to control movement against what otherwise would be overwhelming external forces, usually due to gravity. One of the downsides to eccentric contractions is they can be very damaging to muscle fibers and tissue.

As for the relevance in cycling and pedaling, I can only see it being pertinent in fixed gear for slowing and stopping. In more conventional freehub or free wheel systems it might be relevant in overcoming inertia in stopping leg motion. But in simple thought I can't see it being relevant in developing force for propulsion.

The organization of cells and proteins in muscle fibers does a good job of converting chemical energy into mechanical energy. But, as best I know, they don't effect the opposite. You can't drive ATP production from muscle fiber extension.


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## ibericb (Oct 28, 2014)

Pirx said:


> Oh, and there's one more element to the picture here, ...


As any fool can plainly see.


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## Pirx (Aug 9, 2009)

ibericb said:


> As for the relevance in cycling and pedaling, I can only see it being pertinent in fixed gear for slowing and stopping.


See the article I linked to. I thought the same thing you did, but apparently, if you look at all of the major muscle groups involved, eccentric contractions occur for quite a few of them during various phases of the cycle.



ibericb said:


> You can't drive ATP production from muscle fiber extension.


Like I said, I just dimly remember reading something about this, and I really don't remember at all what the exact mechanism for energy recovery was. I'm pretty sure it was not a biochemical process (such as converting work into ATP), but some sort of some micro-biomechanical effect; perhaps some elasticity of the muscle cells or something of that sort. I don't really know what I am talking about here, because I honestly don't remember the details. I just distinctly remember seeing something about how not all of that energy is lost, somehow.


----------



## tvad (Aug 31, 2003)

Pirx said:


> Oh, and there's one more element to the picture here, pertaining to this meme of my "arrogance". Here's the deal: Most people not working in the sciences do not realize that the "hard" sciences (physics, chemistry, math) are very, very _deep_.


Oh please, what utter BS. You cannot see the forest from the trees when it comes to the breadth of your arrogance...and it has _absolutely nothing to do with us not understanding the science_. It has _everything_ to do with your attitude, presentation, and the complete lack of tact or social skills displayed in post after post in this thread.

Damn, Prix, get a clue already.


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## Mandeville (Oct 18, 2014)

When I was young man I was on different occasions exposed to the presence of Edward Teller, the "father" of the H-Bomb. Prix online persona usually reminds me of Teller's persona. Teller's persona or "style" was such that everyone that I know of that was exposed to teller were unanimous in their shared same opinion of that persona.


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## Pirx (Aug 9, 2009)

tvad said:


> Damn, *Pirx*, get a clue already.


FIFY

And: :ciappa:


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## ibericb (Oct 28, 2014)

Without getting rigorous, I think I basically understand Papadopoulos's model, and his assessment. It appears to me that the basic problem in comparison to real systems is the generalization that an ineffective actuator in his kinematic model will absorb work bears a resemblance to relaxing contraction in a real muscles. 

Muscles don't absorb work in the sense he is using it in his kinematic model. A lengthening fiber isn't "absorbing work" as it is described for one of his actuators. It may be still contracting as it lengthens, as in the previously noted eccentric contraction, in which case those fibers of the muscle unit are doing a lot of work to arrest an extending motion. Or the fibers may be relaxing without contractile opposition as part of a recovery phase, in which case an opposing muscle group is doing work to extend the limb about the joint in the opposite direction, now unopposed by the previous groups ceased contractions. In this latter case the elongating fibers are, in a sense, being "worked on" as the fibers are being extended via opposing muscle group work.

While I think the description is a bit loose, the impact on overall efficiency, which I believe was his point and reason for exploring the model as representative, is valid. To that point, eccentric contractions that might occur during propulsive pedaling efforts would work in opposition to the supposed intent, and thereby decrease efficiency.


----------



## Pirx (Aug 9, 2009)

jfaas said:


> I like turtles.


I like bunnies. This one is for my friend tvad, very tactful, to showcase my massive amount of social skills:


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## tvad (Aug 31, 2003)

Pirx said:


> FIFY
> 
> And: :ciappa:


Thanks. Darned auto correct.

:ciappa: would likely be more pleasant than reading many of your posts herein.


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## aclinjury (Sep 12, 2011)

Pirx said:


> The answer is (wait for it...): Nobody knows, but most likely the effect is near-zero, and certainly much less than the effect of fitting parameters, such as saddle height.


I'd guess sitting on the saddle and motoring is more efficient than standing and mashing. And if you're the stand and mash type, perhpas stiffer may be more efficient. But then again, for the majority of the people, cycling should be sitting and spinning


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## myhui (Aug 11, 2012)

Pirx said:


> I like bunnies.


Yup.










That is one fierce looking cottontail rabbit!


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## HFroller (Aug 10, 2014)

Mandeville said:


> When I was young man I was on different occasions exposed to the presence of Edward Teller, the "father" of the H-Bomb. Prix online persona usually reminds me of Teller's persona. Teller's persona or "style" was such that everyone that I know of that was exposed to teller were unanimous in their shared same opinion of that persona.


Comparing someone's personality with Teller ... now there's an insult. 
I retract my remark Pirx, everything is forgiven!


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## Pirx (Aug 9, 2009)

tvad said:


> :ciappa: would likely be more pleasant than reading many of your posts herein.


Heh, to each his own, I guess... 




HFroller said:


> Comparing someone's personality with Teller ... now there's an insult.
> I retract my remark Pirx, everything is forgiven!


Yeah, I was taken aback a little myself...


----------



## ibericb (Oct 28, 2014)

Okay, the concept got me curious enough to go back and revisit some fundamentals of muscle action. In that course I came upon this article,which directly addresses the topic. The explanations offered are making clear my appreciation of the total of muscular-skeletal movement, it's origins, the mechanics and energy flows have been limited. This is indeed quite interesting. However, I'm still wrestling with the structural basis for elastic energy storage in muscular-skeletal systems that aren't contractile in origin. The energetic studies appear to indicate rather clearly that something is going on. But the appreciation of exactly what hasn't sunk in yet.

edit added - another, more recent article that sheds light on the structural elements involved, and confirms the energetic impact.


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## Fireform (Dec 15, 2005)

Pirx said:


> Oh, and there's one more element to the picture here, pertaining to this meme of my "arrogance". Here's the deal: Most people not working in the sciences do not realize that the "hard" sciences (physics, chemistry, math) are very, very _deep_.
> 
> What I mean by this is that, in order to even begin to understand any non-trivial question in any of these fields, you have to put in some serious work. This is because many important results are ultimately built on many, many layers of other results, and cannot be understood without also understanding the underlying facts and theories.
> 
> Thus, if people feel that I am uncooperative in explaining certain things to them, then that's not because of me being obstinate, or arrogant, but simply because, in order to understand certain topics you have to put in the work, and study the pertinent mathematics, or physics, etc., not for five minutes, not for an hour or two, but for weeks, or months, or even years in some cases. Some things you can't just google and digest within the typical attention span of the Twitter generation. For some of the topics we are discussing here, if you are not familiar with the pertinent science, your only options really are to either (a) trust me, or (b) buckle down and study the literature. There's no easy shortcuts, sorry.


Oh please. I've held my tongue up until now but this is really too much. As I'm sure you're aware, there's a saying in science that if you can't explain it simply you don't understand it well enough. 

You aren't the only person in this forum with a PhD in hard sciences. Massive condescension is not an effective tool for explaining anything, and you have thus far explained very little except to make clear that you're an arrogant ****.


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## aclinjury (Sep 12, 2011)

Fireform said:


> Oh please. I've held my tongue up until now but this is really too much. As I'm sure you're aware, there's a saying in science that if you can't explain it simply you don't understand it well enough.
> 
> You aren't the only person in this forum with a PhD in hard sciences. Massive condescension is not an effective tool for explaining anything, and you have thus far explained very little except to make clear that you're an arrogant ****.


just when I thought everyone was making up and chilling down, of course you have to repeat something already said. Ya late to the party. God, I hope Pirx can restrain from replying to your post as it'll only just another pissing contest.


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## jfaas (Jan 31, 2014)

myhui said:


> Yup.
> 
> 
> 
> ...


I'd be mad too if someone threw snow in my face!


----------



## myhui (Aug 11, 2012)

jfaas said:


> I'd be mad too if someone threw snow in my face!


Buns have feelings too.


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## Pirx (Aug 9, 2009)

aclinjury said:


> God, I hope Pirx can restrain from replying to your post


Nah, not interested. Like you said, we're making some progress towards bringing this back to a more rational level, so why add to the noise?

I have some additional thoughts on the topic which may be helpful, but I don't have time for this right now; perhaps tonight.


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## robt57 (Jul 23, 2011)

nhluhr said:


> It's a misuse of the correct phrase "heir apparent". He might as well have said "could care less" or "for all intensive purposes"



All slang is mis-use technically.


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## duriel (Oct 10, 2013)

Wasn't there a tree around here somewhere?????


----------



## berserk87 (Jul 24, 2014)

goodboyr said:


> OK. Understood and thanks for the clarification.
> 
> This thread is crying for moderator involvement. That's not crying to "mommy". People clearly don't realize how insulting they are, and how it turns others off from participating and learning. So, in that particular case, I respectfully disagree.


Yeah - I think that there may be some good info in this thread but I got tired of having to filter through all of the petty egos and insults and skipped a bunch of it. This was the first post I read after a long hiatus from the forum. Now I remember why I don't come here more often.


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## Pirx (Aug 9, 2009)

HFroller said:


> As you mention, energy conservation is not generally understood. And if you mix it with the work done by the rider - like lay people probably do - it becomes even more complicated. So why all the references to energy conservation? It doesn't clarify things. And no, energy conservation by the frame _in itself_ doesnt tell you anything about the efficiency of stiffer and less stiff frames. Imagine a perfectly elastic bottom bracket with an eigenfrequency equal to a typical pedaling frequency - how would that work? (I don't know the answer, but I'm curious!) There are many factors that come into play.


Your paragraph above got me thinking, and I feel it might be worthwhile to explicitly discuss another trivial consequence of energy conservation for the case of the elastically deforming frame (no material damping). 

I think by now pretty much everyone agrees that such a frame will not "absorb" any energy, but the valid point is brought up that perhaps energy is lost in the interaction of the rider with such a frame. People then tend to launch into speculation as to how the timing of the "unwinding" of the frame relative to the pedal stroke may be important (such as the argument presented by stevesbike involving the "phase to help with the opposite leg applied power"). Such ideas are largely misguided, but their rhetorical advantage is that they force you into a consideration of the detailed kinematics and dynamics within the system which nobody has studied in sufficient detail. In order to cut through some of the fog generated by this approach, the following thought experiment might be helpful:

Let us consider a system consisting of our ideal, elastically deforming frame, this time, however, powered by a perfect motor (100% efficiency). If you like you can imagine a system with various pushrods modeling the foot, lower and upper legs of a cyclist, connected via frictionless joints, and powered by an ideal electrical motor driving some sort of an appropriate crank. You may even imagine those elements having masses and mass distributions that model the actual legs of a cyclist. 

Now, it is trivial to see that in this system, frame stiffness once again has no effect: The output power appearing at the rear wheel of such a system will be _exactly the same_ regardless of the stiffness of the frame (see below for two caveats). Like I said, this may seem like a trivial statement, but it illustrates an important point: _If there are differences in efficiencies between frames of different stiffness, then their source must be sought in the specific bio-mechanics of the rider_. Thus this question is never a simple question of the kinematics and dynamics of a rigid mechanical system. In my model above, those phases that people are talking about will automatically adjust in such a way that no energy is being lost, and I can know this without ever bothering to look into those details, which might be quite complex even in my model system.

So, at this point what we are saying is that, it is not impossible that the small motion of the frame under deformation (note that typical deformation amplitudes at the pedals are of the order of less than a half inch, in extreme cases) of the flexible frame makes the motion of the rider less efficient, but the opposite may be true just as well. Ultimately, which one is the case would have to be explored experimentally, but as a cautionary tale one may consider the case of studies were people explored the effect of crank length on cycling efficiency. I can't find the specific study I have in mind right now, but I remember one where crank lengths in the extreme range between 140 and 200mm or so were tested, and it appeared that there were little to no significant differences in efficiency or muscle fatigue (two different issues, by the way). Also, it is plausible that whether additional frame stiffness has positive or negative effects may well depend on the specific rider and the specific fit of that rider on a given bicycle.

Bottom line: _There is, at present, no reason to assume that stiffer frames are more efficient_.

Two caveats with the above model: First, we are only following power output up to the rear wheel. It is possible that deformation of the rear triangle as well as the front of the bike may change tracking in a way that has energetic consequences. However, we may notice that the minute details of exactly how a bicycle ridden by a real cyclist tracks, under various scenarios (sprinting, hill climbing, cruising) are quite complex also, so again, whether or not increased frame flex is good or bad is unknown.

Finally, on your remark regarding pedaling frequency matching the eigenfrequency of the system, well, the answer to this is obvious, at least in the linear approximation that generated the eigenvalue problem: The amplitude of the eigensolution is indeterminate of course, and practically speaking you would see exponentially increasing amplitudes of the frame deflection. Energetically this means that indeed more and more energy is being pumped into the frame oscillation, so energy would indeed be "lost" to propulsion. However, this system has no steady state, and the linear approximation would break down very quickly anyway. Thankfully, given that typical frame eigenfrequencies of realistic bicycle frames are far higher than the pedaling cadence, we don't have to worry about this scenario.


----------



## Z'mer (Oct 28, 2013)

Pirx said:


> I think by now pretty much everyone agrees that such a frame will not "absorb" any energy, but the valid point is brought up that perhaps energy is lost in the interaction of the rider with such a frame. People then tend to launch into speculation as to how the timing of the "unwinding" of the frame relative to the pedal stroke may be important (such as the argument presented by stevesbike involving the "phase to help with the opposite leg applied power")...
> 
> Such ideas are largely misguided, but their rhetorical advantage is that they force you into a consideration of the detailed kinematics and dynamics within the system which nobody has studied in sufficient detail...
> 
> ...


Can you please identify or further explain how you have used the "scientific method" to arrive at the conclusions above? 
I am looking for original thought from you on this. Identification of 3 or 4 typical rider scenarios, then identification of typical driving forces. Definition of input forces, drawn from vector equations of motion (in all dimensions referenced to a defined point) with simplifying assumptions and reasons why, then simplify it to reason out major driving forces under 3 or 4 rider loads. Then the frame response, again, defining all possible frame response forces, then simplifying with reasons why. With discussion of the above static analysis to draw conclusions over say, 12 crank angle positions and how this would translate to torque and power output at the rear wheel. 

This is how I was schooled to solve a problem like this, given defined input conditions, when I studied mechanics of materials, statics and dynamics. Perhaps this no longer holds? Now do people simply tell everyone they are too dumb to understand, and get away with it?


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## Pirx (Aug 9, 2009)

Z'mer said:


> This is how I was schooled to solve a problem like this, given defined input conditions, when I studied mechanics of materials, statics and dynamics.


You education in mechanics was limited, it seems. As I have explained multiple times in this thread, there are other approaches that allow me to make definite statements like the ones I have. Exploiting ideas of energy conservation is the prime one used in this thread. Feel free to ask if you see any mistakes or flaws with the arguments I have presented.



Z'mer said:


> Perhaps this no longer holds?


It has not held for over 150 years now. It is now well understood that Hamiltonion or Lagrangian frameworks have significant advantages over the simple vector mechanics you are referring to. These are in fact based on general variational principles closely related to the energy conservation ideas I have been emphasizing.



Z'mer said:


> Now do people simply tell everyone they are too dumb to understand, and get away with it?


There is a difference between lacking knowledge in a specific field and being dumb. There is no shame in not being an expert in theoretical mechanics, say. Consequently you will find that I have never called anybody dumb in this thread. However, in my book claiming understanding of a non-trivial question in a field outside of one's competence is indeed a form of arrogance. Think about it.

P.S.: Trying to snow an expert in any given field with jargon from that very field is a bad idea. :wink:


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## ibericb (Oct 28, 2014)

The more I thought about this issue over the past week, the more I am inclined to agree with your assessment. In that time I've tired, using a limited classical approach, to more completely resolve the force dynamics, and the attendant impact on work and energy. Considering a complete pedaling cycle, and continuing cycles, I find that what I lazily thought (absent thoughtful analysis) were departures from the idealized system in fact integrate into the same net conservation. It seems to me the more broadly you define and look at the system as a whole, the more clearly the question of frame stiffness becomes irrelevant.

The departures from that broad conclusion seem to me to be limited to, (1) losses due to material hysteresis effects (which in modern frame materials within their elastic limits is negligible), and (2) losses to moving the rider around (i.e., spring work done on the cyclist position, etc.). I tend to thing the latter may be one of the keys to differences in preference between different cyclist, and dynamically may have some effect on the efficiency of force to power conversion for any particular cyclist.

While I agree with you broadly about energy, I am still in a bit of a quandary about power produced due to the instantaneous element of power, which leads into the whole dynamics question. While the simple case of average power over a cycle revolution at a fixed cadence should be constant for the same total energy, it seems to me that instantaneous power at any point in the cycle can be different. What's not clear to me is how the subtle changes in instantaneous power coupled with a constraint of equivalent average power may affect net bicycle performance.


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## aclinjury (Sep 12, 2011)

I got a question for you guys. So assuming that hysteresis loss is negligible, drivetrain loss negligible, then is it correct to generalize that the power you put in either moves you forward or up&down (bobbling, as in mountain bike)? So here's my question, if the frame is flexible vertically (eg, a mountain bike with suspension), then the power also goes into driving you up and down as opposed to forward, right?


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## HFroller (Aug 10, 2014)

aclinjury said:


> I got a question for you guys. So assuming that hysteresis loss is negligible, drivetrain loss negligible, then is it correct to generalize that the power you put in either moves you forward or up&down (bobbling, as in mountain bike)? So here's my question, if the frame is flexible vertically (eg, a mountain bike with suspension), then the power also goes into driving you up and down as opposed to forward, right?


The big difference between an MTB and a race bike is that the suspension of the MTB is designed to absorb energy. The starting point of this thread was that a race frame _does not _absorb energy. I believe this to be correct to high degree of accuracy. Intuitively I also believe that keeping a sideways oscillating movement of the bottom bracket going will cost you energy you can't use for propulsion - even if the frame does not absorb this energy. 

What's totally unclear to me is if a stiffer frame makes a difference in this respect. Does a sideways oscillating movement cost you less energy when the frame is stiffer? I don't know.

I think Pirx nailed it when he wrote that we have to know more about the biomechanics of the rider to answer that question.


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## ibericb (Oct 28, 2014)

aclinjury said:


> I got a question for you guys. So assuming that hysteresis loss is negligible, drivetrain loss negligible, then is it correct to generalize that the power you put in either moves you forward or up&down (bobbling, as in mountain bike)?


The power you develop through application of force to the pedals goes into overcoming a number of opposing forces. At typical road riding situations most notable among those is aerodynamic drag, and changes in kinetic energy. Then there's rolling resistance, drivetrain efficiency, and various frictional losses (bearings and the like). The point is all of those seek to consume energy and power, and all of those are greater than anything you may loose in efficiency to frame flexibility.



> So here's my question, if the frame is flexible vertically (eg, a mountain bike with suspension), then the power also goes into driving you up and down as opposed to forward, right?


Setting aside shock absorption and suspension issues, let's start with a very simple consideration of applying force to pedals while seated to propel the bike forward. First, you sit on the bike with feet on the pedals, same load on both pedals, going nowhere. Based on your weight distribution between upper body contact (bars) and lower body contacts (saddle and pedals) a force is applied to the frame, and some flex occurs. The force applied is a result of the riders mass and the force of gravity, so no rider effort to propel the bike is lost in that initial loading.

From that static position when you apply a differential force to the pedals you unload one pedal and load the other. You do metabolic work to change that loading. At the same time you seek to apply a force to one pedal and remove the load from the other the equal and opposite reaction from the pedal where the load is increased tries to force the cyclist away. That is overcome by a weight shift, either from static supported weight on the saddle to the leg and foot support, or from weight supported on the opposite foot being unloaded. However, the load on the frame remains the unchanged. So your applying force on a pedal doesn't alter the vertical load on the frame or the frame's displacement from unloaded. That's seated.

When you move to stand you shift more of the weight (force) from saddle support to the feet and pedal support. Still the load on the frame remains the same. However, in getting into that position you had to allow some of your applied effort go into raising your body position, so that amount of work you did is not captured in developing force to pedal - you moved yourself for a position advantage. But that work did not go into flexing the frame.

In this simple consideration the only times I can see vertical frame flex from rider effort altering the loaded vertical frame flex is when the load is shifted by fore-aft weight distribution, or when muscular effort is used to develop more force than weight shift alone allows by pulling on the bars to force the lower body down, increasing the load though the legs and on the pedals. 


That's my simplistic view, which basically suggests that vertical frame stiffness is not an issue in force to power conversion efficiency. I trust Pirx will come along and correct any number of errors in this overly simple and narrow description.

I believe the greater issue with vertical stiffness and performance are the adverse effects of suspension losses to kinetic energy loss, and cyclist comfort allowing him to stay in a desired position and develop power.


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## duriel (Oct 10, 2013)

Stiff frames are always faster. If you push and the power is not transfered to the wheel, it is lost.


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## Pirx (Aug 9, 2009)

ibericb said:


> That's my simplistic view, which basically suggests that vertical frame stiffness is not an issue in force to power conversion efficiency. I trust Pirx will come along and correct any number of errors in this overly simple and narrow description.


Nah, he won't. 



ibericb said:


> I believe the greater issue with vertical stiffness and performance are the adverse effects of suspension losses to kinetic energy loss, and cyclist comfort allowing him to stay in a desired position and develop power.


I agree.



duriel said:


> Stiff frames are always faster. If you push and the power is not transfered to the wheel, it is lost.


Heheh, very funny. You're quite the joker, are you not?


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## ibericb (Oct 28, 2014)

duriel said:


> Stiff frames are always faster.


Is "stiff" an absolute? Is a frame either stiff or flexible?



> If you push and the power is not transfered to the wheel, it is lost.


When and how does that occur?


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## ibericb (Oct 28, 2014)

Pirx said:


> Nah, he won't.


But, but ... 

Get laid last night?


----------



## Pirx (Aug 9, 2009)

ibericb said:


> But, but ...
> 
> Get laid last night?


You, my friend, are surprising me now.


----------



## ibericb (Oct 28, 2014)

Pirx said:


> You, my friend, are surprising me now.


Sorry - after bending my old, feeble brain so early in the morning I just couldn't resist the opportunity.


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## nhluhr (Sep 9, 2010)

robt57 said:


> All slang is mis-use technically.


"heir apparent" is not slang. It's a specific term referring to succession or passing of property.


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## PBL450 (Apr 12, 2014)

ibericb said:


> Pirx comes off here pretty much like any one of the 24 PhD's I had working for me in my one of my groups, but at about a10-fold dilution,. At that time I was probably pretty much the same. You should try working and living in a demanding, high-power, technical research culture for a few years. If you find his online demeanor here offensive, the you're probably right - you wouldn't last very long in a real work environment of that type.


I wouldn't restrict that to hard sciences. It's no different in a publish or perish environment in more stats oriented sciences in my experience of doing this for a long time. Lots of sleepy BS mid size colleges and universities out there in terms of worthless BS PhD "haven't done any research since my dissertation" faculty, but in the R1s, again, in my experience, you get the elite scholar. Giant egos bouncing around smashing into each other... They are experts. It is part of the DNA that makes them experts. Myopic? You bet. Experts in very highly defined areas most people could give two sh*ts about, at least on the level they understand their unique scholarly niche. As it should be. We need the stem cell research institute at Rutgers and we need the steel research lab at Pitt. It just takes a certain person to want to do that. Like it takes a certain person to be a cancer nurse. Or a social worker or an elite cyclist. All of whom are putting in the work, believe me.


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## GlobalGuy (Jun 9, 2015)

Despite the OP title and there is data and opinion related to the title it quite clear from reading the thread that frame stiffness was never the primary subject or focus of the OP.


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## Pirx (Aug 9, 2009)

GlobalGuy said:


> Despite the OP title and there is data and opinion related to the title it quite clear from reading the thread that frame stiffness was never the primary subject or focus of the OP.


That would be news to the OP. It is indeed clear, however, that it is not the focus of your contribution to this thread.


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## aclinjury (Sep 12, 2011)

Pirx,
this is a bit of a late reply, but you said in a post somewhere way back that math is a hard science. Hmmm, math is a language, and many universities will put math under the school of philosophy or the humanities. Just a sidenote at this point! ;-)


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## Pirx (Aug 9, 2009)

aclinjury said:


> Pirx,
> this is a bit of a late reply, but you said in a post somewhere way back that math is a hard science. Hmmm, math is a language, and many universities will put math under the school of philosophy or the humanities. Just a sidenote at this point! ;-)


This is a valid point. Yes, in the strictest sense mathematics is not a science, since its subject is really outside of physical reality. Going any further on this would take us very far outside of the topic of this thread, however, so let's just leave it at that.


----------



## Z'mer (Oct 28, 2013)

Pirx said:


> You education in mechanics was limited, it seems. As I have explained multiple times in this thread, there are other approaches that allow me to make definite statements like the ones I have. Exploiting ideas of energy conservation is the prime one used in this thread. Feel free to ask if you see any mistakes or flaws with the arguments I have presented.
> 
> ...It has not held for over 150 years now. It is now well understood that Hamiltonion or Lagrangian frameworks have significant advantages over the simple vector mechanics you are referring to. These are in fact based on general variational principles closely related to the energy conservation ideas I have been emphasizing.
> 
> P.S.: Trying to snow an expert in any given field with jargon from that very field is a bad idea. :wink:


Hey man
I wanted to reply to this, but wanted to go back and read all the linked stuff first, in case I missed something major in my thought process. 

The last paper I read, posted by ibericb was the Calspan one, which does a terrific job with the topic. This is the best paper, of all the links provided, to understand what is really going on, if you want the analysis

http://bicycle.tudelft.nl/schwab/Bicycle/calspan/CAL_ZN-5431-V-2.pdf

But you need to read it very carefully, and not cherry pick conclusions. 
and guess what - the entire section about energy stored and returned in the frame via the pedal / crank is based on 2 classical Newtonion equations and some undergraduate level calculus. Namely, the equations for torque, and linear spring force. Amazing! That analysis was done in 1974, and did not need to use "Hamiltonion or Lagrangian frameworks". 

So calling Newtonion equations 150 years obsolete or "whatever" for solving basis structural problems is a little over the top, maybe? 

Also not understanding your continuing statements (above) about "energy conservation ideas" which you have already admitted in previous posts means nothing more than linear springs are "conservative", i.e. they return all their work energy. 

As for snowing anyone with jargon, maybe a look in the mirror would help? This problem is maybe at best a good junior level ME homework problem to set up. The idea that one needs to be versed in math suitable for quantum mechanics to understand it is really, well, pushing the limit of your credibility that you understand it yourself.

The Calspan paper points out the special case (with boundary conditions) where pedal load is defined by a nice cosine function, and load = 0 at the pedal positions of 0 and 180 degrees from TDC. In this simple case the math works out nicely to show all pedaling energy used to flex the frame is returned.

But - they also consider cases where it does not, such as standing climbing, as shown in figure 6B and 6C on page 16. From the paper

"However, it is apparently possible for a force-deflection characteristic such as that shown in Figures 6b and 6c to occur in practice. These two figures reflect the same rider force input, Figure 6b showing force versus deflection and Figure 6c showing force versus crank angle. In this case, wasted rider energy could also approach a maximum of twice the energy stored in the spring when the full down position is reached. This factor of two arises from (1) the energy stored in the spring when the pedal reaches the full down position plus (2) the fact that spring unloading in crank positions past 180 degrees provides negative driving energy because it acts to reduce crank angle."

And we know our legs cannot absorb the negative energy, so it's wasted. 
What's interesting is that I had posted similar (not same) conclusions earlier in post #67 before reading the Calspan paper. I think you called this approach "misguided", but maybe I misunderstood the context. 

One last thing - if one is in the camp of agreeing with the BQ conclusions regarding frame stiffness, that would certainly conflict with statements along the lines of those made in post #1 by the OP - 
"Frame stiffness? Completely and utterly irrelevant." Right? 

I have no strong feelings one way or the other on frame stiffness, but like others here, would like to understand more about it. The BQ articles are interesting to me as I own mid 70's 531 frame bikes, bought new, along with modern Alu and carbon bikes.

So thanks for this thread, requesting maybe a little less spice next time, as others said, it gets in the way.


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## Pirx (Aug 9, 2009)

Z'mer said:


> So calling Newtonion equations 150 years obsolete or "whatever" for solving basis structural problems is a little over the top, maybe?


I never called them obsolete, and they are not obsolete. However, it turns out that they become very cumbersome in many cases. They still provide a complete description, mind you, but they're just hard to use, that's all.



Z'mer said:


> Also not understanding your continuing statements (above) about "energy conservation ideas" which you have already admitted in previous posts means nothing more than linear springs are "conservative", i.e. they return all their work energy.


The same can be true for nonlinear springs, of course.

And, no, my statements about energy conservation go much, much deeper than your trivial statement above. In fact, your not understanding that point of mine may be a main reason for your misunderstanding of my position, see below. I think you would benefit from making an effort to see this particular point; it's crucial.



Z'mer said:


> This problem is maybe at best a good junior level ME homework problem to set up.


That really depends on the approximations you are willing to make. If you want to include the mechanics of the rider, which I gather you seem to agree might be important (not entirely sure, feel free to correct me here) then it's definitely not a simple problem, see the paper from Ruina's group I had linked to.



Z'mer said:


> And we know our legs cannot absorb the negative energy, so it's wasted.


First, I wouldn't be so sure about what those legs (or, more precisely, the rider's body) can or cannot do. There was a bit of a discussion on the side on that topic (including kangaroos, and some remarks from ibericb); suffice it to say that that by itself is a non-trivial question. Second, what the author of the calspan paper did not consider at all, and the reason why their (weakly implied) conclusion is false, is that the kinds of motion they are talking about can, in principle, lead to exchange of potential energy for elastic energy when the riders vertical position is affected.

BUT, let me get back to my original point of using energy conservation to make my argument: _There is no need to speculate about those minutiae_. In the example of the "mechanical rider" I had discussed last, it is immediately clear that frame flexibility _cannot_ lead to a loss of energy. Note that this statement is rigorous under the assumptions made. Thus, I don't need to care about phases of this or angles of that; none of that matters, since I already know the outcome.



Z'mer said:


> So thanks for this thread, requesting maybe a little less spice next time, as others said, it gets in the way.


A matter of style, like I said. And other considerations, too.


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## Pirx (Aug 9, 2009)

As an aside, it just occurred to me how much this type of debate resembles the discussions that can be had with inventors of _perpetuum mobiles_ of the first or second kind. Believe me, I have seen my share of these guys and their contraptions... 

Just like in the discussion in this thread, the problem is that people come along with mechanisms or systems that may be enormously complex to analyze. There's cases I have seen where somebody would have to literally sit down for weeks to fully analyze the system in all of its details. I once had one of these guys walk into my office with a potential investor in tow, who offered me a lot of money to perform a computer simulation of his system. I (politely) declined. I did even more by explaining to these people that if they found somebody who was willing to take their money, they would be dealing with either a crook or an incompetent. 

Why did I do this? It's because we _know_ that the first and second laws of thermodynamics hold, and that means there is no such thing as a perpetual motion machine. It's the exact same knowledge that allows me to draw the conclusions about frame stiffness I have discussed here.


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## duriel (Oct 10, 2013)

I don't think you're getting it.

Energy is conserved, perfect. 

But, with a flexy frame it limits the available force to the wheel as the frame flexes, thereby not allowing the available force of the foot to apply power.


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## ibericb (Oct 28, 2014)

duriel said:


> I don't think you're getting it.
> 
> Energy is conserved, perfect.
> 
> But, with a flexy frame it limits the available force to the wheel as the frame flexes, thereby not allowing the available force of the foot to apply power.


I believe you're raising the one issue I haven't resolved in my own mind, and that is to what extent does instantaneous power at a point within a crank/pedal cycle determine performance vs. average power over a the same cycle?

edit added - FWIW, as best I can judge instantaneous force and power is only relevant for the corresponding instantaneous acceleration. In overall cycling performance it seems to me that the result integrated over a full cycle is more representative of net performance.


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## myhui (Aug 11, 2012)

ibericb said:


> I believe you're raising the one issue I haven't resolved in my own mind, and that is to what extent does instantaneous power at a point within a crank/pedal cycle determine performance vs. average power over a the same cycle?


Furthermore, to best take advantage of an oval chainring, a stiff frame does help.


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## Pirx (Aug 9, 2009)

duriel said:


> But, with a flexy frame it limits the available force to the wheel as the frame flexes, thereby not allowing the available force of the foot to apply power.


That's a neat example of how naïve intuition can go astray. "Available force" is not affected by frame flex. Frame flex or no, the force at the rear wheel is _exactly_ the same in the quasi-steady case. If you take into account kinetic energy added to the frame oscillation there can be a minute transient effect. Given the small masses and velocities involved, this effect is negligible.


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## stevesbike (Jun 3, 2002)

Pirx said:


> That's a neat example of how naïve intuition can go astray. "Available force" is not affected by frame flex. Frame flex or no, the force at the rear wheel is _exactly_ the same in the quasi-steady case. If you take into account kinetic energy added to the frame oscillation there can be a minute transient effect. Given the small masses and velocities involved, this effect is negligible.


10 pages later and you still haven't even mentioned, let alone attempt to defend, what's perhaps the most dubious claim in the history of cycling "science." Namely, Heine's claim that a flexy frame will "accept" 15% more power than a stiffer one. This is an under-estimate since the frames in his "study" were all relatively flexible compared to today's stiff carbon ones. Here's his statement:

"Imagine a bike that accepts extra power during the down stroke, rather than pushing back against your pedal stroke. Imagine that the frame stores the energy, and releases it at the end of your power stroke. This would lengthen the power phase of your stroke. Without having to accelerate the bike more, you would be able to put more power into it."

Here's the plot:








First off, this is one of the most non-reproducible claims in cycling. If it were true, today's Tour de France riders would be significantly slower than 80's era riders. Track riders today on the most stiff frames would likewise be significantly slower. It would mean Sean Kelly won his sprints because of his frames, not despite them. Of course, this isn't true. Track riders today reach top speeds no one did 20 years ago. It would mean I could turn pro if I could gain 15% more power just by riding my old Vitus. It would also mean I'm much slower on the track on my super-stiff track frame. Oddly, my power data shows no discrepancy between frames despite substantial variations in stiffness.

A potential 15% increase in power would also dwarf doping effects. It would be used by teams trying to gain small competitive advantages. Strange that no one seems to have discovered it. Since you think you're so much smarter than everyone else here, what are you doing wasting your time on a forum - you could be making millions turning cat 2s into world champions. Maybe the entire notion Heine claims - which you left off the original quotes from him - is just not true. The fact that the only thing you've mentioned is Heine's alternative view of bike frame efficiency isn't exactly a trump card considering the patently false conclusions he makes or the fact that frame stiffness optimization has been the design goal where it counts the most - on the track and even in BMX now that it's going to be an Olympic event. Do you have a shred of evidence that strain energy could result in a net increased in power?


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## Pirx (Aug 9, 2009)

stevesbike said:


> 10 pages later and you still haven't even mentioned, let alone attempt to defend, what's perhaps the most dubious claim in the history of cycling "science."


Gee, what do you think? Perhaps, it might just be that I have no interest whatsoever in this guy's claims; as you might have been able to figure out by now, if _you_ had any interest in an honest debate. I think I have stated what my assertion is very clearly, and I have done so repeatedly. I have also explained the status of that quote you love to drag out, in the context of my argument. So, if you want to address the claim _I_ am making, then I might be interested. Otherwise, you are of course free to keep bashing any silly straw you like, but you'll have to excuse me for not participating in that game.


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## davidka (Dec 12, 2001)

duriel said:


> I don't think you're getting it.
> 
> Energy is conserved, perfect.
> 
> But, with a flexy frame it limits the available force to the wheel as the frame flexes, thereby not allowing the available force of the foot to apply power.


The frame is less insignificant in the flex equation, unless the driveside chainstay is so flexible that it allows the distance from the crank to the rear axle to change.

A revolution of the crank is a fixed value.

If we wanted to address losses caused by flex, we'd work on the wheels.


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## Pirx (Aug 9, 2009)

davidka said:


> If we wanted to address losses caused by flex, we'd work on the wheels.


Please, let's not go there. That's vaguely the same story as with the frame (roughly, flex probably doesn't matter), but with some serious kinematical issues thrown in the mix that make it much harder to arrive at definite conclusions with any confidence the way this is possible for the frame. However, in the exact same way as for frame stiffness, no real evidence exists one way or another.

P.S.: There's a fairly neat article about wheel stiffness on slowtwitch.com, by the way. It doesn't really talk about performance implications at all, except for this interesting sentence: 



> On the flip side, you’re losing power by flexing a wheel or rubbing the brake pads.


While the brake pads part is fine, of course, the first part about "losing power by flexing the wheel" looks like it's based on the same naïve misconceptions that also underlie the debate in this thread. In simple words, no, it is not at all clear that "flexing the wheel" would cost you a significant amount of power. But, like I said, in this case I am much less confident in making a statement more definite than a vague "it's not clear"...

P.P.S.: This article seems to indicate that wheel stiffness doesn't matter for performance:



> Stiffness or deflection under load is the last performance variable I investigated, and it does not significantly affect performance unless brake pads rub the rim. However, some people simply prefer a stiffer wheel because the perception is that stiffer is better.


I do like that last sentence. :idea:


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## duriel (Oct 10, 2013)

nm nm nm


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## davidka (Dec 12, 2001)

Many wheels flex enough that under hard efforts, they rub the brake pads. 

I only meant to point out that being concerned about lateral frame flex when wheels can be deflected 2cm+ by *hand* is well, enough said..


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## aclinjury (Sep 12, 2011)

before this thread, I was still a little on the fence about companies' literatures regarding frame stiffness and performance. I hope by now, everyone in here realizes that the colorful powerpoint slides put out by Cervelo and Specialized and et al. have more input from the marketing dept than actual PhDs.

But after following what Pirx has said, I'm not left with any ambiguity when it comes to frame stiffness anymore. In a nutshell, it doesn't matter a damn! Pirx has raised enough questions and answered enough questions to convince me he knows his stuff. I'm going with him.

Now Stevesbike brought up some point in his thread above, namely he mentioned about the speed and finish time of the riders of the 80s versus riders of today. Then goes on to mention about the 15% energy absorption versus the 15% gain from doping. I guess Stevesbike is alluding to the notion that all these may be what makes the difference in speed of the 80s versus today. Well, this is a very, very, very, gross jump of conclusion based on very, very, loose and contentious assumptions. Not what you want to base your debate on which you're trying to make it look rigorous.

But I'd also like to add one thing about frame flexing. And that is frame flexing probably affect a bike's handling/cornering performance (especially during a fast descent) much more than it does on the efficiency of power delivery.


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## goodboyr (Apr 19, 2006)

aclinjury said:


> before this thread, I was still a little on the fence about companies' literatures regarding frame stiffness and performance. I hope by now, everyone in here realizes that the colorful powerpoint slides put out by Cervelo and Specialized and et al. have more input from the marketing dept than actual PhDs.
> 
> But after following what Pirx has said, I'm not left with any ambiguity when it comes to frame stiffness anymore. In a nutshell, it doesn't matter a damn! Pirx has raised enough questions and answered enough questions to convince me he knows his stuff. I'm going with him.
> 
> ...


Please show me the cervelo slide that claims stiffness equals more energy.....


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## duriel (Oct 10, 2013)

Yes, page after page of smoke, so he must be right.

At the pro level a stiff bike is faster, he has not proved otherwise. For weekend joe, I'll concede that there is not much to be gained there.


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## OldChipper (May 15, 2011)

Pirx said:


> If some of the energy input by the rider is used to temporarily flex the frame, once the frame un-flexes the energy is returned. All of it. No energy is lost. None. At. All.


Well, at least in detail, you're wrong. A bicycle frame is not a perfect spring ergo, SOME energy IS lost - likely converted to heat assuming the the frame is not permanently deformed at all or no carbon fibers break. Further that return spring force is not converted into propulsive force, so energy that flexes the frame rather than driving the wheel IS propulsive force lost. Now, whether these amounts of "lost," would better be termed: "wasted," energy is significant in the range of rigidity of bike frames is an open question - at least to me.


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## PBL450 (Apr 12, 2014)

aclinjury said:


> before this thread, I was still a little on the fence about companies' literatures regarding frame stiffness and performance. I hope by now, everyone in here realizes that the colorful powerpoint slides put out by Cervelo and Specialized and et al. have more input from the marketing dept than actual PhDs.
> 
> But after following what Pirx has said, I'm not left with any ambiguity when it comes to frame stiffness anymore. In a nutshell, it doesn't matter a damn! Pirx has raised enough questions and answered enough questions to convince me he knows his stuff. I'm going with him.
> 
> ...


I couldn't agree more... Now, shoe flex, that's a whole other story. If the sole bends over the fulcrum of the pedal you just bleed power. A rigid sole is worth massive watts.


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## myhui (Aug 11, 2012)

OldChipper said:


> Well, at least in detail, you're wrong. A bicycle frame is not a perfect spring ergo, SOME energy IS lost - likely converted to heat assuming the the frame is not permanently deformed at all or no carbon fibers break.


Quite right! Quite right!

( triple face palm for @Pirx )


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## ibericb (Oct 28, 2014)

duriel said:


> At the pro level a stiff bike is faster, he has not proved otherwise.


You've repeatedly asserted that a "stiff bike" is faster, as if stiffness is an absolute. It's not. Stiffness is relative. 

It's never been proven, by anyone, that stiffer is faster. Even Damon Rinard, who at one time tried to make the case for stiffer, admits it is an insignificant effect. As he states, he would look elsewhere for speed.


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## davidka (Dec 12, 2001)

PBL450 said:


> I couldn't agree more... Now, shoe flex, that's a whole other story. If the sole bends over the fulcrum of the pedal you just bleed power. A rigid sole is worth massive watts.


Even Sidi once asserted that a completely stiff shoe wasn't optimal, because the foot is not meant to be held completely static. There's a lot of moving parts in a foot. Many people can't get used to having them all held too still.

Based on what's on the market today, I'd say the marketers have won. The marketers give the Kool-Aid and if it tastes good enough, the market starts making its own.


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## Pirx (Aug 9, 2009)

duriel said:


> At the pro level a stiff bike is faster, he has not proved otherwise.


I don't need to. You are the one making the positive assertion. Do you happen to have any proof, anything at all to back up that fantastic claim of yours? No? That's what I thought. Like I said, your claim is just as valid as the one of somebody asserting that red bikes are faster. 



OldChipper said:


> Well, at least in detail, you're wrong. A bicycle frame is not a perfect spring ergo, SOME energy IS lost - likely converted to heat assuming the the frame is not permanently deformed at all or no carbon fibers break. Further that return spring force is not converted into propulsive force, so energy that flexes the frame rather than driving the wheel IS propulsive force lost. Now, whether these amounts of "lost," would better be termed: "wasted," energy is significant in the range of rigidity of bike frames is an open question - at least to me.


You're coming in late to the party. In brief, yep, some power is converted into heat, and that is indeed lost. A rough estimate of that is of the order of one tenth of a watt, maximum, during a hard sprint (say, 1kW). Feel free to worry about that one if you like. 

Other than that, no, energy that flexes the frame in a reversible manner is NOT lost and can indeed be converted back into a propulsive force. You may want to read the material that has been posted as well as linked to on that subject. We've gone over that ground so often by now that there's really no justification for rehashing this stuff.



myhui said:


> Quite right! Quite right!
> 
> ( triple face palm for @Pirx )


What's that noise in the background? Did somebody say something?


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## crit_boy (Aug 6, 2013)

interesting that we immediately concede that a wheel flexing enough to hit the brake is flexible enough to represent wasted power. But, still conclude flexy frames may be OK - while ignoring that flexy frames cause the chain to rub the front derailleur. 

post hole digger research often falls short in the real world.


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## ibericb (Oct 28, 2014)

crit_boy said:


> interesting that we immediately concede that a wheel flexing enough to hit the brake is flexible enough to represent wasted power.


You need to catch up a bit. When the rim rubs the brake it usually due to greater wheel stiffness, not flexing. Adequate wheel flexing keeps the rims from rubbing the brake. Did you miss that part of the discussion?


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## Pirx (Aug 9, 2009)

crit_boy said:


> interesting that we immediately concede that a wheel flexing enough to hit the brake is flexible enough to represent wasted power.


Where did you get that idea? Yes, brake rub obviously results in wasted power. How much is hard to tell, and obviously depends on the amount of rub. Note that it seems brake rub is created by rims that are very stiff, see the link I had provided. Without brake rub, it's not clear if wheel flex has any significant consequences on power.



crit_boy said:


> But, still conclude flexy frames may be OK - while ignoring that flexy frames cause the chain to rub the front derailleur.


All we're doing here is trying to separate completely different effects from each other. The claim we have been discussing is that frame flex, in and of itself, equals lost energy. You're now trying to drag the discussion into a different question, namely the effect of FD rub. Well, first of all, there's many, many frames that flex without leading to a rubbing derailleur. As a matter of fact, I have never had my FD rub on any of my bikes, steel or carbon, "flexy" or (fairly) stiff. Second, given the very low coefficient of friction between a lubed chain and the FD plate, I would expect that in all but the most extreme cases the power lost via FD rubbing to be very small. But, sure, it depends. The main point is, that's an entirely different question. Just adjust your damn derailleur properly.



crit_boy said:


> post hole digger research often falls short in the real world.


Sure, sure.


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## Pirx (Aug 9, 2009)

aclinjury said:


> But I'd also like to add one thing about frame flexing. And that is frame flexing probably affect a bike's handling/cornering performance (especially during a fast descent) much more than it does on the efficiency of power delivery.


Sorry, I almost overlooked this last paragraph. Yes, this is a very good point: There may well be very good reasons to prefer (laterally) stiff frames, including stability, or even just subjective feel. There is absolutely nothing wrong with any of this, and if indeed people prefer the "feel" of the laterally stiffer frame, or the stiffer BB, then, sure, that's what the industry should strive to provide. It's just like if everyone prefers red bikes, then that's what manufacturers should, and will sell to customers. 

As a matter of fact, I understand quite well the allure of the feeling of a frame that does not flex under power, and I like it myself. However, I do not confuse feelings of that kind with the cold, hard facts regarding energy efficiency. But, let me repeat, if everybody, or even just a few riders, prefer stiffer frames, then they don't need to invent excuses for such a preference. Least of all do they need an excuse that does not correlate to physical fact.


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## aclinjury (Sep 12, 2011)

duriel said:


> Yes, page after page of smoke, so he must be right.
> 
> At the pro level a stiff bike is faster, he has not proved otherwise. For weekend joe, I'll concede that there is not much to be gained there.


He's shown me more than you. You want to show us you understand the physics we're talking about more than Pirx? So far, none in here has shown this.


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## aclinjury (Sep 12, 2011)

Pirx said:


> Sorry, I almost overlooked this last paragraph. Yes, this is a very good point: There may well be very good reasons to prefer (laterally) stiff frames, including stability, or even just subjective feel. There is absolutely nothing wrong with any of this, and if indeed people prefer the "feel" of the laterally stiffer frame, or the stiffer BB, then, sure, that's what the industry should strive to provide. It's just like if everyone prefers red bikes, then that's what manufacturers should, and will sell to customers.
> 
> As a matter of fact, I understand quite well the allure of the feeling of a frame that does not flex under power, and I like it myself. However, I do not confuse feelings of that kind with the cold, hard facts regarding energy efficiency. But, let me repeat, if everybody, or even just a few riders, prefer stiffer frames, then they don't need to invent excuses for such a preference. Least of all do they need an excuse that does not correlate to physical fact.


yep. And I don't mean to imply that a stiff frame is always best for all rider in descending. Personally I love the flexy suppleness of a steel frame on the descent. Carbon frames, to me, is stiff and tend to bounce around in corner, where as steel stays planted. There are other factors at play too, such as tires, rider's skills, but I always prefer the suppleness of steel over carbon on the descent any day.

now on a sort of related note. Remember that Olympic 400m sprinter Oscar Pistorius with prostetic legs? After his performance at the Olympics, people immediately questioned whether the spring property of his prostetic actually gave him an advantage over human legs. I'm pretty damn sure they did! He ran on those plastic legs like he was gliding on them, so smooth and fluid, that his body was not even bobbing up and down. That's return energy right there!


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## froze (Sep 15, 2002)

So a better bike would be to have Walmart build a cheap light and aero frame that will flex along with flexy wheels and this bike will become the norm in pro races from now on. Just think how much money all these pro teams can save which would surely open the doors for less fortunate people who always wanted to race but found it too expensive.


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## crit_boy (Aug 6, 2013)

Pirx said:


> As a matter of fact, I have never had my FD rub on any of my bikes, steel or carbon, "flexy" or (fairly) stiff. Second, given the very low coefficient of friction between a lubed chain and the FD plate, I would expect that in all but the most extreme cases the power lost via FD rubbing to be very small. But, sure, it depends. The main point is, that's an entirely different question. Just adjust your damn derailleur properly.


It is not a derailleur adjustment issue. It is an issue with the bb moving like a nutating disc. I have a bike i no longer ride b/c i can readily put out enough power to cause the derailleur to rub. i can flex something (chainrings or bb don't know) enough to get rubbing on my venge too. but, that doesn't happen until more than 700 or 800 watts. so it is much less regular. 

My point is that a frame that flexes enough to allow the front mech to rub is causing power loss - in the real world.


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## Pirx (Aug 9, 2009)

crit_boy said:


> i can flex something (chainrings or bb don't know) enough to get rubbing on my venge too. but, that doesn't happen until more than 700 or 800 watts. so it is much less regular.


I top out at around 1000 watts these days (yeah, I am getting old...), and my FD doesn't rub, ever, even on my 1980s steel bike. If you get rubbing, it's most likely caused by deformation of the rear triangle, not the BB. In other words, it's not the chainring moving relative to the FD that's the issue (that motion is likely too little to cause a problem), but it's the chainline moving due to the motion of the rear triangle.



crit_boy said:


> My point is that a frame that flexes enough to allow the front mech to rub is causing power loss - in the real world.


That's possible, sure, but like I said it's an effect that I'm not interested in in this discussion. First of all, it's an effect that only occurs for certain setups (and gear combinations) and is not a function of frame flex alone. Second, whether or not the amount of power consumed by friction between the chain and the FD is significant is an open question, and finally, it's a very rare event in any case.


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## Pirx (Aug 9, 2009)

froze said:


> So a better bike would be to have Walmart build a cheap light and aero frame that will flex along with flexy wheels and this bike will become the norm in pro races from now on.


Nonsense.


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## aclinjury (Sep 12, 2011)

froze said:


> So a better bike would be to have Walmart build a cheap light and aero frame that will flex along with flexy wheels and this bike will become the norm in pro races from now on. Just think how much money all these pro teams can save which would surely open the doors for less fortunate people who always wanted to race but found it too expensive.


there are A LOT of instances in other industries, where a lot of bright minds exist, where for years people held onto a belief or notion of doing things,, until one day they discovered that belief or notion wasn't as what they had thought. Then the moved on. People tend to think like a herd sometimes, maybe because it's tradition, maybe because they're just lazy, but yep, even the smart ones think like a herd sometimes too. The difference between the smart ones and the dumb ones is that the smart ones will eventually figure it out, while the dumb ones will keep repeating the same ole herd mentality.

But really, at this point, in this thread, you should either debate Pirx's contention in frame flex directly, and preferably at his level, or sit tight and listen. Throwing a silly jab is weak sauce.


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## myhui (Aug 11, 2012)

aclinjury said:


> People tend to think like a herd sometimes, maybe because it's tradition, maybe because they're just lazy, but yep, even the smart ones think like a herd sometimes too.


So true!


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## Jwiffle (Mar 18, 2005)

One thing I haven't seen mentioned is that you pedal on both sides of the bike. We've discussed how the frame can recover the energy used in being flexed when it springs back. But it does more than just spring back, no? It gets flexed back the other way when you pedal the crank. So the sideways force would be pretty much cancelled out. So flex would then have pretty much no effect on power transfer to the rear wheel.


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## duriel (Oct 10, 2013)

Jwiffle said:


> One thing I haven't seen mentioned is that you pedal on both sides of the bike. We've discussed how the frame can recover the energy used in being flexed when it springs back. But it does more than just spring back, no? It gets flexed back the other way when you pedal the crank. So the sideways force would be pretty much cancelled out. So flex would then have pretty much no effect on power transfer to the rear wheel.


seriously?


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## Jwiffle (Mar 18, 2005)

duriel said:


> seriously?


Yes, seriously. Look, my understanding of physics nowhere near matches Pirx's or others in here, but I have enough to understand you can't just believe manufacturers' marketing claims, which so far have been your only basis for your belief that stiffness equals power. There is that whole "for every action there is an equal and opposite reaction" thing weighing in favor of the augment that frame stiffness means little for power transfer.

Again, I have yet to see it be proved that the force causing the frame to be flexed even COULD be used for power transfer. Power that drives the crank around is in a circular plane (well, pretty much a portion of the circle, since it's rare to actual pedal full circles). Sideways forces that occur seem like they'll remain the same, whether it flexes the frame or not. (Push hard on a slightly open door, and it flies open; same push on a locked door, it doesn't move. Neither push adds or subtracts from the force of gravity pulling down on the door)


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## froze (Sep 15, 2002)

crit_boy said:


> It is not a derailleur adjustment issue. It is an issue with the bb moving like a nutating disc. I have a bike i no longer ride b/c i can readily put out enough power to cause the derailleur to rub. i can flex something (chainrings or bb don't know) enough to get rubbing on my venge too. but, that doesn't happen until more than 700 or 800 watts. so it is much less regular.
> 
> My point is that a frame that flexes enough to allow the front mech to rub is causing power loss - in the real world.


I've either had frames that would rub the FD or test rode ones that did. My first real road bike, a 1976 Trek TX900 rubbed but I heard all frames back then did and I believe they did, some worse than others like French frames. Now that I no longer race and my power has dropped due to age and not training like I use to and since moving from a mountainous area to mostly flat lands I can't get any of my frames to flex so now I no longer care.

I think the flexing BB is a source of power loss, it has always been widely held by pros and frame builders that this was the case, if not then like I said earlier just have Walmart make a cheap light aero flexy frame and away we go.


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## duriel (Oct 10, 2013)

This is why stiff frames are faster..... pay attention.
Say Pro Rider A can push 250 lbs on the pedal. 
Lets examine 2 frames, frame A bends substantially @ 150lbs and frame B bends @ 300lbs. 
When Pro Rider A pushes on the pedal on bike A, the maximum force he can push is 150lbs, and thereby moves forward with that associated torque on the rear wheel.
When Pro Rider A pushes on the pedal on bike B, the maximum force he can push is 250lbs, and thereby moves forward with that associated torque on the rear wheel.
Bike B will move away faster.

Wait, did I say faster?


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## froze (Sep 15, 2002)

aclinjury said:


> there are A LOT of instances in other industries, where a lot of bright minds exist, where for years people held onto a belief or notion of doing things,, until one day they discovered that belief or notion wasn't as what they had thought. Then the moved on. People tend to think like a herd sometimes, maybe because it's tradition, maybe because they're just lazy, but yep, even the smart ones think like a herd sometimes too. The difference between the smart ones and the dumb ones is that the smart ones will eventually figure it out, while the dumb ones will keep repeating the same ole herd mentality.
> 
> But really, at this point, in this thread, you should either debate Pirx's contention in frame flex directly, and preferably at his level, or sit tight and listen. Throwing a silly jab is weak sauce.


You need to sit tight and listen because you're failing big time at this. I think years of industry knowledge on this subject dwarfs whatever you think you can bring to this conversation.


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## Jwiffle (Mar 18, 2005)

duriel said:


> This is why stiff frames are faster..... pay attention.
> Say Pro Rider A can push 250 lbs on the pedal.
> Lets examine 2 frames, frame A bends substantially @ 150lbs and frame B bends @ 300lbs.
> When Pro Rider A pushes on the pedal on bike A, the maximum force he can push is 150lbs, and thereby moves forward with that associated torque on the rear wheel.
> ...


That makes no sense.


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## davidka (Dec 12, 2001)

crit_boy said:


> My point is that a frame that flexes enough to allow the front mech to rub is causing power loss - in the real world.


THe point being driven in this thread is that the flex you're talking about does not cause any meaningful power loss, in the real world. 



froze said:


> You need to sit tight and listen because you're failing big time at this. I think years of industry knowledge on this subject dwarfs whatever you think you can bring to this conversation.


Years of industry knowledge (which I also have), is completely meaningless in this conversation, unless that experience was focused specifically on engineering racing frames. Mine hasn't been, has yours?


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## ibericb (Oct 28, 2014)

froze said:


> You need to sit tight and listen because you're failing big time at this. I think years of industry knowledge on this subject dwarfs whatever you think you can bring to this conversation.


Right, and the "industry knowledge" that has actually sought to measure the effect and determine the importance of frame stiffness on the delivery of propulsive power to the rear wheel has found that frame stiffness, within the range of common frame materials does not matter. There have been numerous citations within this thread to those determinations of fact. That actual knowledge, based on real facts, dwarfs your misguided beliefs and assertions.


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## ibericb (Oct 28, 2014)

Jwiffle is correct - your analysis makes absolutely no sense. You can make up nonsense all day long, and convince yourself it's real. It is now clear that you have no grasp of the fundamental physics involved. None whatsoever.


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## Mandeville (Oct 18, 2014)

The difference in power if any at all regarding the BB is irrelevant to me as I lack the power to take advantage of any potential or possible difference. 

However, the thread as a whole truly represents the good, the bad, and the ugly and then some of a posting forum.


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## aclinjury (Sep 12, 2011)

froze said:


> You need to sit tight and listen because you're failing big time at this. I think years of industry knowledge on this subject dwarfs whatever you think you can bring to this conversation.


I admit I don't have the expertise to contribute much technical to this convo. But you don't have the expertise neither, yet you chose to contribute nonsense to the thread. Why?

And btw, years of industry knowledge means jack if they have been doing it wrong for years. And we know people can get into a herd mentality and they just keep doing (or thinking) the wrong thing over and over. Duh. Ok.


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## duriel (Oct 10, 2013)

Please take all your information, texts, papers, "printouts off the internet forums", & you'll need some pictures on down and into Felt's corporate office. Lay it on the table.... 

They will have the niche at just the right time, now that you have proven beyond all doubt that "Flexi is the new Bike"!

They might want to change the name of the company after you get them in the right direction.


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## ibericb (Oct 28, 2014)

duriel said:


> Please take all your information, texts, papers, "printouts off the internet forums", & you'll need some pictures on down and into Felt's corporate office. Lay it on the table....
> 
> They will have the niche at just the right time, now that you have proven beyond all doubt that "Flexi is the new Bike"!
> 
> They might want to change the name of the company after you get them in the right direction.


Now you are just creating more nonsense. Nobody other than you suggested "flexi is the new bike". Apparently you've missed the entire discussion, as well as not understanding any of the physics involved.

BTW - maybe you should look back within this thread to find reference to what Damon Rinard concluded from thier reserch when he was at Cervelo.


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## OldChipper (May 15, 2011)

Pirx said:


> You're coming in late to the party. In brief, yep, some power is converted into heat, and that is indeed lost. A rough estimate of that is of the order of one tenth of a watt, maximum, during a hard sprint (say, 1kW). Feel free to worry about that one if you like.
> 
> Other than that, no, energy that flexes the frame in a reversible manner is NOT lost and can indeed be converted back into a propulsive force. You may want to read the material that has been posted as well as linked to on that subject. We've gone over that ground so often by now that there's really no justification for rehashing this stuff.


Well at least this linked article: https://janheine.wordpress.com/2014/12/31/the-biomechanics-of-planing/

reads like so much hand-waving BS (kind of like explanations of how homeopathy "works"). Lots of assertions, feelings, and pretty drawings but no explanations or data. I don't see how a linear force that causes lateral frame flex can be converted into a rotational force on either the drive train or the rear wheel - one of which is absolutely required for your assertion to be true. 

I will grant you that energy expended flexing the BB back and forth isn't "lost," it just doesn't move the bike down the road. 

Finite element analysis and linked articles aside, if flexy frames were faster and more or equally efficient, the pros would be riding them. They spend big for fractional gains. Also how do you explain the extreme case which reduces your argument to absurdity i.e. a frame made our of hardware store PVC tubing? Is your assertion that such a super flexy frame is just as or more efficient than a $10K carbon superbike? If not, then were is the magical point where flexiness is no longer an issue?


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## Pirx (Aug 9, 2009)

OldChipper said:


> Well at least this linked article: https://janheine.wordpress.com/2014/12/31/the-biomechanics-of-planing/
> 
> reads like so much hand-waving BS (kind of like explanations of how homeopathy "works"). Lots of assertions, feelings, and pretty drawings but no explanations or data.


Funny how you pick that one of all the material that has been posted. But, yes, I quoted the guy in my very first post, purely as an illustration, and I deeply regret that I brought him up. I will not edit that first post, however, since that might distort the record. Suffice it to say that many of the opinions of this guy are not representative of mine, at all, beyond the most basic parallels. Feel free to critique his opinions all day long if you like, but be aware that you're beating up a straw man.



OldChipper said:


> I don't see how a linear force that causes lateral frame flex can be converted into a rotational force on either the drive train or the rear wheel - one of which is absolutely required for your assertion to be true.


That's been discussed and explained, including links to a detailed study of just that question. Just read the damn thread. I have lost patience with people waltzing in here that are too lazy to even understand what the claims are or even just what the discussion is about, and I'll be damned if I keep going over the same ground over and over again. :mad2:



OldChipper said:


> Also how do you explain the extreme case which reduces your argument to absurdity i.e. a frame made our of hardware store PVC tubing? Is your assertion that such a super flexy frame is just as or more efficient than a $10K carbon superbike?


Oh please, don't play stupid with me. Of course not, as you would know if you had read what I had written.



OldChipper said:


> If not, then were is the magical point where flexiness is no longer an issue?


The answer is obvious from the material in this thread also: We need to assume fully elastic deformation. Your hardware store PVC would show plastic deformation, at which point our fundamental energy conservation goes out the window. In addition, even for the fully elastic case things become dicey when we allow very large, nonlinear deformation (say, a "bicycle frame" made out of very thin steel rods). In this case you would see significant changes in geometry which would have all sorts of consequences for the bike and rider. Obviously none of these cases are of any practical interest. I stated, at the very beginning of this thread, that we restrict ourselves to at least halfway realistic road bikes, built within the last 30 years or so. Is that clear enough now?


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## crit_boy (Aug 6, 2013)

Pirx said:


> As a consequence, it may well be that some riders do better on more flexible frames, and some others may prefer stiffer ones. Bottom line: Nobody knows, and all the rest is nothing but clueless babble.


Post #1 should have been the beginning and end.

Want to buy a flexy Rivendale (source of OP's material is a seller of flexible frames - yet somehow an objective source) that permits the rider to magically make 15% more power faster than a stiff framed marketing scam? Go to it. 

Want to buy the stiffest frame ever conceived? Go to it.

Personal preference. End of.


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## Pirx (Aug 9, 2009)

crit_boy said:


> source of OP's material is a seller of flexible frames


Come again? The above is either indicative of complete idiocy, or a flat-out, bald-faced lie. Let me spell this out for you: Heine is the source of exactly zero of my material beyond that quote of his I had included. The only objective source in this discussion is the science of physics.


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## ibericb (Oct 28, 2014)

A related question - when did BQ or or Compass Bicycles or Jan Heine become "a seller of flexible frames"?


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## aclinjury (Sep 12, 2011)

duriel said:


> Please take all your information, texts, papers, "printouts off the internet forums", & you'll need some pictures on down and into Felt's corporate office. Lay it on the table....
> 
> They will have the niche at just the right time, now that you have proven beyond all doubt that "Flexi is the new Bike"!
> 
> They might want to change the name of the company after you get them in the right direction.


I'm willing to bet a PhD gets paid more at an aerospace/defense contractor firm than at Felt. Do they even have PhDs at Felt? Maybe 1? Oh please.


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## tvad (Aug 31, 2003)

This whole thread seems like a justification by a couple of old guys to legitimize their preference for old school flexible steel frames, and to indirectly label owners of more modern carbon frames as fools. 

No need. 

Ride what you like. 

Let others ride what they like. 

Why piss on something people enjoy? I don't see the point other than an exercise in superiority in a specific field of study. 

What's next, a debate about the superiority of black and white televisions or ice boxes?


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## aclinjury (Sep 12, 2011)

tvad said:


> This whole thread seems like a justification by a couple of old guys to legitimize their preference for old school flexible steel frames.
> 
> No need.
> 
> ...


couple old guys?? And how young are you, stud?

edit (since you edited): they didn't piss on anyone. They posted a legit topic on an open forum. Then some people who don't understand physics came in only to find themselves in a world of butt hurt because they're told they don't know what they're talking about, which is validated with their nonsensical posts after posts. Be glad some smart folks are willing to donate their time to educate you.


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## Pirx (Aug 9, 2009)

tvad said:


> This whole thread seems like a justification by a couple of old guys to legitimize their preference for old school flexible steel frames.


For the record, I ride a Felt F1, and love it. 



tvad said:


> Ride what you like.
> 
> Let others ride what they like.


I couldn't agree more.



tvad said:


> Why piss on something people enjoy?


Who is "pissing" on anything? Can you point out one instance, just a single one, where I or anybody else has said anything negative about (laterally) stiff frames? Are you saying that, after 280+ posts in this thread you still have no clue what it is we are talking about? Do I really have to spell it out again just for you, for the umpteenth time now? Sheesh...


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## tvad (Aug 31, 2003)

aclinjury said:


> couple old guys?? And how young are you, stud?


I'm young enough to enjoy the new fangled stuff made after 1989.


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## ibericb (Oct 28, 2014)

tvad said:


> This whole thread seems like a justification by a couple of old guys to legitimize their preference for old school flexible steel frames.


I don't recall anyone attempting to justify any preference, at all. The point was the notion that a stiffer frame leads necessarily to greater power at the real wheel simply because it is stiffer is a false one. That's it. There was no advocacy for stiffer or less stiff, steel, carbon or other frame material.




> Ride what you like.
> 
> Let others ride what they like.


Yep. That point was made several times by the OP, and joined by others who actually understood the point, which clearly you missed.



> I don't see the point ...


Clearly, you don't.


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## aclinjury (Sep 12, 2011)

tvad said:


> I'm young enough to enjoy the new fangled stuff made after 1989.


I expected more from a guy your age and wisdom.


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## tvad (Aug 31, 2003)

Pirx said:


> Can you point out one instance, just a single one, where I or anybody else has said anything negative about (laterally) stiff frames?


How about the first sentence of your first post?


> This is somewhat of an old topic, and I think by now many of us understand that *the still ongoing obsession with frame stiffness, in the form of "lateral stiffness"*, "stiff bottom brackets", etc., etc., *is nothing but marketing BS.*


Game over.


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## crit_boy (Aug 6, 2013)

Pirx said:


> Come again? The above is either indicative of complete idiocy, or a flat-out, bald-faced lie. Let me spell this out for you: Heine is the source of exactly zero of my material beyond that quote of his I had included. The only objective source in this discussion is the science of physics.


The entire basis of your OP was a link from "_News from Bicycle Quarterly and Compass Bicycles" _by Jan Heine. Maybe look back at your OP. 

Throughout the thread, when confronted with objective discussion, you have dismissed it as not a significant source of power loss. While these examples cannot make up the "real physics" (AKA magical) 15% power gain of a flexible frame, they do represent some form of power loss. 

I did make the mistake of thinking compass bikes sold frames to go with their old-timey clothing, bars, cranks, bags, fenders, etc. 

Once again ride what you like. You like flexible frames. Great, go to it. Spend your money and time on what makes you happy and I'll do the same.


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## velodog (Sep 26, 2007)

I don't understand the anger that seems to be coming from the stiffer is better crowd, all the while professing that we should ride what we want. No one ever said anything different, just that much of the stiffness claim is marketing, so why all the emotion?

It seems like someone needs to get together a crank based power meter and a wheel based unit and compare wattages from one end to the other on a good plastic bike, and then on a good steel bike, and compare apples to apples.

The stiffer is better bunch could bring that to the table to prove their point.

Or just stay upset because they feel that someone is dissing their bicycle choice.


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## froze (Sep 15, 2002)

aclinjury said:


> I admit I don't have the expertise to contribute much technical to this convo. But you don't have the expertise neither, yet you chose to contribute nonsense to the thread. Why?
> 
> And btw, years of industry knowledge means jack if they have been doing it wrong for years. And we know people can get into a herd mentality and they just keep doing (or thinking) the wrong thing over and over. Duh. Ok.



I guess if you can contribute nonsense then so can I. herd mentality isn't always wrong, there are a lot of herd mentality that is correct, so just because the herd believes the earth is round doesn't mean its flat because someone read one or two studies claiming it's flat and thus the herd mentality is incorrect. See how nonsensical you sound? of course not because you believe the earth is flat and nothing anyone can say is going to change that.


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## velodog (Sep 26, 2007)

crit_boy said:


> I did make the mistake of thinking compass bikes sold frames to go with their old-timey clothing, bars, cranks, bags, fenders, etc.


So, just an assumption?

Your only one?


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## Pirx (Aug 9, 2009)

tvad said:


> How about the first sentence of your first post?
> 
> 
> 
> ...


Perhaps you don't speak English? Or you speak a language that uses the same words as we do in English, but the words have different meanings? Try as I might, there is nothing in that quote that says anything negative about stiff frames. It does say something about the _obsession_ with stiff frames (as being superior performance-wise). Do you understand the difference?

As a matter of psychopathology, I am in fact more interested in the question of why you have the need to insist that I am dissing stiff frames, even after I have repeatedly stated that I have no objection against them, just as I have no objection against red frames.



crit_boy said:


> The entire basis of your OP was a link from "_News from Bicycle Quarterly and Compass Bicycles" _by Jan Heine. Maybe look back at your OP.


Another guy with reading comprehension problems. I have already explained this, however, so I won't go over it again. Feel free to go back to my OP, and read the second paragraph. Try to understand what it says, please.



crit_boy said:


> Throughout the thread, when confronted with objective discussion, you have dismissed it as not a significant source of power loss. While these examples cannot make up the "real physics" (AKA magical) 15% power gain of a flexible frame, they do represent some form of power loss.


I have trouble parsing your sentences above. No matter, if you're trying to say that I have not provided an objective basis for my position, you either have not read what I wrote, have not understood it, or you're being dishonest. Take your pick.

As for Heine's other claims (leaving open what exactly those are; I note in passing that those are being misrepresented as well, but that's not my interest here), I have no interest in them, as I have explained before. Same advice as to the other poster above: Feel free to make yourself look silly by bashing that straw man.



crit_boy said:


> Once again ride what you like. You like flexible frames. Great, go to it. Spend your money and time on what makes you happy and I'll do the same.


So you didn't get that part, either, huh? Actually, I do like stiff frames myself, but that preference has nothing to do with any imagined performance benefits.


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## Pirx (Aug 9, 2009)

velodog said:


> I don't understand the anger that seems to be coming from the stiffer is better crowd, all the while professing that we should ride what we want. No one ever said anything different, just that much of the stiffness claim is marketing, so why all the emotion?


Thanks very much for restating the point of all this. 

And, yes, I'm really starting to become more interested in those fascinating strong emotions that people bring to this debate, which clearly cloud their understanding of what is being said. Where do those feelings come from? Is it something as simple as "Now that I've spent five grand on that brand new 2015 frame that's "30% stiffer in the bottom bracket" than my old one, this guy comes along and says it won't make me any faster, so I wasted all this money"? Actually, I doubt that it's that, but what is it, then?


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## ibericb (Oct 28, 2014)

crit_boy said:


> .... While these examples cannot make up the "real physics" (AKA magical) 15% power gain of a flexible frame, they do represent some form of power loss.


There was no "magical 15% power gain of a flexible frame", nor was there a loss in the stiff frame. You clearly missed Heine's point from those tests, just as you have completely missed the OP's point in this thread. Those points are not the same, at all, but the outcomes may have some similarities.



> Once again ride what you like. You like flexible frames. Great, go to it. Spend your money and time on what makes you happy and I'll do the same.


I don't believe flexible frames were ever advocated or noted as favored. Once again, you've missed the central point entirely. Take solace in the fact that you are not alone, as evidenced by the comparable miss by others.


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## ibericb (Oct 28, 2014)

Pirx said:


> ... Actually, I doubt that it's that, but what is it, then?


Comprehension, either reading or subject matter knowledge?


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## aclinjury (Sep 12, 2011)

froze said:


> I guess if you can contribute nonsense then so can I. herd mentality isn't always wrong, there are a lot of herd mentality that is correct, so just because the herd believes the earth is round doesn't mean its flat because someone read one or two studies claiming it's flat and thus the herd mentality is incorrect. See how nonsensical you sound? of course not because you believe the earth is flat and nothing anyone can say is going to change that.


You're a person in his 60s right? You have nothing to contribute, know nothing, but good at dishing nonsense. Act your age man, please. Tell you what, if Stphen Hawking can be wrong about black holes (after pretty much his entire career), then you hell can bet Joe Schmoe's belief in frame stiffness in regard to energy transfer can also be wrong too.


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## aclinjury (Sep 12, 2011)

Pirx said:


> Thanks very much for restating the point of all this.
> 
> And, yes, I'm really starting to become more interested in those fascinating strong emotions that people bring to this debate, which clearly cloud their understanding of what is being said. Where do those feelings come from? Is it something as simple as "Now that I've spent five grand on that brand new 2015 frame that's "30% stiffer in the bottom bracket" than my old one, this guy comes along and says it won't make me any faster, so I wasted all this money"? Actually, I doubt that it's that, but what is it, then?


It's a combination of all those. You probably know in science once a belief is entrenched, then it will tend to stay until someone comes along to shed light on it, and even then, it will take some contentious time before people will let go of such belief. Same with life, the internet. The fact of the matter is, most of those who post nonsense in here, most of those who keep asking or repeating what already been said in here, most of these guys ain't trained and don't have the knowledge like you buddy. They can only grasp and appreciate maybe, maybe 1/4 of what you said. Ugh that's why they kept repeating the same old, because they don't understand the basic principles from the get go. Duh. I doubt most even bother to read any articles you linked, and even if they did, they may get maybe 1/10th. Their entire understanding of frame stiffness in relation to bicycle performance is based on... spoon fed to them.. by the bigs,.. the Specialized and Cervelo MARKETING literatures. And now here you are pal coming along to waltz all over their now endeared marketing literatures. Of course their initial reaction to rebel, question your authority, and when that fails, start to attack your snobby academic bowtie wearing attitude! Oh dear, I don't want to sound like I'm some pyschologist but you get my drift.


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## goodboyr (Apr 19, 2006)

You've mentioned cervelo again. Please show me where cervelo ever stated that you get more power from a stiffer frame.


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## aclinjury (Sep 12, 2011)

goodboyr said:


> You've mentioned cervelo again. Please show me where cervelo ever stated that you get more power from a stiffer frame.


they never said more power from stiffer frame (as even they know it ain't true). But their literature and a youtube vid implicated that "better performance" (whatever that means), oh most definitely full of half-science and half-marketing stuff. blah blah honestly at this point in this thread, so much more rigor has been enlightened to me in here that I have low interest in searching for the Cervelo stuff again, but it's out there if you want to google. Me, i'm more interested in what the two old guys Pirx and Iberic have been telling so far


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## ibericb (Oct 28, 2014)

Just for the record, since it was raised by someone flinging misguided ideas about old guys and steel frames around, my last steel frame (1989 Raleigh Competition) went to the curb for recycle two years ago. Since then it's been a carbon Domane. 

Stiffness is relative, not absolute. Pick what works for you, for whatever reason. If you're faster on stiffer, and that's what you like, ride it. Just don't believe it's because the stiffer frame is more efficient at transferring power from the rider to the rear wheel. If you are faster on stiffer, that's not the reason.


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## tvad (Aug 31, 2003)

ibericb said:


> Just for the record, since it was raised by someone flinging misguided ideas about old guys and steel frames around, my last steel frame (1989 Raleigh Competition) went to the curb for recycle two years ago. Since then it's been a carbon Domane.


You are a practical man. What was the reason for the carbon Domane purchase?


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## ibericb (Oct 28, 2014)

tvad said:


> You are a practical man. What was the reason for the carbon Domane purchase?


It meets my needs better than other options I looked at, and I looked at many. My needs are based upon my age, the fact that I have two completely blown discs in my lower back, I was a good bit overweight when I came back to road cycling, lack of flexibility, lack of core strength, etc.. 

As my physical condition has changed quite a bit over the past year, all for the good, I might just consider something different in the near future. If I do it too will be carbon. But before that happens, I want to go a bit further on myself.


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## tvad (Aug 31, 2003)

Why a carbon frame versus a lightweight steel frame with custom geometry to suit you?


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## ibericb (Oct 28, 2014)

tvad said:


> Why a carbon frame versus a lightweight steel frame with custom geometry to suit you?


Why not carbon, and a stock production frame of the right geometry? 

I like carbon composites as a bicycle frame material for a number of reasons. Much of that is owing to my background in advanced materials development. Second, I wasn't about to go into the waters of custom after a long stay away from road cycling. Now I less see the need, or advantage, for me. The only attraction for me is the cool factor. There are plenty of suitable options in stock production bikes that will work quite well. Third, living on the Gulf coast I really don't want the worries or bother of steel and corrosion. Everything ferrous down here either rusts, or requires persistent attention to mitigate corrosion. No thanks.


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## robt57 (Jul 23, 2011)

ibericb said:


> Everything ferrous down here either rusts, or requires persistent attention to mitigate corrosion. No thanks.


Is Reynolds 953 ferrous? And then there is Ti which is great for corrosive and wintery environments, and both common for customs. I have some of all materials, but more of steel than anything else. I would not be too concerned about rust or salt with a powder coated frame personally and empirically. Offering data points and not trying to convince anyone.

And of course if one has zero fit compromise with an off the peg offering, custom perhaps is an extravagance more than a necessity. Not that any cyclists choose bike being extravagant or anything. 

Again; just me and my personal choices, and perhaps a component of age as suggested my being 58. I sold 2 carbon bikes and gained two steel this season. And, I was in the front 3 positions mostly for a 35 mile group ride on a 90s 753 Steel custom for yesterdays jaunt FWIW. And I still do have a Scott Addict, my last all carbon bike. Stiffness I used to perceive as needed has changed for me. My thighs are not near the 28" they once were 15-8 years back. I used to perceive flex in frames more back then.


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## ibericb (Oct 28, 2014)

robt57 said:


> Again; just me and my personal choices, ....


and that's the key point.


There are many options. I'm pleased with mine, for now at least. It meets my needs quite well. There are others I would love to try. Maybe someday (if I live long enough) I'll end up liking something else better. It's a journey, not a destination.

FWIW there are a number of custom steel and stainless steel bikes I have drooled over for what to me is their coolness factor, and the nostalgic throwback of having grown up on steel frame bikes. But at this point in my life I have priorities which overrule cool and nostalgia.


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## Jwiffle (Mar 18, 2005)

The one argument I don't get from the stiffer means more power crowd is the assertion that manufacturers wouldn't make stiffer frames if it weren't true.

As has been pointed out, stiffer frames do have some benefits, just not necessarily regarding power transfer. But marketing departments will use ANYTHING to bolster sales, even if it's a lie. Think it was Zinn who one mentioned he was at the wind tunnel years ago when Camelbak was doing some testing. Results showed a hydration pack was definitely slower than bottles. Yet, a couple of weeks later he was reading ads from Camelbak stating their packs were more aero and faster than bottles! Turned out during the 5 seconds one is drinking from a bottle with their elbow in the air, they were less aero than those same 5 seconds if drinking from a pack. So 3-4 drinks in an hour meant you would be more aero for about 30 seconds than if you used bottles. 59.5 minutes more aero with bottles, 0.5 minutes more aero with a pack, but Camelbak of course only focused on the 0.5 minutes to make their product look good. So just because manufacturers like to point out their frames are stiffer than the competition doesn't necessarily equate to faster than the competition, even though they're trying to lead you into thinking that.

Furthermore, as Pirx said in his very first post, recent bikes are so close in terms of stiffness that it doesn't make a difference in power transfer. I assume, maybe I'm wrong, that my 6-7 year old steel bike is less stiff than my new carbon wonder that is touted for its stiffness. If it is, I can't feel it. What I do know is my steel bike is slower. What I can feel is that it's 10 pounds heavier. The new bike is also more aero (at least according to the manufacturer, as it's an aero bike. Again, must take that claim even with a little salt, as frame's aero properties are dwarfed by the rider's lack of aero properties.) All of my bikes over the last 10 years have been stiff enough for me not to be able to actually discern flex. Have been able to discern it on some really old bikes, but I could still make them go.


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## gaff (Jun 9, 2014)

......


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## gaff (Jun 9, 2014)

Pirx said:


> If some of the energy input by the rider is used to temporarily flex the frame, once the frame un-flexes the energy is returned. All of it. No energy is lost. None. At. All.


_this is a response to a page 1 OP Post

_In the above case the returned energy from the unflexing frame is returned to the rider (lets call this resistive feedback). Indeed "no energy is lost" but the energy that is returned results in the rider having to expend greater force for the same result due to the resistive feedback. A stiffer frame would return less energy to(wards) the rider via unflexing. This is not to say wether this variation in resistive feedback is significant, or that some riders might perform better on a more 'lively' frame.


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## aclinjury (Sep 12, 2011)

Jwiffle said:


> The one argument I don't get from the stiffer means more power crowd is the assertion that manufacturers wouldn't make stiffer frames if it weren't true.
> 
> As has been pointed out, stiffer frames do have some benefits, just not necessarily regarding power transfer. But marketing departments will use ANYTHING to bolster sales, even if it's a lie. Think it was Zinn who one mentioned he was at the wind tunnel years ago when Camelbak was doing some testing. Results showed a hydration pack was definitely slower than bottles. Yet, a couple of weeks later he was reading ads from Camelbak stating their packs were more aero and faster than bottles! Turned out during the 5 seconds one is drinking from a bottle with their elbow in the air, they were less aero than those same 5 seconds if drinking from a pack. So 3-4 drinks in an hour meant you would be more aero for about 30 seconds than if you used bottles. 59.5 minutes more aero with bottles, 0.5 minutes more aero with a pack, but Camelbak of course only focused on the 0.5 minutes to make their product look good. So just because manufacturers like to point out their frames are stiffer than the competition doesn't necessarily equate to faster than the competition, even though they're trying to lead you into thinking that.
> 
> Furthermore, as Pirx said in his very first post, recent bikes are so close in terms of stiffness that it doesn't make a difference in power transfer. I assume, maybe I'm wrong, that my 6-7 year old steel bike is less stiff than my new carbon wonder that is touted for its stiffness. If it is, I can't feel it. What I do know is my steel bike is slower. What I can feel is that it's 10 pounds heavier. The new bike is also more aero (at least according to the manufacturer, as it's an aero bike. Again, must take that claim even with a little salt, as frame's aero properties are dwarfed by the rider's lack of aero properties.) All of my bikes over the last 10 years have been stiff enough for me not to be able to actually discern flex. Have been able to discern it on some really old bikes, but I could still make them go.



I have a few bikes of varying levels of stiffness. One bike an aluminum crit-like bike (stiffest), one bike a pure carbon (pretty stiff), one bike a stainless steel (stiff but heavy), one bike a titanium (oh, people would say noodle). I have put all 4 bikes on the trainer, with rear axel locked down, and when I attempt to perform a 10-second ALL OUT seated power sprints, and had my sister video tape the lateral movement of the bottom brackets, well I could clearly see that the titanium bike had a visibly greater lateral movement in its bottobom bracket area compared to the aluminum bike. I was for sure saying to myself, ok the ti bike flexed too much, therefore it must be the slowest of the bunch. Conventional thinking right? But on the road (flat road), I'm every bit as fast in a STEADY-STATE but high intensity (well above FTP, but not an all-out sprint) on the ti bike versus all the other bikes. It is only when it an ALL OUT sprint that the ti bike loses, and it loses because the flex in its frame comes to affect its handling characteristic and thus I cannot control it as well as the other bike, and when you have less control on the bike you can't continue to sprint because you have no confidence. 

So if anything, if we were to emphasize about stiffness, it should be about how stiffness affect the control of the bike in an all out sprint (or in a wicked fast descent). Energy transfer? Not so much, and reasons already been well laid out by Pirx and Iberic in here.


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## Jwiffle (Mar 18, 2005)

aclinjury said:


> I have a few bikes of varying levels of stiffness. One bike an aluminum crit-like bike (stiffest), one bike a pure carbon (pretty stiff), one bike a stainless steel (stiff but heavy), one bike a titanium (oh, people would say noodle). I have put all 4 bikes on the trainer, with rear axel locked down, and when I attempt to perform a 10-second ALL OUT seated power sprints, and had my sister video tape the lateral movement of the bottom brackets, well I could clearly see that the titanium bike had a visibly greater lateral movement in its bottobom bracket area compared to the aluminum bike. I was for sure saying to myself, ok the ti bike flexed too much, therefore it must be the slowest of the bunch. Conventional thinking right? But on the road (flat road), I'm every bit as fast in a STEADY-STATE but high intensity (well above FTP, but not an all-out sprint) on the ti bike versus all the other bikes. It is only when it an ALL OUT sprint that the ti bike loses, and it loses because the flex in its frame comes to affect its handling characteristic and thus I cannot control it as well as the other bike, and when you have less control on the bike you can't continue to sprint because you have no confidence.
> 
> So if anything, if we were to emphasize about stiffness, it should be about how stiffness affect the control of the bike in an all out sprint (or in a wicked fast descent). Energy transfer? Not so much, and reasons already been well laid out by Pirx and Iberic in here.


I would hazard a guess that the stiffness problem with the ti bike is relative to the head tube, rather than the bb. A stiffer front end might help with control of the bike in a sprint effort.


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## tvad (Aug 31, 2003)

ibericb said:


> I like carbon composites as a bicycle frame material for a number of reasons. Much of that is owing to my background in advanced materials development.


What are those reasons specifically



ibericb said:


> ...living on the Gulf coast I really don't want the worries or bother of steel and corrosion. Everything ferrous down here either rusts, or requires persistent attention to mitigate corrosion.


Practical.


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## ibericb (Oct 28, 2014)

tvad said:


> What are those reasons specifically


At the top of the list, strength:weight, durability / fatigue resistance , and corrosion resistance. After that it gets really subjective.


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## myhui (Aug 11, 2012)

But a stiff frame accelerates faster when measured within 90 degrees of chainring rotation.

I'm staying with my stiff frame, so I never need to go cry with my mom and tell her "my bicycle frame is too soft, mom."


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## Pirx (Aug 9, 2009)

gaff said:


> In the above case the returned energy from the unflexing frame is returned to the rider (lets call this resistive feedback). Indeed "no energy is lost" but the energy that is returned results in the rider having to expend greater force for the same result due to the resistive feedback.


No, this is not correct, and has been addressed before. You'll need to read more than just my first post to weigh in on this debate.


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## Jackhammer (Sep 23, 2014)

velodog said:


> I don't understand the anger that seems to be coming from the stiffer is better crowd, all the while professing that we should ride what we want. No one ever said anything different, just that much of the stiffness claim is marketing, so why all the emotion?
> 
> It seems like someone needs to get together a crank based power meter and a wheel based unit and compare wattages from one end to the other on a good plastic bike, and then on a good steel bike, and compare apples to apples.
> 
> ...





Pirx said:


> Thanks very much for restating the point of all this.
> 
> And, yes, I'm really starting to become more interested in those fascinating strong emotions that people bring to this debate, which clearly cloud their understanding of what is being said. Where do those feelings come from? Is it something as simple as "Now that I've spent five grand on that brand new 2015 frame that's "30% stiffer in the bottom bracket" than my old one, this guy comes along and says it won't make me any faster, so I wasted all this money"? Actually, I doubt that it's that, but what is it, then?


“Shallow ideas can be assimilated; ideas that require people to reorganize their picture of the world provoke hostility.” 
― James Gleick, _Chaos: Making a New Science_


“quoting Tolstoy: “I know that most men, including those at ease with problems of the greatest complexity, can seldom accept even the simplest and most obvious truth if it be such as would oblige them to admit the falsity of conclusions which they have delighted in explaining to colleagues, which they have proudly taught to others, and which they have woven, thread by thread, into the fabric of their lives.” 
― James Gleick, _Chaos: Making a New Science 

_Great title to thread!

Mommy, please tell me another story....LOL


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## tvad (Aug 31, 2003)

ibericb said:


> At the top of the list, strength:weight, durability / fatigue resistance , and corrosion resistance. After that it gets really subjective.


Very practical. Definitely don't want to open the Pandora's box of subjectivity. 

Thanks.


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## Pirx (Aug 9, 2009)

Jackhammer said:


> Mommy, please tell me another story....LOL


Yeah, but then you have this:

Little girl: "[Sobbing...] Mommy, mommy, Pirx is being mean to me! He says my new shiny red bike is ugly! [Sniffle, sob...]"

Pirx: "[Patting her head] Now now, don't be sad, I never said your new shiny red bike is ugly. It's really quite pretty, and it goes so well with your little red tutu!"

Little girl: "[Sniffle...]"

Pirx: "All I was saying was that the shiny blue bicycle we bought your brother last year is just as pretty."

Little girl: "[Wailing...] Mom! Pirx is being mean to me! ..."


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## robt57 (Jul 23, 2011)

ibericb said:


> It's a journey, not a destination.


Ahhh, but what will the average speed be for the journey, 14MPH or 22MPH ?? 




> But at this point in my life I have priorities which overrule cool and nostalgia.



I hate how life gets in the fooking way!


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## tvad (Aug 31, 2003)

Pirx, what criteria weighed in your decision to purchase a carbon Felt F1 versus a frame made of different material?


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## myhui (Aug 11, 2012)

Advertising?


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## ibericb (Oct 28, 2014)

tvad said:


> Very practical. Definitely don't want to open the Pandora's box of subjectivity.
> 
> Thanks.


NP. However, none of those draw on the real strength of carbon fiber composites as engineering materials. The real attribute is the ability to design the properties for the application. That is, to put material where it's needed, for its intended purpose. That leads into a lot of subjective qualities that come with the use (eg, shape, feel, ...). The key to success becomes the quality of the engineering and design. That is the Pandora's box of carbon composites.


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## ibericb (Oct 28, 2014)

Pirx said:


> ...
> Little girl: "[Wailing...] Mom! Pirx is being mean to me! ..."


Oh, just take her lollipop and be done with it.


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## goodboyr (Apr 19, 2006)

This crap begs for moderation.


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## robt57 (Jul 23, 2011)

goodboyr said:


> This crap begs for moderation.



Could you be more specific, there is quite a bit of feces in this thread...

Not the least of which is this post I typed. ;O


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## goodboyr (Apr 19, 2006)

It's the pirx and ibericb stuff offensive to women.


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## Pirx (Aug 9, 2009)

tvad said:


> Prix, what criteria weighed in your decision to purchase a carbon Felt F1 versus a frame made of different material?


Pirx, you mean? :thumbsup:

It was weight, stiffness [gasp!], and expected durability, first and foremost, plus I liked the aesthetics. Subjective features are quite important in my opinion, given that objectively speaking, the differences between different brands and models of frames are minimal.

For the stiffness, by the way, and to get away from the performance discussion for a bit, while my steel bike (1980s Basso Loto) rides beautifully under most circumstances, it does exhibit a bit of high-speed wobble beyond about 40 mph, which can be a tad unnerving on fast descents. The carbon bike runs as if on rails at any speed, in contrast. I know that stiffness is only a part of that story, too, but it does make for more confident descents.


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## Pirx (Aug 9, 2009)

goodboyr said:


> It's the pirx and ibericb stuff offensive to women.


I'm sure you jest, right? 

Well, as a matter of fact, I fear you're serious. Crying for a mod every time your gentle sensitivities are being triggered 

For the record, there is not and never has been anything posted that a mentally sane person could offensive to any gender, nor was there ever any intention by anybody in this direction.


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## goodboyr (Apr 19, 2006)

It's the forum rules, stupid.


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## robt57 (Jul 23, 2011)

Pirx said:


> Pirx, you mean? :thumbsup:
> 
> It was weight, stiffness [gasp!], and expected durability, first and foremost, plus I liked the aesthetics.


Did you at least think of using the words 'Yet Compliant' in that post?


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## Pirx (Aug 9, 2009)

goodboyr said:


> It's the forum rules, stupid.


Would you like to point out the specific rule(s) you have in mind? Do you think you may have violated any of those rules, in your own narrow interpretation, with that last epithet of yours? Inquiring minds want to know... :aureola:


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## Pirx (Aug 9, 2009)

robt57 said:


> Did you at least think of using the words 'Yet Compliant' in that post?


Absolutely, but I could contain myself, barely.


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## tvad (Aug 31, 2003)

Pirx said:


> Pirx, you mean? :thumbsup:


Rats. Darned autocorrect. I need to teach the dictionary to ignore Pirx.



Pirx said:


> It was weight, stiffness [gasp!], and expected durability, first and foremost, plus I liked the aesthetics.
> 
> For the stiffness, by the way, and to get away from the performance discussion for a bit, while my steel bike (1980s Basso Loto) rides beautifully under most circumstances, it does exhibit a bit of high-speed wobble beyond about 40 mph, which can be a tad unnerving on fast descents. The carbon bike runs as if on rails at any speed, in contrast. I know that stiffness is only a part of that story, too, but it does make for more confident descents.


Interesting. 

You don't consider improved descending of your carbon Felt F1 a performance aspect of the frame?


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## Pirx (Aug 9, 2009)

tvad said:


> You don't consider improved descending of your carbon Felt F1 a performance aspect of the frame?


Hmm, you have a point. I think you are right that this could and probably should be considered a "performance feature". So, let me rephrase what I said; it should have read "and to get away from the power efficiency discussion...".

So, yes, absolutely, there can be very good reasons to prefer a laterally stiff frame over a more compliant one; as I have said multiple times in this thread. It's just that power efficiency isn't one of them, as far as we know.


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## goodboyr (Apr 19, 2006)

Pirx said:


> Would you like to point out the specific rule(s) you have in mind? Do you think you may have violated any of those rules, in your own narrow interpretation, with that last epithet of yours? Inquiring minds want to know... :aureola:


Here's a copy, for your reference. 

*ConsumerREVIEW.com strives to provide a product research resource and Web community of the highest quality and integrity. We encourage open, honest and respectful communication between all of our members. Our community guidelines are based upon these basic values: 
We believe everyone has something to contribute 
We believe that an open, honest and respectful environment can generate stimulating discussion and valuable contributions from all of our members 
A healthy community has room for and encourages participation from everyone, regardless of their age, background or level of expertise 
We do not and cannot review all content posted by viewers on the Web site, and we are not responsible for such content. However, we do reserve the right to delete or edit any reviews or other postings that are not, in our sole discretion, in the spirit of these basic values. We will monitor posting activity of anyone who violates the following guidelines and, if necessary, restrict their ability to post reviews or messages on the site.*


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## Pirx (Aug 9, 2009)

So, where in this material does it say anything that would imply my humorous "little girl" post? Do you believe that post would have been fine if I swapped the little girl and her brother for a little boy and his sister? If so, why do you think so, and if not, why not?

P.S.: Yes, I really want to know, since I honestly cannot fathom what your objection might be, and so far you haven't even given me a clue.


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## HFroller (Aug 10, 2014)

Pirx said:


> No, this is not correct, and has been addressed before. You'll need to read more than just my first post to weigh in on this debate.


When I returned from work, I did a few back-of-the-envelope calculations on the train. Always a hazardous enterprise, and I had only half an hour, but OK.

I treated the movement of the BB as the movement of a mass attached to a spring with modulus k ( F = -kx ) under the influence of an external force F sin (zt).
The force is delivered by the rider. T is the time. Z is the angular frequency of the force. Z is essentially a re-writing of the pedaling frequency. “Regular” frequencies are seldom used in physics. 

The idea was that the BB makes a sinusoidal movement, to a good approximation in a straight line perpendicular to the plane of the bike frame. Of course the amplitude may be very small. 
The modulus k is a measure for the stiffness of the frame. The higher k, the stiffer the frame. 
Now, the BB (the spring) has an eigenfrequency w. The natural frequency with which it vibrates if you hit it with a hammer (perpendicular to the plane of the frame) and leave it alone. 
I assumed that z/w is small, say 1/100, and neglected terms of the order (z/w)^2. Pedaling frequencies are somewhere between 1 and 2 per second, I assumed that the eigenfrequency of the BB (the spring) was around 100-200 or higher (just a guess!). (z/w)^2 would be too small to be noticeable. 
I also assumed there was no damping – perfect energy conservation in the frame, in other words. 

In this modest model, the BB is moving, and as long as it moves, it has an energy. Up to terms of the order (z/w) the average energy over a cycle turned out to be F^2 / 2k (F is the amplitude of the force). The rider has to “give” the BB some energy to keep it moving in a sinusoidal way – but this energy is constant for a constant force. Remember – I assumed there’s no damping in the frame. No energy gets lost. Once you’ve given it, no need to add more energy to the frame. You pay upfront, but you only pay once. 

But what happens if the force on the BB changes? When you sprint, or stop pedaling and get going again a few moments later? As I already mentioned, I assumed perfect energy conservation in the frame. However, this doesn’t mean the rider “gets the energy back”. The physiology of muscles doesn’t work that way. If you keep a perfect spring moving with your arm (with a frequency much lower than the eigenfrequency) there’s perfect energy conservation in the spring, but your arm will be tired after a while. 
How muscles work in the real world, I don’t know. I don’t think the frame itself can turn the movement of the BB, perpendicular to the plane of the frame, into forward propulsion. For that, you need a rider, and the combination of rider + bike is a very complicated system. 

But let’s assume for a moment that your muscles get none of the energy in the sinusoidal movement of the BB back. It stops moving when you stop pedaling, but your muscles refuse the present the BB is giving. Then the stiffness of the frame might make a difference. Then the changes in the average energy of the BB are influenced by k, the modulus of the spring (the stiffness of the frame). If k is high, there is less energy in the BB for the same force F. The changes in the average energy are smaller when F changes. Each time you sprint and change F, a stiff frame might be more efficient.

What does it all mean? I don’t know. It’s perfectly possible that bike frames have reached a point where differences in stiffness are too small to be noticed. 

I invite everyone the repeat my calculations, of course. I’ve been known to be wrong more than once in my life.


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## tvad (Aug 31, 2003)

Pirx said:


> Hmm, you have a point. I think you are right that this could and probably should be considered a "performance feature". So, let me rephrase what I said; it should have read "and to get away from the power efficiency discussion...".
> 
> So, yes, absolutely, there can be very good reasons to prefer a laterally stiff frame over a more compliant one; as I have said multiple times in this thread. It's just that power efficiency isn't one of them, as far as we know.


I own a custom geometry carbon frame (tube to tube construction with carbon wrap joinery), and will hopefully take delivery of a custom geometry True Temper S3 steel frame with carbon fork in the next few weeks. Both bikes have very similar, but not identical, geometries designed from the same fit measurements. Both bikes will have identical drive trains, seat posts, saddles and cockpits. Of course, I can interchange wheels to eliminate them as a variable. I will be interested to compare their performance on identical and familiar rides.


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## ibericb (Oct 28, 2014)

goodboyr said:


> It's the pirx and ibericb stuff offensive to women.


Please tell me, what part of what I posted is "offensive to women", and how so? Are you a woman?


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## Pirx (Aug 9, 2009)

HFroller said:


> The idea was that the BB makes a sinusoidal movement, to a good approximation in a straight line perpendicular to the plane of the bike frame.


I think that assumption is problematic. If true, then the motion of the BB would have almost no energy implications for the rider, since the motion of the BB is orthogonal to the pedal motion, so there's no exchange of energy. Practically speaking, I think a more realistic model is one where an important component of the BB motion is a rotation around a longitudinal axis (relative to the bike), which leads to vertical displacement (in line with the pedal motion) during various phases of the pedaling cycle. There's some material on this in some of the references that have been cited in this thread.



HFroller said:


> I assumed that z/w is small, say 1/100, and neglected terms of the order (z/w)^2. Pedaling frequencies are somewhere between 1 and 2 per second, I assumed that the eigenfrequency of the BB (the spring) was around 100-200 or higher (just a guess!). (z/w)^2 would be too small to be noticeable.


Yes, that's all fine; like I had said earlier in a response to you, we don't need to worry about resonances, even though your ratio may be a bit on the high side, but I'm not sure, and the exact numbers don't matter much.



HFroller said:


> In this modest model, the BB is moving, and as long as it moves, it has an energy.


Yes. Essentially, you end up investing the energy coming from the flex achieved during one downstroke. There was an estimate of that somewhere in the thread, which was of the order of 4% of the energy in one full downstroke, for a very high estimate. Like you say, after that initial investment, no further energy is deposited in the frame oscillation.



HFroller said:


> In this modest model, the BB is moving, and as long as it moves, it has an energy. Up to terms of the order (z/w) the average energy over a cycle turned out to be F^2 / 2k (F is the amplitude of the force).


Yep, that looks about right, see above for an estimate of the actual number.



HFroller said:


> I invite everyone the repeat my calculations, of course. I’ve been known to be wrong more than once in my life.


I think the handiwork is fine, but just like with PDEs, it's all in the boundary conditions, or assumptions, in your case.


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## ibericb (Oct 28, 2014)

tvad said:


> I own a custom geometry carbon frame (tube to tube construction with carbon wrap joinery), and will hopefully take delivery of a custom geometry True Temper S3 steel frame with carbon fork in the next few weeks. Both bikes have very similar, but not identical, geometries designed from the same fit measurements. Both bikes will have identical drive trains, seat posts, saddles and cockpits. Of course, I can interchange wheels to eliminate them as a variable. I will be interested to compare their performance on identical and familiar rides.


Sounds very cool. I look forward to hearing about your comparisons, good, bad and ugly.

Curious - do you typically use a power meter?


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## Pirx (Aug 9, 2009)

tvad said:


> I will be interested to compare their performance on identical and familiar rides.


So will be all of us, that will indeed be interesting. Of course, ideally you would have to do a blind test, with somebody somehow masking the two frames so you wouldn't know which one you're riding.  Just kidding, I'm genuinely interested in your report.


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## ibericb (Oct 28, 2014)

Pirx said:


> ...
> I think the handiwork is fine, but just like with PDEs, it's all in the boundary conditions, or assumptions, in your case.


One detail I think that may have led to a different conclusion is the assessment of what happens in the "uncoiling" of the loaded frame spring.

There are three possibilities which have previously been noted: (1.) the uncoiling of the frame spring is translated into pedal force against the advancing force of the cyclists foot, (2) the uncoiling serves merely to reposition the rider, and (3) the potential for some elastic recovery within the human muscle system under certain conditions (eccentric contraction). I didn't see, or maybe I missed it, in HFroller's description of his 30-min quickie analysis that he really considered those as energy recovery mechanisms.


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## tvad (Aug 31, 2003)

Pirx said:


> So will be all of us, that will indeed be interesting. Of course, ideally you would have to do a blind test, with somebody somehow masking the two frames so you wouldn't know which one you're riding.


Thank goodness. I thought I'd have to ride blindfolded.


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## Pirx (Aug 9, 2009)

ibericb said:


> There are three possibilities which have previously been noted: (1.) the uncoiling of the frame spring is translated into pedal force against the advancing force of the cyclists foot, (2) the uncoiling serves merely to reposition the rider, and (3) the potential for some elastic recovery within the human muscle system under certain conditions (eccentric contraction).


He essentially ruled out #1 and #2 by his assumptions (which is one reason why I think they're problematic), and said he didn't know enough about #3, which is fair enough; neither do you or I, I think.


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## Pirx (Aug 9, 2009)

tvad said:


> I thought I'd have to ride blindfolded.


Well, that would work, too, for a little while...


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## HFroller (Aug 10, 2014)

Pirx said:


> I think that assumption is problematic. If true, then the motion of the BB would have almost no energy implications for the rider


I forgot to add that to keep things simple I assumed that on t=0 the displacement of the BB x(t) = 0 and the velocity x'(t) = 0 too. 
However, I don't agree that my assumption is problematic. It certainly does not cover everything that's happening - how could it? - but it is part of it. I think bikes and riders are not perfect enough to exclude an exchange of energy leading to a motion of the BB perpendicular to the plane of the frame. Such perfection would assume an inflexible frame, I think - and make the discussion moot. On a more vulgar level, I can see the BB swinging form left to right when I ride the the very flexible steel frame of my partner's bike and push it a bit. 
I also calculated the amplitude of the sinusoidal movement of the BB and arrived at approximately F/k. With modern frames, this amplitude will be under 0.01 meter, giving an averaged energy in the movement of the BB of F/200 (in the appropriate metrical units). I don't make assumptions about the magnitude of F, but I wouldn't be surprised if the relevant figures turned out to be rather small in reality.


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## ibericb (Oct 28, 2014)

tvad said:


> Thank goodness. I thought I'd have to ride blindfolded.


 :idea:

I'll offer to help. You could wrap both frames in plain brown paper, then ship the to me. I'll test ride them for you, and report back which frame you would like better, and why.


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## Pirx (Aug 9, 2009)

HFroller said:


> However, I don't agree that my assumption is problematic. It certainly does not cover everything that's happening - how could it? - but it is part of it.


Oh yes, it's part of it, but in my intuition that's a less important part. The motion you assume automatically results in an induced motion of the rider's foot that is orthogonal to the main power-producing motion (downwards in a plane parallel to the plane of the frame). If we assume that the rider's center of gravity simply follows that sideways motion (fairly reasonable, I think), then there would be no way to transfer energy into the deformation you have assumed, at all. Now, I'll give you that, if I relax the additional assumptions I have now tacitly introduced such a coupling becomes possible, but the whole thing feels spurious to me. If, on the other hand, you include rotation of the bottom bracket under the off-center load from the pedal, then you'll naturally get energy transfer, and you can even induce some sideways motion.



HFroller said:


> I think bikes and riders are not perfect enough to exclude an exchange of energy leading to a motion of the BB perpendicular to the plane of the frame.


I do agree, despite what I said above.


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## ibericb (Oct 28, 2014)

Pirx said:


> He essentially ruled out #1 and #2 by his assumptions (which is one reason why I think they're problematic),


We agree, and that's why I raised it. I did so only because of its significance in the discussion. It's getting easy to get lost in this thread.



> ... he didn't know enough about #3, which is fair enough; neither do you or I, I think.


Nope, not me. But I find the possibility very intriguing from a biomechanical viewpoint.


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## Pirx (Aug 9, 2009)

ibericb said:


> :idea:
> 
> I'll offer to help. You could wrap both frames in plain brown paper, then ship the to me. I'll test ride them for you, and report back which frame you would like better, and why.


So you'll send him back a report, but you somehow forgot the part about shipping the bikes back to him, eh? Smooth... :devil:


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## velodog (Sep 26, 2007)

goodboyr said:


> It's the forum rules, stupid.


Which part of calling somebody stupid is "respectful communication", per the rules?


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## ibericb (Oct 28, 2014)

Pirx said:


> So you'll send him back a report, but you somehow forgot the part about shipping the bikes back to him, eh? Smooth... :devil:


Who me? I will surely return his bikes -- when all testing has been completed.


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## BikeLayne (Apr 4, 2014)

In the 70's I rode an Eisentraut touring bike and the bottom bracket was quite flexible however I could keep up with a group. Then in 82 I bought an Allez and it was much stiffer in that area but I did not really see an increase in speed. Nothing to monitor it with back then except the clock on the stove. I seem to remember I could do the usual loop of 20 miles in an hour with about 50fpm of climbing. I rode that bike for 30 years give or take. Now I have a Lighthouse and it is stiffer yet. I am unable to realize any flex in the bottom bracket area with Columbus Spirit tubing however I am much slower these days at 68y/o. I have ridden 3600 miles so far this year. I cannot keep up with the kids on the weekly shop rides but I turn out once in a while anyway. They stop to regroup once in a while so it makes it possible. Back in the day with the Santa Cruz Cycling club (70's) they did not stop to regroup so if you were dropped you just went on your own ride because they were gone.


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## tvad (Aug 31, 2003)

ibericb said:


> Curious - do you typically use a power meter?


I do, but it's crank based, and I don't presently plan to install magnet sensors on the second bike. The cranks can be swapped in about 15 minutes.

My wheel based PowerTap was recently sold. That would have been the easiest.

Since both frames are custom geometry built to my long legged, short torso'd, long armed freakish body, the bikes would not likely fit others.


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## ibericb (Oct 28, 2014)

The reason I ask about the power meter is I am really curious about the potential biophysical effect of frame stiffness, or frame response, on a cyclist's ability to develop power. This follows along the line of Hene's explanation of the power differences they noted between the frames they tested. One of the comparative tests you might consider is something similar, where you black out the power meter, then push a sustained hard effort based on perceived effort, like a hill climb, and then see what the power meter says after the fact.


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## tvad (Aug 31, 2003)

^On other hand, I would be inclined to produce a similar effort based on wattage (say a sustained 250 watt effort) over the same road and distance, and see how the speeds differ from bike to bike (keeping in mind the same group sets, gearing, saddles, cockpit, wheels and pedals). I might wear a different blindfold.


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## ibericb (Oct 28, 2014)

tvad said:


> ^On other hand, I would be inclined to produce a similar effort based on wattage (say a sustained 250 watt effort) over the same road ans distance, and see how the speeds differ from bike to bike (keeping in mind the same group sets, gearing, saddles, cockpit, wheels
> and pedals). I might wear a different blindfold.


You just need to account for any aero differences.


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## tvad (Aug 31, 2003)

ibericb said:


> You just need to account for any aero differences.


I think it's negligible. The carbon tubing is not aero...essentially round. If anything the steel tubing will have a smaller profile. On a climb aero won't matter anyway.


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## duriel (Oct 10, 2013)

This is getting good.... geeks met the real world.... say hello!


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## HFroller (Aug 10, 2014)

Pirx said:


> Oh yes, it's part of it, but in my intuition that's a less important part.


That's where our intuitions disagree .

I suggested that the rider doesn't have to add more energy once he got this (supposedly) sideways movement of the BB going. Now I'm not so sure anymore. 

Yesterday I looked at the average energy in the BB over a cycle, which is a constant. But today I looked at the changes of the energy. Half of the time they are positive (the rider adds energy), the other half of the time negative. I think we agree that the rider doesn't get all his energy back during the negative half of the cycle, because of physiology etc. But this means that to keep the movement going, the rider adds some energy during each cycle. 

The energy he adds to the movement of the BB is inversely proportional to k, the stiffness of the spring (the frame). This suggests that – in my model, theoretically etc. – stiffer frames are more efficient – even when the applied force Fsin(zt) does not change. The stiffness plays a role even when the rider is not accelerating, sprinting etc. 

The question is how much difference it makes in the real world. I don't know. I don't even know what it means when manufacturer X claims that the BB of a new bike is "Y% stiffer". 

Side note: you're right that the assumption that z/w is small is rather obvious, but I wanted to know what it means physically. My calculations suggest that it means that we can neglect the kinetic energy of the sideways movement of the BB – only the potential energy is relevant. This explains why the energy of the spring (the BB) is not constant, but changes over a cycle (although the average is a constant). This is a big difference with a spring that oscillates with its eigenfrequency. In that situation, the total energy of the spring (potential + kinetic energy) is a constant all the time.

And again, I invite everyone to repeat my calculations. It's always possible I made a mistake or didn't interpret the results correctly.


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## ibericb (Oct 28, 2014)

tvad said:


> I think it's negligible. The carbon tubing is not aero...essentially round. If anything the steel tubing will have a smaller profile. On a climb aero won't matter anyway.


I'm not sure what a difference in speed at a given indicated crank power output is telling you as there are a number of power consumption losses other than changes in kinetic and potential energy (aero, rolling resistance, frictional losses, and drivetrain losses). In your case with the same wheels and tires at the same inflation frictional losses and rolling resistance should essentially be the same. That leaves aero and drivetrain loss differences, both of which I would guess would be greater than differences in any frame energy losses.

I was thinking in your case it will be more about your small positional differences, and drag details for things like cables, bars, etc. Even on a climb that counts too. It's one of the reasons Team Sky trains and prefers seated climbing to the max extent possible. It's also probably a greater difference than any frame energy losses. Either way, speed at a given power level doesn't address the biophysical effects on a cyclist's ability to develop power I was raising.  It's an interesting hypothesis from Heine. I'd just like to see a lot more testing than the limited dataset he provides.


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## tvad (Aug 31, 2003)

^I'm just going to enjoy riding the bikes and leave the analysis alone.


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## ibericb (Oct 28, 2014)

tvad said:


> ^I'm just going to enjoy riding the bikes and leave the analysis alone.


But, but ....


A very good idea!

:thumbsup:


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## Pirx (Aug 9, 2009)

HFroller said:


> That's where our intuitions disagree .
> 
> I suggested that the rider doesn't have to add more energy once he got this (supposedly) sideways movement of the BB going.



Well, I thought about your model on my commute home yesterday, and I can offer a more succinct criticism. I think the model you are using is fundamentally flawed, because you have baked an artificial asymmetry into your assumptions that biases your results. 


On the input side, you assume that _somehow_ the rider will add energy to the sideways motion of your BB, even though there's no obvious way for this to happen (under the assumption of BB oscillation normal to the plane of the frame, and pedal motion parallel to that same plane). By itself that's still fine; it's a rough conceptual model after all, and you somehow need to get energy into that BB motion, otherwise there would be no motion at all. 
However, the problem now is that, on the output side, you claim that, because of that same specific motion of the BB that you assume, there's no way for energy to be converted into propulsion, leaving as the only way to get energy out of the frame flex the rider itself.


Clearly, (1) is inconsistent with (2). Certainly, there's ways to give vague justifications for both, but the fact remains that with this combination of assumptions you have predetermined the outcome. Reminding ourselves that we are dealing with small effects either way, a model like this cannot be trusted.

Bottom line for me is, there's a reason why I am sticking to those global energy conservation arguments. If you want to go beyond those, I do not think there is any way to avoid a very detailed simulation if you want to arrive at a definite result. Or, of course, a well-executed experiment, ideally.


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## duriel (Oct 10, 2013)

Are they bringing back Monty Python to illustrate this discussion?

I think you guys nailed it!


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## Nereth (Oct 7, 2015)

So, I skipped ahead a bit after seeing the argument going around in circles.

It's true that barring hysteresis losses in the frame there wouldn't be much mechanism for frame deflection to directly impact efficiency.

But this problem isn't as simple as just a deflecting frame. Some examples:

1) Chain line - poor chain line has been shown to have some impact on efficiency. My understanding is that it is a very small impact. But non-zero. In any case, you will be pushing the chain line about (for better or worse) during every pedal stroke.

2) The human body is most certainly *not* frictionless. If the frame is flexing and recovering on every pedal stroke, then depending on where in the pedal stroke the flexure and recovery happens (depends on the rider), it is possible that you will have to make longer pedal strokes. The pedal strokes are at lower average force, so that's theoretically no issue - but you do open a whole biomechanical can of worms - it's hard to say what crank length is optimal for a rider, and it's similarly even harder to say if this is detrimental or beneficial. But it's another effect.

3) Then there are the opposite effects. I would guess that there is less hysteresis in a frame than there likely is in the fairly putty-like human body. A flexy frame protecting your posterior from deformation over lumpy terrain will likely save some hysteresis losses.

You could likely spit out second, third, fourth order effects like this all day. None of them are likely to be large effects in the majority of cases (combined, they may become noticeable in some cases). But saying "there is absolutely no effect, you're all imagining it" because "physics says so" is a bit rich in a situation where physics has mechanisms by which there *can* be effects.

But enough of that, let's all make some more ad-hominem attacks and appeals to authority! It's much more fun that way!


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## HFroller (Aug 10, 2014)

Pirx said:


> Well, I thought about your model on my commute home yesterday, and I can offer a more succinct criticism. I think the model you are using is fundamentally flawed, because you have baked an artificial asymmetry into your assumptions that biases your results.
> (...)
> Bottom line for me is, there's a reason why I am sticking to those global energy conservation arguments. If you want to go beyond those, I do not think there is any way to avoid a very detailed simulation if you want to arrive at a definite result. Or, of course, a well-executed experiment, ideally.


The model is an oversimplification, but it's not fundamentally flawed in the way you suggest. There are no contradictions and there are no hidden assumptions. 

I assume a sideways motion of the BB and approximate it as a motion perpendicular to the plane of the frame. The approximation is not perfect, but it will do – if there is such a motion. The model assumes it's there. If you can't observe it, the model is useless. A relatively simple experiment should determine the answer. 

Once one agrees the effect is there, the cause is interesting but the detailed mechanics are not important for my analysis and that's why I don't look for causes. I do assume however that the BB wouldn't move sideways if no force were applied to it. I assume a periodic force to keep things mathematically manageable and because the force must be a consequence of the periodic pedaling force of the rider. But how exactly the combination of rider + bike makes the BB move – I don't have to know. 

I assume that the frame itself does not convert the sideways motion of the BB into forward propulsion. It's hard to see how a frame could do that. But again a relatively simple experiment should clarify things. Push sideways on the BB. Does the bike go forward? 

I make the approximation that the angular frequency of the force is much lower than the eigenfrequency of the sideways movement of the BB. Calculations suggest then that the energy of the BB is continually changing (although the average over a cycle is a constant). Does that mean there is no energy conservation in the BB? Of course not. Take a very stiff spring and make it oscillate very slowly with your hand. Assume that there's no damping in the spring – perfect energy conservation. Even then the energy in the spring continually changes, because the potential energy continually changes and because the potential energy is much, much higher than the kinetic energy – it dominates the total energy. 

However, even with a perfect spring your arm will be tired after a while. And that's exactly what – theoretically, in my model – happens when the rider makes the BB move (although I'll gladly admit that I don't know how large this effect is). 

There are no contradiction in this approach. I can't explain the reason why there is a sideways force on the BB, but I don't have to. The lack of explanation does not create an internal contradiction.

BTW: I really don't understand why you insist on general conservation of energy arguments. One cannot apply them to the frame (or the bike) alone, because the frame is not a closed system when there's a rider sitting on it an riding it. Not even approximately.


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## Pirx (Aug 9, 2009)

duriel said:


> Are they bringing back Monty Python to illustrate this discussion?


Certainly, this thread had its comical moments, such as this post, but apart from such aberrations, many of the contributions here have been quite serious. You may have missed those, somehow.



Nereth said:


> So, I skipped ahead a bit after seeing the argument going around in circles.


It would appear you missed quite a bit when doing so.



Nereth said:


> 1) Chain line - poor chain line has been shown to have some impact on efficiency. My understanding is that it is a very small impact.


Yes. Now look at the gap between your chain and derailleur cage, and keep in mind that, at the very most, some people experience chain rubbing under frame flex. My guess is most don't, however. Thus the change in change line due to frame flex is very small, and given that the effects of even significant changes of the chain line (at extreme ends of the cassette) are also small, we can safely neglect this effect.



Nereth said:


> 2) The human body is most certainly *not* frictionless.


This has been discussed in very great detail. The result is that the effect of frame flex on bio-mechanical efficiency is entirely unclear. I note in passing, as has been discussed also, that studies on the effect of crank length on biomechanical efficiency have been done. In one such study no significant effects were found even for extreme variations of crank length between 145mm up to 195mm crank lengths. See this article for one example.



> 3) Then there are the opposite effects. I would guess that there is less hysteresis in a frame than there likely is in the fairly putty-like human body. A flexy frame protecting your posterior from deformation over lumpy terrain will likely save some hysteresis losses.


Interesting point, yes.



> saying "there is absolutely no effect, you're all imagining it" because "physics says so" is a bit rich in a situation where physics has mechanisms by which there *can* be effects.


This is not an accurate representation of the argument that has been put forward by me, as you would know if you had read the pertinent posts in this thread.



> But enough of that, let's all make some more ad-hominem attacks and appeals to authority! It's much more fun that way!


Likewise, I do not think this is a fair characterization of this thread as a whole. I will note that I find it somewhat inappropriate to see such a characterization coming from someone who admittedly has skipped much of the discussion. No matter, yes, while it is true that this thread has seen its share of nonsense (see above), if you do read through the wealth of the material that has been posted, including more advanced matter that has been referenced and linked to, you may find that there is indeed some material of higher-than-average quality in this thread. I encourage you to read it, if you are interested.


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## duriel (Oct 10, 2013)

Nereth said:


> ad-hominem attacks


I don't see much of that here. Actually I am starting to sway to in agreement with the proposition, but don't tell anyone.


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## Pirx (Aug 9, 2009)

HFroller said:


> The model is an oversimplification, but it's not fundamentally flawed in the way you suggest. There are no contradictions and there are no hidden assumptions.


I'll get back to this later (well, I do have a daytime job...), but just to make sure there's no misunderstanding, no, I agree there's no contradictions per se, and you certainly have described all of your assumptions in significant detail. However, I contend that your model is not a good representation of the first-order mechanics of the system. I'll have to get back to this later, however.


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## Nereth (Oct 7, 2015)

Pirx said:


> It would appear you missed quite a bit when doing so.


I wouldn't say I skipped the majority of the thread so much as I started just scanning rapidly and noted new information became sparser and sparser.




Pirx said:


> Yes. Now look at the gap between your chain and derailleur cage, and keep in mind that, at the very most, some people experience chain rubbing under frame flex. My guess is most don't, however. Thus the change in change line due to frame flex is very small, and given that the effects of even significant changes of the chain line (at extreme ends of the cassette) are also small, we can safely neglect this effect.


My chain doesn't rub until I'm about 3/4 over on the cassette. So I'd say if people hear chain rubbing it may not be a minor amount of misalignment.

Keep in mind we are in an industry where 0.5% change in efficiency would be huge. That's saving a few watts. Saving a single watt is not insignificant when you are pushing the limit. Writing things off as 'small enough to be negligible' should be done with great care. Without characterizing how large chainline losses are, I'm not sure I would agree with you that they don't matter. There is a paper that addresses it but I didn't feel like spending money, so personally I'm not sure, but it did say it was measurable (but yes, extremely small)






Pirx said:


> This has been discussed in very great detail. The result is that the effect of frame flex on bio-mechanical efficiency is entirely unclear. I note in passing, as has been discussed also, that studies on the effect of crank length on biomechanical efficiency have been done. In one such study no significant effects were found even for extreme variations of crank length between 145mm up to 195mm crank lengths. See this article for one example.


Unclear, I would agree. But that leaves the door open for it to be, again, non-zero. Which again leaves the door open for people saying "My stiff frame feels faster" to not be guaranteed to be wrong.






Pirx said:


> Interesting point, yes.


Why thankyou.






Pirx said:


> This is not an accurate representation of the argument that has been put forward by me, as you would know if you had read the pertinent posts in this thread.


Frankly I haven't even paid too much attention to the names behind the posts, so I may not even be pointing the finger at you. I don't know anyone here. I just saw people on each side saying either "I can feel it so it's there" or "Physics says it's not there so it's not". The first argument is dodgy for obvious reasons, the second argument is dodgy in a world where we can start listing out non-zero effects.





Pirx said:


> Likewise, I do not think this is a fair characterization of this thread as a whole. I will note that I find it somewhat inappropriate to see such a characterization coming from someone who admittedly has skipped much of the discussion. No matter, yes, while it is true that this thread has seen its share of nonsense (see above), if you do read through the wealth of the material that has been posted, including more advanced matter that has been referenced and linked to, you may find that there is indeed some material of higher-than-average quality in this thread. I encourage you to read it, if you are interested.


Of course it isn't a characterization of the thread as a whole. At various points there has been good discussion. But then the some of the counterpoints from both sides have been absolutely content-free, and I think I saw the word 'idiot' get thrown around here and there, and people quoting qualifications and similar (which was when I started scanning).


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## Typetwelve (Jul 1, 2012)

I'm no expert...and far from a pro rider...all i can say is what I've found.

I spent a season on a SL2 gen Specialized Roubaix, and it wasn't the S-Works. The frame had give, I could even watch the forks move on really rough tarmac (I weigh in the 170's, BTW). It was a comfortable ride and I was plenty fast on it (for me...fast as in what I can do).

In 2012 I picked up a SL2 Tarmac...again, not even a S-Works model. The thing can be freaking punishing at times. In the current setup, I've had more "holy crap, this thing is harsh" comment given to me by various people. I took my bike to a local Trek store (good service) to have a 5800 group put on. When I got it back, their mechanic (a fellow, very experienced roadie) told me my bike was extremely responsive but "One of the most punishing bikes I've been on in some time". It is...it will perform father than I can currently push it, but that performance comes at a price.

In the end, the only reason I'm any faster on this Tarmac than on the Roubaix is that it is 2015 and I rode the Roubaix in 2012. I've just has 3 more years to improve as a rider is all.

My friend bought a new E5 Smartweld Allez...that thing is down right brutal. It is stiff as a board and puts every bit of road chatter right into every contact point of your body...but boy, is it stiff! I despised riding the thing...it is just brutal in stock form.

This is all my personal experience...and I fully understand that I am flawed and "mortal"...but I can say this, I had more fun on that Roubaix than I did any other...and it was "flexy".


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## Pirx (Aug 9, 2009)

Nereth said:


> Keep in mind we are in an industry where 0.5% change in efficiency would be huge. That's saving a few watts. Saving a single watt is not insignificant when you are pushing the limit. Writing things off as 'small enough to be negligible' should be done with great care. Without characterizing how large chainline losses are, I'm not sure I would agree with you that they don't matter. There is a paper that addresses it but I didn't feel like spending money, so personally I'm not sure, but it did say it was measurable (but yes, extremely small)


You mean this paper?

Here's the quote from the conclusions:


> It was found that chain line offset and chain lubrication have a
> negligible effect on efficiency under laboratory conditions.





Nereth said:


> Unclear, I would agree. But that leaves the door open for it to be, again, non-zero. Which again leaves the door open for people saying "My stiff frame feels faster" to not be guaranteed to be wrong.


Which is not disputed anywhere in this thread.



Nereth said:


> "Physics says it's not there so it's not"


Certainly my argument was a lot more differentiated than that.


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## Pirx (Aug 9, 2009)

HFroller said:


> BTW: I really don't understand why you insist on general conservation of energy arguments. One cannot apply them to the frame (or the bike) alone, because the frame is not a closed system when there's a rider sitting on it an riding it. Not even approximately.


Initially I thought I would reply with some more details regarding why I think your model is not a good one (talking about the fact that the sideways motion you are talking about is really a secondary effect, which is caused by introduction of a moment at the BB, which leads to torsion of same, and bending of the frame; and that such details are important, since they can provide the coupling between frame oscillation and propulsion that is missing in your model), but then I decided that this is really a direction that I do not want, and do not have to go to.

Like I said, and as you criticize above, I continue to believe that energy conservation arguments are the most helpful. So, what I will do now is fall back to my "mechanical rider" argument in this post. The system proposed in this example does include a "rider" as you rightly demand, but it shows that for the case of an "ideal rider" frame stiffness _cannot_ have any effect. As a consequence, _if_ there is any effect of frame stiffness on the bio-mechanical efficiency of the rider-bicycle system, it must be sought in imperfections of the bio-mechanics of the rider, and how those are affected, one way or another (that's an entirely different question, of course), by different degrees of frame deformation.

Let me know what you think about the argument put forward in that example. It's not impossible that I am overlooking something, but if so I can't see what it might be.


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## tvad (Aug 31, 2003)

Prix, when are you going to tie this thread in a bow and send the link to all the carbon bike manufacturers? This is scholarly information they need to have, don't you agree?


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## Pirx (Aug 9, 2009)

Nereth said:


> Keep in mind we are in an industry where 0.5% change in efficiency would be huge. That's saving a few watts.


By the way, I do not agree with this characterization of the industry, for a number of reasons, but that's a different story entirely. Now we're talking about economics and marketing... Oh, and at 300W, 0.5% is 1.5W, and 1.5W is really little. But again, that's a different story, too.



tvad said:


> Prix, when are you going to tie this thread in a bow and send the link to all the carbon bike manufacturers? This is scholarly information they need to have, don't you agree?


So you really think they are not aware of, and/or they would care one way or another about the facts I have been trying to drive home here?


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## tvad (Aug 31, 2003)

Pirx said:


> So you really think they are not aware of, and/or they would care one way or another about the facts I have been trying to drive home here?


Absolutely!...but why should you care what _they_ care about? They need this info, and you're the man for the job! Tally ho!


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## Pirx (Aug 9, 2009)

tvad said:


> Abslolutely...but why should you care what _they_ care about? They need this info, and you're the man for the job!


There's no job, since they have this "info".


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## tvad (Aug 31, 2003)

Pirx said:


> There's no job, since they have this "info".


Your elucidation needs to go beyond the 20 people who have read this thread. Spread the word. The wider community needs to know. Write an article for Bicycling, Cyclingtips, Peloton Magazine, Velo News, etc.

Don't allow your tree to fall in the woods unheard. 

Let your treatise be read!


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## HFroller (Aug 10, 2014)

Pirx said:


> ... talking about the fact that the sideways motion you are talking about is really a secondary effect ...
> 
> (...)
> 
> So, what I will do now is fall back to my "mechanical rider" argument in this post. The system proposed in this example does include a "rider" as you rightly demand, but it shows that for the case of an "ideal rider" frame stiffness _cannot_ have any effect. As a consequence, _if_ there is any effect of frame stiffness on the bio-mechanical efficiency of the rider-bicycle system, it must be sought in imperfections of the bio-mechanics of the rider


I tend to agree that the motion I’m describing is a secondary effect. But my model suggests that the stiffness of the frame is a factor. Therefore I think it’s incorrect to neglect it a priori because of general conservation laws. Other arguments are needed. However, I believe it's correct to point out that damping by the frame can be neglected. 

I must confess I don’t know what to think about a system consisting of an ideal, elastically deforming frame powered by a perfect motor. But I do think this Gedankenexperiment isn’t very enlightening. The biomechanical and biophysical properties of real riders play an essential role in the evaluation of frame flex, and real riders are not perfect motors.


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## Pirx (Aug 9, 2009)

HFroller said:


> The biomechanical and biophysical properties of real riders play an essential role in the evaluation of frame flex, and real riders are not perfect motors.


We agree completely on that part. 

Whether or not, and why or why not, you do find that Gedankenexperiment enlightening is a separate but interesting (to me) question also. I think I understand why you feel the experiment is not very enlightening, in that its outcome is certainly trivial from the point of view of mechanical science. Nevertheless, I still feel it is saying something of interest, in the sense that this message is not generally understood, to state that _if there are any advantages of a stiffer frame, then it would have to be not because a flexible frame "soaks up power", but because the motion of the rider on the flexible frame is less efficient_. 

The reason why it is useful to have this statement in mind is because it makes it clear that if somebody wants to claim an advantage in power efficiency of the stiffer frame, that person would have to demonstrate that indeed the motion of the rider on such a bike becomes more efficient. While this may indeed be possible (in certain cases only, perhaps?), it would require an appropriate rigorous investigation. No such study has ever been done, to my knowledge anyway, which means that the status of any statement regarding a relationship between power efficiency and frame stiffness remains uncertain. In simple words, nobody knows if a stiffer frame is better (for power efficiency).

Now, I would lean out the window and even go a bit farther, by saying the following: Given the very, very small changes in frame geometry involved (less than an inch deformation at the interface between the rider and bike, the pedal, at the very most; note this means that the _difference_ between deformation of existing road bike frames is probably less than half of that), it is clear that any changes in the kinematics and dynamics of the rider motion, and corresponding changes in the exact way the rider uses his/her muscles will be very, very small also. Finally, take into account results like the one discussed above, were no significant differences in pedaling efficiency were found for riders using cranks with lengths varying between 145mm and 195mm, which constitutes a much larger change in rider kinematics compared to what we are talking about here, then it becomes extremely implausible that frame flex or lack thereof would have any significant effect at all on power efficiency.

So, at this point my statement would be two-fold:

There is currently _no evidence_, neither theoretical nor experimental, for or against the thesis that stiffer frames provide better power efficiency in the rider-bicycle system.
It appears unlikely that, within the range of maximum frame deformations that are realistic for existing road bikes, variations of frame stiffness would have a noticeable effect on power efficiency.


Feel free to let me know what you think


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## Pirx (Aug 9, 2009)

tvad said:


> Your elucidation needs to go beyond the 20 people who have read this thread.


Well, I don't know, this thread now has more than 10,000 reads, and I doubt that's because 20 people read through it 500 times each, although I can't be sure, of course


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## tvad (Aug 31, 2003)

Pirx said:


> Well, I don't know, this thread now has more than 10,000 reads, and I doubt that's because 20 people read through it 500 times each, although I can't be sure, of course


Let's say 10,000 people each read it once, the need to submit an article to a wider audience is paramount. Get the word out. Don't delay!


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## myhui (Aug 11, 2012)

Is a bicycle frame blessed by a priest always stiffer than one not so blessed?


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## stevesbike (Jun 3, 2002)

Pirx said:


> Gee, what do you think? Perhaps, it might just be that I have no interest whatsoever in this guy's claims; as you might have been able to figure out by now, if _you_ had any interest in an honest debate. I think I have stated what my assertion is very clearly, and I have done so repeatedly. I have also explained the status of that quote you love to drag out, in the context of my argument. So, if you want to address the claim _I_ am making, then I might be interested. Otherwise, you are of course free to keep bashing any silly straw you like, but you'll have to excuse me for not participating in that game.


and you're still rattling on about nonsense. The "guy" in question is the person you quote in the first post. He is the author of the most dubious claim in cycling "science." The theory of "planing." 

More generally, you seem unaware of arguments from first principles. Let me help you out. According to the received view, in the limiting case, the work done in deforming the frame (strain energy) is completely returned as forward propulsion. This is questionable - for one, it results in measurably decreased drivetrain efficiency due to friction. Second, the ONLY empirical study of this (Damon Rinard's at Cervelo) found that it is returned out of phase and so not translated into forward propulsion. 

But that notwithstanding, the result on the received view is that a flexible frame is as efficient in the limiting case as a frame that does not flex. 

The only other interesting case is one in which a flexible frame increases what we can call effective input energy (over time, integrated as input power). This is Heine's 'planing" theory. Since the best power meter is accurate to ~1.5%, this should be easily observable if it were a significant factor. No one has detected it. Certainly, Heine's claim is patently false. You continue to claim that the phenomena in question is so complex that it cannot be adequately modeled. Again, that's dubious - you are engaging in obscurantism throughout this thread. However, we don't actually need to model the phenomena in question since it makes a prediction as per the above re effective input power. This prediction is disconfirmed daily. As I mentioned before, if a flexible frame increased effective input power, we would see it in our power data, in average speeds across generations in racing, and elsewhere.

You have a lot of bluster, lots of smoke, but very little light.


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## Z'mer (Oct 28, 2013)

Pirx said:


> ...which is caused by introduction of a moment at the BB, which leads to torsion of same, and bending of the frame;
> 
> Like I said, and as you criticize above, I continue to believe that energy conservation arguments are the most helpful. So, what I will do now is fall back to my "mechanical rider" argument in this post. The system proposed in this example does include a "rider" as you rightly demand, but it shows that for the case of an "ideal rider" frame stiffness _cannot_ have any effect. As a consequence, _if_ there is any effect of frame stiffness on the bio-mechanical efficiency of the rider-bicycle system, it must be sought in imperfections of the bio-mechanics of the rider, and how those are affected, one way or another (that's an entirely different question, of course), by different degrees of frame deformation.


Agree with your analysis of the forces in the first sentence above, I think this may have been the first time you posted a concise statement of the problem like this. 

Also think your mechanical rider for me is somewhat OK, but not illuminating as it does not really add anything, or make the result intuitively obvious to anyone. 

Why? If you understand the model, assumptions, and analysis in the 1974 Calspan paper, they derive the same results using math, but more importantly, in so doing, also show the limitations of the assumptions made. Those same assumptions apply to your mechanical rider, and if "real" riders are outside the box of the most important assumptions, everything in the "results" - i.e. energy is conserved, blows up. 

So what are the most important assumptions?

I think the MOST important assumption to the perfect rider model, is that the torque versus crank angle plot is a perfect sinewave type curve, with maximum torque at 90 degrees from 0 (TDC), and zero torque at 0 and 180 degrees. This, by far, is the least talked about, but most important variable in this whole thread. Which is now 16 pages deep, and has never really been discussed. 
If this assumption is not met, the perfect rider becomes a ghost, and all models assuming the perfect rider become invalid as well. 

Suggest people spend a few minutes looking at past research targeted at this specific topic. It is varied, but not in agreement. The newest research based on modern data acquisition techniques using pro riders appears to be most accurate. 
Looks like the more power riders put out, the more the curve deviates from the perfect model. At least this is my takeaway.


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## Jwiffle (Mar 18, 2005)

stevesbike said:


> and you're still rattling on about nonsense. The "guy" in question is the person you quote in the first post. He is the author of the most dubious claim in cycling "science." The theory of "planing."
> 
> More generally, you seem unaware of arguments from first principles. Let me help you out. According to the received view, in the limiting case, the work done in deforming the frame (strain energy) is completely returned as forward propulsion. This is questionable - for one, it results in measurably decreased drivetrain efficiency due to friction. Second, the ONLY empirical study of this (Damon Rinard's at Cervelo) found that it is returned out of phase and so not translated into forward propulsion.
> 
> ...


I missed where Pirx stated a flexy frame increases power transfer. Has seemed to me he has only argued that it has not been proven, and is unlikely to be the case, that a stiff frame increases power transfer.


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## Pirx (Aug 9, 2009)

stevesbike said:


> You have a lot of bluster, lots of smoke, but very little light.


Who knows, maybe you're right; I'm certainly in the dark as to what you're going on about. Certainly I have never claimed anything as silly as "the phenomena in question [are] so complex that [they] cannot be adequately modeled". Otherwise, no further comment. Now go ahead and do another one of your little victory jigs, why don't you. It's been fun the last time.



Z'mer said:


> I think the MOST important assumption to the perfect rider model, is that the torque versus crank angle plot is a perfect sinewave type curve, with maximum torque at 90 degrees from 0 (TDC), and zero torque at 0 and 180 degrees.


No such assumption is required in my "perfect rider" model; as a matter of fact, you can introduce arbitrary torque-versus-angle variation without affecting the fundamental outcome: The required input power cannot depend on frame stiffness and is always exactly the same as the output power.



Jwiffle said:


> I missed where Pirx stated a flexy frame increases power transfer.


Yep, so do I. Pirx has never said anything of that sort. But who cares, beating up straw men is so much fun, innit?


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## Z'mer (Oct 28, 2013)

Pirx said:


> No such assumption is required in my "perfect rider" model.


What are the assumptions then? What is the assumed torque versus crank angle plot? Or, are you saying it is unimportant, and does not matter? 
And, please explain briefly how this model closely simulates a typical experienced rider? If not, why even propose it? 

I can also easily show how a battery powered bike with a 100% efficient regenerative electric motor "conserves energy". But is that in any way representative of a human powered bike? 
Does a guy who rides a fixed gear track bike up a steep hill get anything back when he coasts down the other side? Does he "conserve energy"?

The model for the electric motor bike above would. So what. Why mix up 2 different and completely situations. From a thermo view, isentropic and non-isentropic processes.


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## myhui (Aug 11, 2012)

Z'mer said:


> What is the assumed torque versus crank angle plot?


This one I do care about. When I step on it for just those 90 degrees of chainring rotation, a good bike will go farther than a lesser bike at the end of those 90 degrees of chainring rotation, and that's important for me.


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## Pirx (Aug 9, 2009)

Z'mer said:


> Or, are you saying it is unimportant, and does not matter?


That's what I said: It doesn't matter, and never even enters into consideration.



Z'mer said:


> And, please explain briefly how this model closely simulates a typical experienced rider?


As briefly alluded to in my original post, you can make this model as similar as you like to a real rider, in that you are free to model sizes and mass distributions of limbs and torso of a real rider as closely as you wish. The only condition is that you need to replace the rider's muscles with perfectly efficient actuators (and the joints need to be friction-free, etc.). Note that, once you have those actuators, you can also have them move in the exact same way as the muscles of a real rider. The only difference will be that if those "artificial muscles" extend under a force (eccentric contraction), they will indeed recover energy, which human muscles do not. Is that good enough for you?

I will add that, yes, you do have a point hidden in your post, but it is one I have never disagreed with, and that has in fact always been a part of my position: Yes, absolutely, the question of whether or not a stiffer frame is more power efficient than a more flexible one is indeed inextricably linked to the peculiarities of how the human body propels a bicycle. Our current knowledge of the rider-bicycle system is insufficient to determine the relationship between frame stiffness and power efficiency, for a given rider. Even if there is an effect that is significant enough to be worthy of consideration, it may be that it depends on the individual rider and the specific geometry of the bike s/he has chosen, and could thus be considered an aspect of fit. There could be a point of optimal stiffness, so that both lower and higher stiffness would be suboptimal, etc.

Like I said, my guess is that any effect, if it exists, will in fact be too small to be of interest, but I will admit that this is an educated guess, and nothing more.


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## Jwiffle (Mar 18, 2005)

myhui said:


> This one I do care about. When I step on it for just those 90 degrees of chainring rotation, a good bike will go farther than a lesser bike at the end of those 90 degrees of chainring rotation, and that's important for me.


Huh? Talk about a lack of understanding of physics. If your cranks go around 90 degrees, the bike is going to go same distance whether you exert 1 watt or 1000 watts. That's just simple gear ratio.

If a flex frame did hinder power transfer, it would hinder how quickly you could actually turn the crank. So it wouldn't go any further, just faster.


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## myhui (Aug 11, 2012)

Jwiffle said:


> If a flex frame did hinder power transfer, it would hinder how quickly you could actually turn the crank. So it wouldn't go any further, just faster.


I talk like a LBS salesman at times. You caught me there!


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## HFroller (Aug 10, 2014)

Pirx said:


> As briefly alluded to in my original post, you can make this model as similar as you like to a real rider (...)


I don’t know about perfect models that are similar to realistic riders, but I think that *in general* your argument of perfect energy conservation in a system doesn’t work. And because it’s a very general argument, this means the argument doesn’t work.

Assume you have a perfect, non-flexible bike, one that stays magically upright without rider. It is rolling. 

On the bike are two identical springs that make two identical masses M oscillate. Perfect, weightless springs, masses gliding on the top tube (without friction!) in an horizontal plane (so no influence of gravity), in the plane of the frame etc. etc. As perfect and energy conserving as one can imagine. These springs simulate the effect of elasticity. To keep things simple, I postulate that the masses are oscillating in opposite directions. The “center of mass” of the two oscillating masses doesn’t move relative to the bike. Because of this, the bike rolls with a constant velocity. It doesn’t feel the masses are oscillating. 

To simulate the influence of the rider, I postulate that the springs were loaded with a force F. 
A cyclist pushed on the spring with F, suddenly removed his foot and the spring started to oscillate. 

Now take two of these bikes with exactly the same total energy. The sum of (potential energy of the oscillating masses) + (kinetic energy of the masses) + (kinetic energy of the bike) is the same. 

Assume that the springs were loaded with exactly the same force. 
But also assume that the modulus k of the springs on bike A is higher than the modulus k’ on bike B. Bike A is “stiffer”. 

Then bike A has a higher velocity – even if its total energy is the same. Strange, but true. Unrealistic example, but one has to admit that basic mechanics is fun. 

Important remark: A is not faster because B looses energy. The bikes have the same total energy and everywhere perfect energy conservation is assumed. Then why A is faster? Physically, the reason is simple: the total energy of the masses attached to the springs is lower when the modulus is higher (when the bike is stiffer). There’s more energy left over for the forward movement of the system bike + oscillating masses.

EDIT.
I'm not claiming that the difference in the stiffness of the springs makes bike A much faster than B. The effect may be small. But I'm more and more convinced that one cannot write off the importance of stiffness with a general argument based on energy conservation.


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## Pirx (Aug 9, 2009)

HFroller said:


> Then bike A has a higher velocity – even if its total energy is the same. Strange, but true.


I'm not sure what you feel is strange about that: You converted a fixed amount of input energy from the rider into both internal energy (of the frame oscillation) and external, kinetic energy. For the more flexible frame, more energy goes into the frame oscillation, so less is available for kinetic energy. Duh.



HFroller said:


> I'm not claiming that the difference in the stiffness of the springs makes bike A much faster than B. The effect may be small. But I'm more and more convinced that one cannot write off the importance of stiffness with a general argument based on energy conservation.


Good, so let's look at the numbers. Before going there let me say that this is a nice little model that's certainly worth considering. Essentially what you are saying, correctly, is that the more flexible frame will store more energy in its oscillation, which is trivially true (you have already mentioned the F^2/k proportionality of the stored energy earlier).

However, notice that this difference, for steady-state riding, will only exist in the transient phase between the state of complete rest (no bicycle motion and no frame oscillation) and the statistically stationary state (we don't need periodicity, of course, statistical stationarity is sufficient). 

Now, back to the numbers: Earlier in the thread we had various estimates for the energy deposited in the frame oscillation. The highest one of these gives us 4% of the energy of the first pedal stroke (one side) to be deposited in the frame oscillation. After that, no more energy is deposited, so no further difference between the two frames exists.

Thus, sure, you will lose a tiny bit of energy during the first pedal stroke, but, duh, that was obvious (is it my turn now to tell you that I do not find this result particularly interesting? ) from the get-go (pun intended). So, you'll see a tiny effect during the first pedal stroke, and no effect after that. I don't think that this is of much consequence for the conclusion I have presented, and I don't see how this would affect my general energy conservation argument in the least. Well, except for adding an inconsequential caveat for the transient startup-phase. I don't think anybody (other than myhui) will care much...

P.S.: I forgot to say, and just in case this is not/was not clear, in my model I had of course assumed the statistically stationary case, so I was explicitly (well, I guess not that explicitly; yeah, yeah, I didn't say that) _not_ interested in any transients. I imagine tons of people now jumping on that, saying that they always knew that the stiffer frame _accelerated_ faster, and on and on... [Sigh...]

In any case, those energy conservation arguments work perfectly fine for the case I was interested in and, correctly understood, they also work, _mutatis mutandis_, for the transients, see above.


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## HFroller (Aug 10, 2014)

Pirx said:


> I'm not sure what you feel is strange about that: You converted a fixed amount of input energy from the rider into both internal energy (of the frame oscillation) and external, kinetic energy. For the more flexible frame, more energy goes into the frame oscillation, so less is available for kinetic energy. Duh.
> 
> (...)
> 
> So, you'll see a tiny effect during the first pedal stroke, and no effect after that. I don't think that this is of much consequence for the conclusion I have presented, and I don't see how this would affect my general energy conservation argument in the least.


In my perfectly energy-conserving bike with springs contraption, the bike with the stiffer springs moves faster _all the time_. 
There's nothing "transient" about the effect.
And what's more: the fact that the velocity is _permanently _higher is _a direct consequence of the assumed perfect energy conservation_. 

It's more than possible you'll have to let go energy conservation if you want so see transient effects. 

One can question the assumptions in my model, but its only aim is to show that "general energy conservation arguments" don't get you anywhere in this discussion. It doesn't have to be realistic to show that.


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## myhui (Aug 11, 2012)

HFroller said:


> And what's more: the fact that the velocity is _permanently _higher is _a direct consequence of the assumed perfect energy conservation_.


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## stevesbike (Jun 3, 2002)

Pirx said:


> Now, back to the numbers: Earlier in the thread we had various estimates for the energy deposited in the frame oscillation. The highest one of these gives us 4% of the energy of the first pedal stroke (one side) to be deposited in the frame oscillation. After that, no more energy is deposited, so no further difference between the two frames exists.


spherical cows much? This is empirically false. Conservation of energy is also a red herring. You have yet to provide any evidence that strain energy is returned in a form that results in forward propulsion. It could be lost in friction, simply returned in the form of raising the rider since the seattube deformation could result in slightly lowering the rider, be out of phase etc. You also haven't consider the case of carbon bikes and damping/energy dissipation, which would depend on the specifics of the laminate structure. There's conservation of energy in the foot/shoe interaction - but the energy that is used to compress the sole isn't returned as forward propulsion. It just raises the foot out of phase. There's no a priori reason (and in fact some empirical evidence) that this is the case for frame deformation. Again, now 17 pages and nothing more than idle musings on your part.


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## Pirx (Aug 9, 2009)

HFroller said:


> In my perfectly energy-conserving bike with springs contraption, the bike with the stiffer springs moves faster _all the time_. There's nothing "transient" about the effect.


Well, technically this _is_ a transient effect, but you are right that you, kind of, retain some speed advantage.

Also, what you're forgetting is the outside world, which is not energy conserving, since you're working against aerodynamic drag and rolling friction. Without that, sure, your stiffer bike will always be a tiny little bit faster, but the speed of both bikes would increase indefinitely, to infinity and beyond.  



HFroller said:


> One can question the assumptions in my model, but its only aim is to show that "general energy conservation arguments" don't get you anywhere in this discussion. It doesn't have to be realistic to show that.


My energy conservation arguments are just fine for the statistically stationary case, but you have a point, in principle, that the transient you are talking about may be of interest. I have argued that this effect is negligible, but you may or may not believe that. So, rather than having this discussion in a vacuum, let's put some meat on those basics, and see where that takes us.

So, let's just do some calculations. Hang on guys, I know this is long, but I promise you'll find this interesting, on both sides of the argument.

Let's assume we're pedaling at just 90rpm, so the pedal stroke lasts a third of a second (roughly, I'm just assuming a half revolution of the crank). Let's also give you someone sprinting at a respectable 900W, and use the (very high, IMO) estimate of 4% of energy deposited in the frame oscillation. That makes 900*0.3*0.04=0.4J that's lost to propulsion. Let our rider plus bike weigh just 160lbs, so that's roughly 72kg give or take. Then, assuming all of that energy is converted into kinetic energy rather than frame flex (infinitely stiff frame), then we get v=sqrt[2E/m]=2.74m/s=6.15mph if the full power is available, and 2.68m/s=6.03mph if we subtract the 0.4J that goes into the frame flex. so there's an advantage of an infinitely stiff frame of 0.12mph, in a sprint from a standing start.

How much is that? Well, I will say that that may be enough to be of interest to a sprinter. So let's see what the advantage is if we integrate the equation of motion to get a better idea.

Here's what I assume: 

I take a rolling resistance of Crr=0.0048 from here, and let's have a rider in the drops, which gives a drag coefficient of CD=0.88 and a frontal area of A=0.32 m^2 from this site. You can check that those numbers give you a reasonable dependence of power on speed. 

As above, my beast of a rider is assumed to be able to put out 900 Watts for as long as it takes, and he weighs 145lbs and uses a bike weighing 15lbs.

We'll assume an otherwise perfect drivetrain, so there's no other losses anywhere. I use standard air density of rho=1.225 kg/m^3 (sea level standard atmosphere) and a gravitational constant of g=9.81 m/s^2.

I'm looking at two different frames, one perfectly stiff (zero flex), the other soaking up 4% of the input power during the first pedal stroke (half crank revolution). I'm going to assume that the rider is going at a constant 90rpm. Yes, that means he needs a perfect continuously variable transmission, but that assumption will do for us. The rpm assumption only comes in to calculate the time during which reduced power is available.

With these assumptions, I am going to integrate the equation of motion in the form derived from the equation for kinetic energy, taking the first derivative w.r.t. time, so we have

m v(t) d v(t)/dt=P(t)-m g Crr v(t) - 1/2 rho A CD v(t)^3

P(t) is 0.96*900W for the first pedal stroke, and 900W after, for the flexible frame; it's just a constant 900W for the perfect frame. We note in passing that the assumption of finite power at t=0 leads to a singularity in this equation if we assume a standing start since it would require infinite torque at t=0. We can deal with that however, simply by starting with a very small but nonzero velocity (make it 0.01mph if you wish).

So, I whipped up a bit of code to integrate the equation of motion, and here's what we find:

A) Sprint from a standing start
This is somewhat academic, but it will give you the maximum benefit of a stiff frame. Result: After integrating the velocity to find the distance the sprinter travels, we get:

For the flexible frame, 0.617m after a third of a second, 411.528m after 30 seconds, and 918.383m after a minute.
For the perfect frame, 0.630m after a third of a second, 411.727m after 30 seconds, and 918.586m after a minute.
So, the perfect frame is ahead of the flexible one by 13mm after a third of a second, by 199mm after 30 seconds, and by 203mm after 60 seconds. In other words, after a minute we have an advantage of the perfect frame of roughly 8 inches.

B) Sprint from 20mph
A much more realistic scenario, needless to say. Here's the numbers:

For the flexible frame, 3.009m after a third of a second, 448.701m after 30 seconds, and 956.316m after a minute.
For the perfect frame, 3.012m after a third of a second, 448.826m after 30 seconds, and 956.443 after a minute.
So, the perfect frame is ahead of the flexible one by 3mm after a third of a second, by 125mm after 30 seconds, and by 127mm after 60 seconds. In other words, after a minute we have an advantage of the perfect frame of roughly 5 inches.

So, where does this leave us? First of all, keep in mind that the above calculations use the most favorable scenarios for proponents of the benefits of the stiffer frame. In particular, we are comparing a very flexible frame with a perfect one. If we did a more realistic comparison of, say, the stiffest currently available carbon frame with the same model 10 years ago, the differences would be much, much smaller.

Second, however, I will say that for a sprinter, even an advantage of an inch or two in a world championship may not be negligible, and my calculations show that a difference of an inch or so may be in the realm of what's possible to gain with a stiffer frame.

So, at the end of the day I think you do have a point that I will concede: In very hard sprint scenarios, there may indeed be a tiny benefit of frame stiffness. We need to keep in mind that in such a sprint scenario, many other variables come into effect as well. For example, the exact line that the rider chooses (or is forced to choose) will, over a distance of several hundred yards, typically lead to much larger differences in distance that the rider needs to travel than just an inch or two. 

I'm truly looking forward to the responses to this post


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## Pirx (Aug 9, 2009)

stevesbike said:


> spherical cows much?


Blah blah blah. You know, Steve, I highly recommend you just stay out of this. By now it is clear to everyone, but absolutely every single person having followed this thread, that you have exactly zero to contribute. But, by all means, if you enjoy making a fool of yourself, carry on.


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## robt57 (Jul 23, 2011)

Pirx said:


> Blah blah blah. You know, Steve, I highly recommend you just stay out of this. By now it is clear to everyone, but absolutely every single person having followed this thread, that you have exactly zero to contribute. But, by all means, if you enjoy making a fool of yourself, carry on.


Did you not get the relevant conundrum, or just deem yet another participant to open public forum yet another muggle? Try not to be such an intellectual snob. 

Have you digitally pissed thought the internet onto this thread ??

I just have to put you on my ignore list, your ability outside of being obviously smart to be a dick is disgusting.


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## Pirx (Aug 9, 2009)

robt57 said:


> Did you not get the relevant conundrum, or just deem yet another participant to open public forum yet another muggle?


I would consider my response appropriate for the post I responded to. You are free to disagree, of course.


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## HFroller (Aug 10, 2014)

Pirx said:


> I'm looking at two different frames, one perfectly stiff (zero flex), the other soaking up 4% of the input power during the first pedal stroke (half crank revolution).
> 
> (...)
> 
> P(t) is 0.96*900W for the first pedal stroke, and 900W after, for the flexible frame; it's just a constant 900W for the perfect frame.


Thanks for the calculation and the work that went into it.

If I understand you correctly, you assume that there's only energy loss during the first pedal stroke. 
But if you read the article that cites that famous 4 %, the authors also say this:



> The true intent of a stiff frame is to transfer energy efficiently from the cyclist to the rear wheel. This implies that the designer should minimize the amount of energy that goes into flexing (straining) the frame. Some of this strain energy might be recoverable (i.e., released in such a way as to add power to the rear wheel). But we know of no measurements that show how much is recovered.


I a realistic situation it is possible (and plausible) that the strain energy is not completely recoverable because of the biomechanics and the biophysics of the rider.

Now look at your formula but take a steady state with dv/dt = 0. Say a time trial with constant speed. Take P = 450 with gives about 48 km/h or 30 mph - a good order of magnitude for a TT of an hour. 

A non-recoverable loss of 1 % will make a rider with the same output lose 13.5 s over that TT.
2 % makes him lose 24.4 s.


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## Pirx (Aug 9, 2009)

HFroller said:


> If I understand you correctly, you assume that there's only energy loss during the first pedal stroke.


Correct. Note that for these calculations my intent was only to illustrate the consequences of your model (which assumed no further losses after the frame oscillation has been excited), which in turn was meant to look at an aspect of the behavior of my "perfect rider"-bicycle system, I think.



HFroller said:


> I a realistic situation it is possible (and plausible) that the strain energy is not completely recoverable because of the biomechanics and the biophysics of the rider.


Yes, I do not disagree that this may be possible. Whether that's _plausible_ is another matter. My point has been all along that we are not in a position to decide the question. As a matter of fact, as far as we know it might just as well be that the different bio-mechanics of the flexible frame leads to improved metabolic and/or bio-mechanical efficiency of the rider. And, no, this statement of mine really has nothing to do with the unfortunate quote of Heine I had included in my OP, or any of his work.

Also see here for a look at the complexities of this question from a slightly different perspective. You will notice that their "compliant model" could be viewed as another way to model the effect of a flexible frame (as the authors briefly mention in passing in their discussion on page 6).



HFroller said:


> A non-recoverable loss of 1% will make a rider with the same output lose 13.5 s over that TT.


Yes, but we don't know anything about whether or not such a loss exists. As an aside, in a time-trial situation at 450W, I would expect the _total_ energy to go into flexing the frame to be less than 1% (based on the maximum torque being at most half of what it was in my 900-W scenario) of the input energy. So a 1% loss would mean a total loss of all of the energy used to flex the frame. That would seem to be an extremely unlikely case, IMO.

So, once again, I do allow that frame flex may lead to losses; or it may lead to improved efficiency. My claim is simply that nobody knows.


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## ibericb (Oct 28, 2014)

HFroller said:


> ...
> 
> But if you read the article that cites that famous 4 %, the authors also say this:
> ...
> ...


I don't want to disrupt this intriguing discussion between you and Pirx, but I want to highlight a couple of points that have been brought out in this thread previously, pertinent to the numbers about how much might be lost to frame distortions.

First, the 4% number is a maximum that has been estimated for any reasonable frame. That came from a very early use of finite element analysis. Much more recently, that number was also cited by the famed Damon Rinard from his work at Cervelo. Contrary to what stevesbike has repeatedly asserted, Rinard's number came from a combination of static measurements (deflection of the BB under a fixed load), and finite element simulations. Further from Rinard, he determined that by far most of the energy stored in the frame from BB flex in pedaling is actually returned, and is not lost from propulsion (there is no out-of-phase issue). This was also determined via finite element simulations using a typical pedal force vs rotation profile in the calculations (not instrumented frames with riders as has been suggested by others). As Rinard finalized it, he would look to spend money elsewhere for speed because difference arising from frame stiffness are negligible.

So, if the energy were in fact lost, absorbed somewhere or used to do other work, then yes, the differences you cite would be a real and serious concern. But by all credible attempts to quantify any losses from propulsive power due to frame flexibility that we have seen to date, that just does not happen to any degree of concern or certainty. 

We now return you to the discussion in progress.


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## Pirx (Aug 9, 2009)

ibericb said:


> I don't want to disrupt this intriguing discussion between you and Pirx, but I want to highlight a couple of points that have been brought out in this thread previously, pertinent to the numbers about how much might be lost to frame distortions.
> 
> [...]
> 
> We now return you to the discussion in progress.


Oh no, thanks very much for this very appropriate reminder... 

P.S.: I have lost track of what was where by now, can you remind me where the results by Rinard you refer to below were reported? Thanks!



> Further from Rinard, he determined that by far most of the energy stored in the frame from BB flex in pedaling is actually returned, and is not lost from propulsion (there is no out-of-phase issue). This was also determined via finite element simulations using a typical pedal force vs rotation profile in the calculations (not instrumented frames with riders as has been suggested by others).


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## Z'mer (Oct 28, 2013)

Pirx said:


> Correct. Note that for these calculations my intent was only to illustrate the consequences of your model (which assumed no further losses after the frame oscillation has been excited), which in turn was meant to look at an aspect of the behavior of my "perfect rider"-bicycle system, I think.
> 
> ...So, once again, I do allow that frame flex may lead to losses; or it may lead to improved efficiency. My claim is simply that nobody knows.


As discussed earlier, the assumption is the frame movement under pedaling force occurs at a frequency well below natural resonance. 
The loss, if any, is felt on every pedal stroke. 

On the second point - there is a continued theme here on your part, that "nobody knows". Why don't you say instead, "I don't know". 

How do you assume to know what everyone else who has studied the subject knows? Do you really think there is no way to measure this? And no one has? You continue to make this into a big unknown unsolved mystery. 
It's not, except in your way of thinking, which is likely because you are stuck in your thinking using the tools you know best.


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## ibericb (Oct 28, 2014)

Pirx said:


> P.S.: I have lost track of what was where by now, can you remind me where the results by Rinard you refer to below were reported? Thanks!


See this stem, links to reference pointed to were included.


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## Pirx (Aug 9, 2009)

Z'mer said:


> As discussed earlier, the assumption is the frame movement under pedaling force occurs at a frequency well below natural resonance.
> The loss, if any, is felt on every pedal stroke.


NO. Not for the model in question.

As for the relationship of pedaling frequency to eigenfrequency of the frame oscillation, I'm not sure where you would like to go with this. It is exactly _because_ we are well away from the eigenfrequency that we can claim there's no energy transfer to the frame in the case with no material damping. Let me repeat this for you: _There is no transfer of energy into the frame, on average_.



Z'mer said:


> On the second point - there is a continued theme here on your part, that "nobody knows". Why don't you say instead, "I don't know".


That would be because _nobody_ knows. There are no published results, anywhere at all, that would demonstrate the claimed effect, or its opposite.



Z'mer said:


> How do you assume to know what everyone else who has studied the subject knows?


Well, sure, technically it is possible that someone has done the appropriate experiment, and has not told anyone about it. I would submit that that's quite an unlikely scenario.



Z'mer said:


> Do you really think there is no way to measure this?


No, of course not. I never said nor implied anything as silly as this. As a matter of fact, I have suggested, repeatedly, that somebody should do such an experiment.



Z'mer said:


> And no one has?


Not to my knowledge, and I know a thing or two about the general subject, plus I know quite a few people who know the specific area of bicycle mechanics a lot better than I do. 



Z'mer said:


> You continue to make this into a big unknown unsolved mystery.


Your interpretations of what I wrote are quite, shall we say, unusual. There is no big mystery at all, and it is easy to describe ways to perform an experiment that would test the claims in question rigorously. For example, plop someone on an appropriate test bike (note that the term "appropriate test bike, however, already hides quite a bit of complexity), and measure both power output at the wheel and metabolic cost (say, via O2 consumption), and do so accurately. Of course, all of this is a lot easier said than done. I think you underestimate the effort to actually do such an experiment with the kind of accuracy that is needed. Sure, it's certainly possible, but somebody would have to invest a significant amount of time and money to do this, but most everybody has a busy life...



ibericb said:


> See this stem, links to reference pointed to were included.


Thanks!


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## ibericb (Oct 28, 2014)

A fundamental issue questioned by several on the effect of frame stiffness or flexing on power development comes down to timing or "phase" of the return of any energy stored in the frame. That is, at what point in the pedal circle is the stored energy returned, and can that return be translated into propulsive power via interaction with the motion of the cyclist foot against the pedal? As best I can guess, this would be related to instantaneous power, as opposed to average power over the cycle. Previously I raised this question when an adverse effect was argued, but so far there has been no reply. So I continue to scratch my head over that - to what extent is instantaneous power vs. average power over a pedal cycle determinant of bicycle performance?

That question brings me to a fundamental consideration of the basics of power development. The argument that increased frame flexing, and energy storage, diminishes the efficiency of pedal applied force into propulsive power is predicated largely upon the consideration of pedal force alone. But power development has an additional variable over a pedal cycle, and that is angular velocity. In most equations that relate applied pedal force to power assume that angular velocity is a constant, and hence substitute cadence (along with the required constants) for angular velocity. However, as this work shows, the angular velocity around a pedal circle is in fact not constant. It varies considerably around the circle. Hence any determination of the true instantaneous power to be derived from a cyclists application of force to a pedal must consider also the variation in angular velocity that occurs around the circle. This further underscores the rather significant complexity in a dynamic consideration with a cyclist actually pedaling, power development, and the return of any energy stored in the frame from frame deflection. 

Not germane to the discussion in this thread, but worth noting, is the real variable nature of pedal angular velocity also draws into question the validity of power measurements from strain gauges when the power information derived assumes a constant angular velocity based on cadence.


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## Pirx (Aug 9, 2009)

Hmm, this is indeed very intriguing. Indeed, I had naively assumed that crank angular velocity should be directly tied to the translational velocity of the bike+rider system, and that this velocity should be fairly constant (based on an inertia argument). The paper you cite, in contrast, shows very significant oscillations of angular velocity, which will indeed need to be taken into account. I am fairly certain that part of the story will be relative motion of the bicycle underneath the rider which, now that I think about it, may well be substantial in a hard standing sprint. Thanks for bringing this aspect up!

P.S.: As an aside, those phase angle arguments that are brought up every now and then are largely misguided. Without going into the gory details, it is important to note that the phase angle of a parametrically excited second-order linear oscillator (which is what our bicycle frame is) follows from the excitation and its frequency, and is _not_ an independent variable. Attempting to prescribe both of these variables leads to an ill-posed problem. In short, the phase of the frame oscillations of a frame with no internal damping will adjust itself automatically such that the energy exchange becomes zero, on average. This does not directly address the question of conversion of frame internal energy into kinetic energy, but it is an important fact to keep in mind.


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## ibericb (Oct 28, 2014)

FWIW - Coach Alex Simons commented on variations in angular velocity, and the attendant impact on power meter data validity, via his blog earlier this year, here and a few days later here. Some interesting observations on crank angular velocity variations therein.

The angular velocity variation, along with any effect of frame movement on effective force, brings me back to the bio- mechanics/dynamics questions about how frame flex or movement might alter a cyclists application of force.


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## HFroller (Aug 10, 2014)

ibericb said:


> FWIW - Coach Alex Simons commented on variations in angular velocity, and the attendant impact on power meter data validity, via his blog earlier this year, here and a few days later here. Some interesting observations on crank angular velocity variations therein.
> 
> The angular velocity variation, along with any effect of frame movement on effective force, brings me back to the bio- mechanics/dynamics questions about how frame flex or movement might alter a cyclists application of force.


Purely theoretically, angular velocity variations are not necessarily a problem. One can describe these variations with a Fourier series and the resulting differential equation - if it is linear - can be solved if it can be solved for a simple driving force Fsin(wt). 



> But by all credible attempts to quantify any losses from propulsive power due to frame flexibility that we have seen to date, that just does not happen to any degree of concern or certainty.


I've said more than once that I don't know how large the influence of frame flex is. I'm only questioning some of the arguments offered here to claim that it's a myth. 

General energy conservation arguments don't work. I've constructed a counterexample based on nothing but general energy conservation arguments. 

Then there are more realistic arguments, for example the formula that Pirx calculated. The problem with such a formula is that the results depend on the input. Pirx concluded that the effect of frame flex is negligible, in my reaction I gave an example of an input with a result that might worry Tony Martin. 

So what is the input? I certainly don't claim to know. But one cannot conclude from such a formula that frame flex is unimportant - _it depends on the input_. The formula gives you the result you want, in a certain sense. 



> As for the relationship of pedaling frequency to eigenfrequency of the frame oscillation, I'm not sure where you would like to go with this. It is exactly _because_ we are well away from the eigenfrequency that we can claim there's no energy transfer to the frame in the case with no material damping.


That is a surprising statement. As I remarked earlier: assuming that the driving frequency is well under the eigenfrequency is physically equivalent to neglecting the kinetic energy of the oscillating movement of the frame. The only energy in the frame that counts is the potential energy - and if the frame makes an oscillating movement, that potential energy changes all the time. _There has to be an exchange of energy all the time between the frame and the other part of the system (i.e. the rider)_. This is true even if there's no damping.



> Without going into the gory details, it is important to note that the phase angle of a parametrically excited second-order linear oscillator (which is what our bicycle frame is) follows from the excitation and its frequency, and is _not_ an independent variable.


I agree.
However ... and I'm too lazy today to check it ... I thought the phase angle I'm agreeing with is different from zero only when there's damping. I also thought we were neglecting damping. 
Perhap it's another phase?


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## Pirx (Aug 9, 2009)

HFroller said:


> > It is exactly because we are well away from the eigenfrequency that we can claim there's no energy transfer to the frame in the case with no material damping.
> 
> 
> That is a surprising statement.


Oops, sorry, I forgot to add "no energy transfer to the frame _on average_" in the sentence of mine you quoted. You are of course correct that energy is constantly swapping back and forth between the rider and the frame.

I could quibble with the way you are talking about kinetic energy of the frame being neglected, but I trust you know this stuff well enough that a lecture on the mass-spring system is the last thing you need, so I won't. 

Oh, and for the forced, undamped oscillator you'll in general see both the forcing frequency and the eigenfrequency in the solution (so you get essentially a periodically modulated sine), so the solution is quasi-periodic, in general, unless the ratio of excitation and eigenfrequency is a rational number. At least that's what I remember, and I'm too lazy to look it up right now myself...


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## myhui (Aug 11, 2012)

On a trainer, you can compare power measured at the crank versus power measured at the wheel, and do this for frames with different stiffness.

You can also integrate that over a minute with maximum effort from the rider.


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## HFroller (Aug 10, 2014)

Pirx said:


> Oops, sorry, I forgot to add "no energy transfer to the frame _on average_" in the sentence of mine you quoted. You are of course correct that energy is constantly swapping back and forth between the rider and the frame.


Yes, but Z'mer wrote



> As discussed earlier, the assumption is the frame movement under pedaling force occurs at a frequency well below natural resonance.
> The loss, if any, *is felt on every pedal stroke*.


And he's right. 

I've said everything I had to say in this discussion. 
It was nice, but it's time for other things.


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## aclinjury (Sep 12, 2011)

suggestion:

build 2 similar carbon frames that have different stiffness level

then lock the frame into a trainer, with a rear wheel

now have a machine pedal the bike (as if it was a rider) mimicking a rider, with varying angular velocities

now measures the relevant data (speed, force) at both the crank and at the wheel.

compare the data gather at the crank and at the wheel, and we should see whether frame stiffness plays a significant role in propulsion, and if so, by how much.

This shouldn't be toooo hard to test, no? I mean we're talking about a graduate project here!

Furthermore, should also test with real riders too as frame stiffness may play a role in human fatigue, say in a 1-hr hard steady-state effort. This scenario is much harder to analyze, but still it'll give some insight into frame stiffness and human biomechanics and physiology.

I ask, if frame stiffness is all that important, at least that's what the manufacturers want us to believe, then why not just make a really super stiff frame from the get-go and call it a day. Why do manufactuers keep coming out with newer frames each year with ever so slightly increasing clamin in frame stiffness? Why not just make a super stiff frame from the get-go?? My bet is that those guys have already DONE the tests on frame stiffness and they in have the internal data to show that frame stiffness isn't all that important (compared to a huge other factors that goes into riding a bicycle) at this point the bicycle industry. But.. the marketing dept needs to bulletpoint their literature with "features", so the engineers will just need to make newer frames stiffer than the last (however slight and insignifcant that maybe), because after all, no Joe Weekend will want to buy a newer frame that is perceived as less stiff than his last frame, right?!

honestly, this thread as been one of the more interesting thread on RBR, but at the end of the day, it appears to be an academic reading, whose results/conclusions have very very little bearing in the real world. Why do I say this? Because in the real world, different levels of frame stiffness play an insignificant role in determing the outcomes of races. For the common Joe Weekend, the takeaway message of this thread should be: DON'T WORRY ABOUT FRAME STIFFNESS!


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## GlobalGuy (Jun 9, 2015)

aclinjury said:


> honestly, this thread as been one of the more interesting thread on RBR, but at the end of the day, it appears to be an academic reading, whose results/conclusions have very very little bearing in the real world.


If this thread was a fight someone would have stopped it days ago.


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## duriel (Oct 10, 2013)

So, stiff frames are faster, right?


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## tvad (Aug 31, 2003)

duriel said:


> So, stiff frames are faster, right?


Right.


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## velodog (Sep 26, 2007)

duriel said:


> So, stiff frames are faster, right?


Probably depends on who's riding it.


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## ibericb (Oct 28, 2014)

duriel said:


> So, stiff frames are faster, right?


than what?


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## tvad (Aug 31, 2003)

ibericb said:


> [faster] than what?


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## myhui (Aug 11, 2012)

aclinjury said:


> I ask, if frame stiffness is all that important, at least that's what the manufacturers want us to believe, then why not just make a really super stiff frame from the get-go and call it a day.


It's a trade off between frame stiffness and frame weight.

Every model year they present a new variation of that trade off.


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## Pirx (Aug 9, 2009)

aclinjury said:


> now measures the relevant data (speed, force) at both the crank and at the wheel.


Unfortunately, that's not good enough, since it will only give you a very small part of the story. The main question of how the metabolic cost for the rider changes can only be answered with a real rider. Many real riders, by the way, since you need decent statistics for a subject as fickle as a human being.



duriel said:


> So, stiff frames are faster, right?


Nope, wrong.


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## Z'mer (Oct 28, 2013)

Pirx said:


> That would be because _nobody_ knows. There are no published results, anywhere at all, that would demonstrate the claimed effect, or its opposite.
> 
> Well, sure, technically it is possible that someone has done the appropriate experiment, and has not told anyone about it. I would submit that that's quite an unlikely scenario.
> 
> Not to my knowledge, and I know a thing or two about the general subject, plus I know quite a few people who know the specific area of bicycle mechanics a lot better than I do.


The Josh Poertner's story about developing carbon wheels for Paris-Roubaix, linked early in this thread, shows the level of commitment companies go to with racing research. This is quite different from academic research. In most cases nothing gets published, results and methods are kept under lock and key. 

I expect people in charge at a pro racing level are aware of the BQ "planing" stuff, and as a minimum would have done something to check out the claims. You can't ignore those BQ claims for optimal frame stiffness / flex if you are looking for every edge to win.


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## Z'mer (Oct 28, 2013)

Pirx said:


> ...it is easy to describe ways to perform an experiment that would test the claims in question rigorously. For example, plop someone on an appropriate test bike (note that the term "appropriate test bike, however, already hides quite a bit of complexity), and measure both power output at the wheel and metabolic cost (say, via O2 consumption), and do so accurately. Of course, all of this is a lot easier said than done.


That's not the sort of experiment I had in mind. 
I would design an experiment to accurately show the results of the rider input. The bike makes no motion without a rider, so he is responsible for everything dynamic you measure. 

I would design this experiment with dynamic strain gauges on the frame, crank, and pedals, and a data acquisition system that synchronously samples them fast enough to capture the strain versus time. In this case, with a max crank speed of 2 Hz, at least 100 samples per second. 

Also it would capture the once per revolution reference of the crank, so all the strain data could be referenced correctly to crank position. It would fit in a backpack and be battery operated, so a rider could go out and ride normally for say an hour. 

The analysis of the data would be done in software using an existing package, either with typical x y plots, or if you wanted to be more fancy, operating deflection shape software designed for rotating machinery (that accepts a 1/rev phase reference pulse). 

I think Mark Richardson was one of the first to commercialize this type of software, one of his papers is 
http://www.systemplus.co.jp/support/data/techpaper/mescope/tech/32.pdf
his company 
ODS Animation - Vibrant Technology, Inc.

Of course, also record heart rate, power, speed, cadence and all the usual stuff we get as well. 
This would data acquisition would capture the actual frame movement versus a number of other variables like crank angle, instantaneous power, torque, pedal force (2 axis), etc. 

The goal of this experiment - to fully understand the relationship between frame flex and crankset torque. The only way the bike moves forward is when torque is generated at the crankset.


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## Z'mer (Oct 28, 2013)

Pirx said:


> P.S.: As an aside, those phase angle arguments that are brought up every now and then are largely misguided. Without going into the gory details, it is important to note that the phase angle of a parametrically excited second-order linear oscillator (which is what our bicycle frame is) follows from the excitation and its frequency, and is _not_ an independent variable. Attempting to prescribe both of these variables leads to an ill-posed problem. In short, the phase of the frame oscillations of a frame with no internal damping will adjust itself automatically such that the energy exchange becomes zero, on average. This does not directly address the question of conversion of frame internal energy into kinetic energy, but it is an important fact to keep in mind.


This seems to be the main difference of opinion between the analysis methods. 
Are you sure your model above, "parametrically excited second-order linear oscillator" is the correct model to use here? 

Again assume we are far below natural resonance.

What happens to that model if the mass is small, the maximum velocity is low, and the parametric driving force is large? 

There is a point where the momentum energy is totally swamped by the driving force energy, and may almost be ignored, the way you are ignoring damping. Or at least if not ignored, can be minor as compared to the driving force energy which now has almost total instantaneous control over any frame movement.


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## Pirx (Aug 9, 2009)

Z'mer said:


> I expect people in charge at a pro racing level are aware of the BQ "planing" stuff, and as a minimum would have done something to check out the claims. You can't ignore those BQ claims for optimal frame stiffness / flex if you are looking for every edge to win.


Well, what if there's nothing to that planning stuff? That's what I would expect. I hope you understand that this is my position, right?



Z'mer said:


> I would design this experiment with dynamic strain gauges on the frame, crank, and pedals, and a data acquisition system that synchronously samples them fast enough to capture the strain versus time. In this case, with a max crank speed of 2 Hz, at least 100 samples per second.


I don't know what "dynamic strain gauges" are. Strain gauges are strain gauges. You would have to explain what you expect to gain from those strain measurements. Without the ability to translate them into force data, those are entirely useless. Strain versus time alone does nothing for you.



Z'mer said:


> I think Mark Richardson was one of the first to commercialize this type of software,


The things you have described above this sentence are trivial to do with off-the-shelf software. Like I said, you still only have strain data at this point, which are of no use in and of themselves.



Z'mer said:


> Of course, also record heart rate, power, speed, cadence and all the usual stuff we get as well.
> This would data acquisition would capture the actual frame movement versus a number of other variables like crank angle, instantaneous power, torque, pedal force (2 axis), etc.
> 
> The goal of this experiment - to fully understand the relationship between frame flex and crankset torque. The only way the bike moves forward is when torque is generated at the crankset.


Heart rate is not a useful quantity for any of this since it depends on far too many additional parameters and is only vaguely related to power output. Power is of course crucial; once you have that, there's really no need to bother with speed or cadence.



Z'mer said:


> The goal of this experiment - to fully understand the relationship between frame flex and crankset torque.


Not good enough. You need to know how much power the rider's muscles exert to produce whatever it is you're measuring.


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## Pirx (Aug 9, 2009)

Z'mer said:


> This seems to be the main difference of opinion between the analysis methods.
> Are you sure your model above, "parametrically excited second-order linear oscillator" is the correct model to use here?


Yes, of course; that's not even a question.



Z'mer said:


> Again assume we are far below natural resonance.


Yep, sure.



Z'mer said:


> What happens to that model if the mass is small, the maximum velocity is low, and the parametric driving force is large?


Not sure what you're asking. That would be the case you expect for large stiffness. There's nothing special about that. Why would you think there could be an issue?



Z'mer said:


> There is a point where the momentum energy is totally swamped by the driving force energy, and may almost be ignored, the way you are ignoring damping.


Yes, and? That happens all the time for second-order systems of this kind; in the limit you'll end up with the quasi-stationary case and zero phase angle. Not very interesting, but nothing that the model or its differential equations have any problem handling, at all.



Z'mer said:


> Or at least if not ignored, can be minor as compared to the driving force energy which now has almost total instantaneous control over any frame movement.


That's a somewhat quaint way of describing what is happening, but sure. So what?


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## duriel (Oct 10, 2013)

Well, you'll want a follow vehicle taping the rider as the rider position will have a larger effect on the flexing of the frame than almost every other parameter. Is he standing? Pulling/not pulling on the bars? Is he sitting on the back of the seat and spinning? Is he sitting on the front of the seat and pressing? Is he wabbling all over the road or keeping it nice an tidy?


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## Z'mer (Oct 28, 2013)

Pirx said:


> Well, what if there's nothing to that planning stuff? That's what I would expect. I hope you understand that this is my position, right?
> 
> I don't know what "dynamic strain gauges" are. Strain gauges are strain gauges. You would have to explain what you expect to gain from those strain measurements. Without the ability to translate them into force data, those are entirely useless. Strain versus time alone does nothing for you.


I'm not sure what your position is at this point, besides "nobody knows". Maybe you can re-state it briefly if otherwise. 

Dynamic strain gauges are used for dynamic measurements, when the response bandwidth requires simultaneous sampling faster than, say, 1 Hz. 
And yes, there are different types of strain gauges which are dependent on the back end electronics in the acquisition system. 
Of course this was not meant to be a complete test procedure. 

You would need to calibrate them with a load cell first if you wanted strain versus force, or displacement if you wanted that versus force. 

But you could also use accelerometers and post process the data with double integration to get displacement or some other transducer if more convenient (if you only wanted relative frame displacement).


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## Pirx (Aug 9, 2009)

Z'mer said:


> You would need to calibrate them with a load cell first if you wanted strain versus force, or displacement if you wanted that versus force.
> 
> But you could also use accelerometers and post process the data with double integration to get displacement or some other transducer if more convenient (if you only wanted relative frame displacement).


Those are needlessly complex procedures for what we want to know. Given that we understand, and nobody, even in here, really disputes that material damping in the frame can be neglected all of this jazz, is really a royal waste of time. 

All you really want is an accurate measurement of power output at the wheel, which a powertap will do to about 1% (and you can probably do better with some fancy post processing of the data), and compare that to the physiological work put in by the rider. That part is hard, yes, but it's absolutely necessary. There is no way around that requirement.


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## Z'mer (Oct 28, 2013)

Pirx said:


> ..in the limit you'll end up with the quasi-stationary case and zero phase angle. Not very interesting, but nothing that the model or its differential equations have any problem handling, at all... So what?


The "so what" of when driving forces from pedals dominate momentum of the frame moving is you end up with 2 simple static equations to define the L and R pedal force influence on the frame, F = - k x. 

Where did the oscillator go? 

At the end of the day, you still have to convert pedal forced frame motion back to torque, and that seems to be an evasive area for you to discuss.
So think about this, for a though experiment. - You remove the L crank and turn it 180 so both cranks point down. Now have a friend lightly hold the the bike in the vertical balance position. If you apply force alternating on the L and R pedals, at normal cadence, you can flex and unflex the frame. You could do this at the same rate, and with the same force, as when pedaling the bike normally. 

But you would go nowhere. So even though you have a very similar motion of the frame, no torque is produced.
The frame can accept and give back energy, with no forward propulsion. To analyze propulsion you must know the crank angle when relevant forces are applied, as above there are crank angles where applied force = no propulsion. This can't be dismissed.


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## ibericb (Oct 28, 2014)

I've posed the question that follows previously in replies to others. So far nobody has suggested an answer, so let me try one last time here -- if we were to do whatever comparative measurement of rider input vs. output power at the rear wheel, and compare that between two frames of different stiffness to determine the performance differences of cyclist + bike, would we be concerned about differences in instantaneous power, or average power over a pedal cycle?


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## Pirx (Aug 9, 2009)

Z'mer said:


> The "so what" of when driving forces from pedals dominate momentum of the frame moving is you end up with 2 simple static equations to define the L and R pedal force influence on the frame, F = - k x.
> 
> Where did the oscillator go?


That's correct; like I said, you end up with the quasi-static case, the second derivative is gone, and the second-order differential equation becomes an algebraic equation. Again: So what? There's no singular behavior in this case, and the solutions transition smoothly. There's no issue.



Z'mer said:


> At the end of the day, you still have to convert pedal forced frame motion back to torque, and that seems to be an evasive area for you to discuss.


That's a misrepresentation, to put it mildly. Examples of mechanisms have been given and discussed, more than once, and otherwise the actual, exact details are obviously complex. I don't think too many people are even interested in those, other than as a case of academic curiosity. Once I know the input and output power, that's all I really care about.



Z'mer said:


> So think about this, for a though experiment. - You remove the L crank and turn it 180 so both cranks point down. Now have a friend lightly hold the the bike in the vertical balance position. If you apply force alternating on the L and R pedals, at normal cadence, you can flex and unflex the frame. You could do this at the same rate, and with the same force, as when pedaling the bike normally.


Fine, that's the popular Bowflex example. It doesn't apply. For reasons discussed before, _ad nauseam_.



Z'mer said:


> But you would go nowhere. So even though you have a very similar motion of the frame, no torque is produced.


No, the motion of the frame is not similar, at all, once we get back to realizing that we're talking about small effects in the first place. That means some care is necessary. Second, what is much more important here, is that the motion of the rider is _radically_ different. This is like saying that the efficiency of running of land animals must be close to zero, since the motion of the animal is "very similar" to simply hopping up and down, in which case the efficiency is zero.

This is important, mind you: The lesson from the above example is that simple analogies like the one you just proposed are completely, utterly worthless. It turns out that running of land animals, including kangaroos, is in fact amazingly efficient.



Z'mer said:


> The frame can accept and give back energy, with no forward propulsion. To analyze propulsion you must know the crank angle when relevant forces are applied, as above there are crank angles where applied force = no propulsion. This can't be dismissed.


The range of crank angles where no torque can be transmitted is exactly zero. In mathematics we call this a set of measure zero. In common language, it's irrelevant. A red herring.


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## Pirx (Aug 9, 2009)

ibericb said:


> would we be concerned about differences in instantaneous power, or average power over a pedal cycle?


I would mostly be concerned about differences in average power. The example of HFRoller that I discussed in some detail was looking at the long term effect of an initial transient, which indisputably exists. In that case there is a lasting difference (of a few inches total in a hard sprint over a couple of hundred yards). I had conceded that such a difference, while certainly small, might be of interest to someone racing professionally. Anyone can look at the numbers I gave and decide for themselves.


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## ibericb (Oct 28, 2014)

Pirx said:


> I would mostly be concerned about differences in average power. The example of HFRoller that I discussed in some detail was looking at the long term effect of an initial transient, which indisputably exists. In that case there is a lasting difference (of a few inches total in a hard sprint over a couple of hundred yards). I had conceded that such a difference, while certainly small, might be of interest to someone racing professionally. Anyone can look at the numbers I gave and decide for themselves.


That was my sense - that the performance difference would be reflected by average power. I say that without the rigor of proof, or any intent of pursuing it further. But, if indeed the net performance is reflected in average power developed over a cycle, or maybe total energy of such a cycle, then I can't see any of the arguments for increased power loss due to frame flex and spring energy storage vs return holding up on their own. It seems to me that any difference would have to derive from the resultant effect on the cyclist in torque application and the attendant angular velocity.


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## Z'mer (Oct 28, 2013)

Pirx said:


> I would mostly be concerned about differences in average power. The example of HFRoller that I discussed in some detail was looking at the long term effect of an initial transient, which indisputably exists. In that case there is a lasting difference (of a few inches total in a hard sprint over a couple of hundred yards). I had conceded that such a difference, while certainly small, might be of interest to someone racing professionally. Anyone can look at the numbers I gave and decide for themselves.


Really? Um, honestly I'm disappointed with this statement considering the assumptions in that model, and the discussion afterwards, etc. 
But, I guess summing the whole thing, this is the straw that breaks it for me...and leads to realization of what is going on here. Others had already pointed this out, my bad I had maintained a sliver of hope. Sorta like the last person to get the joke. Wow. 
Oh yeah, perhaps this comes to mind? 
https://www.youtube.com/watch?v=kQFKtI6gn9Y


----------



## Pirx (Aug 9, 2009)

That's a most perplexing reading of "what is going on here". The only way for me to explain such a mismatch between your perception and reality is to assume that you haven't understood a single word of what I said. I apologize for operating under the assumption that you did.


----------



## tvad (Aug 31, 2003)

Z'mer said:


> ...and leads to realization of what is going on here. Others had already pointed this out, my bad I had maintained a sliver of hope. Sorta like the last person to get the joke. Wow.
> Oh yeah, perhaps this comes to mind?
> https://www.youtube.com/watch?v=kQFKtI6gn9Y


Good to see the clouds broke and let the sunshine in. Great link!


----------



## aclinjury (Sep 12, 2011)

I think the important of stiffness is more marketing than substance.

Folks say that bicycle put all this R&D into making a frame stiff, and from that, we assume stiffness is pretty important, right? Well, Specialized worked with McLaren on the orginal Venge. Colnago worked Ferrari. Now, you must accept that when it comes for manipulating carbon fiber, McLaren and Ferrari are probably two of the best entities in the world in this field, agreed? Then why did McLaren and Ferrari not simply make the stiffest frame possible for the Venge and the Colnago bikes from the get go? As it turns out, the original McLaren Venge, which was released AFTER the Tarmac SL3, was in fact LESS stiff than the Tarmac SL3. And the Colnago bike is probably even less stiff than the Venge.

McLaren and Ferrari certainly would have the complete know-how to make an insanely stiff frame should they deem stiffness important.

Now, I can hear it now. Folks will say Specialized wanted to keep the Venge weight down, so that's why they compromise on stiffness. Bullsheet. The market for the buyers of the Venge are big guys looking to go fast on the flat or in a crit. Weight is absolutely not an issue here. Nobody weightweenie is going to buy a Venge looking to climb with it. So why didn't McLaren, with all their know-how, make the Venge stiffter than the SL3? Why? Perhaps McLaren know that stiffness beyond a certain point isn't all that important?? I think so. And btw, is the latest Venge even the stiffest frame on the market? No it is not. Again, if stiffness is all that, why isn't the latest Venge the stiffest frame on the market? I mean, the Venge is marketed to the flat and crit racing big boys, right? and if there's anything that these guys want, it's a "stiff" bike, right? So either McLaren doesn't have the know-how on how to make a stiff frame (unlikely!), or they already done the testing and realize stiffness isn't all what's crack up to be (likely).

I'm with Pirx on this one.


----------



## Jay Strongbow (May 8, 2010)

aclinjury said:


> I think the important of stiffness is more marketing than substance.
> 
> Folks say that bicycle put all this R&D into making a frame stiff, and from that, we assume stiffness is pretty important, right? Well, Specialized worked with McLaren on the orginal Venge. Colnago worked Ferrari. Now, you must accept that when it comes for manipulating carbon fiber, McLaren and Ferrari are probably two of the best entities in the world in this field, agreed? Then why did McLaren and Ferrari simply make the stiffest frame possible for the Venge and the Colnago bikes from the get go? As it turns out, the original McLaren Venge, which was released AFTER the Tarmac SL3, was in fact LESS stiff than the Tarmac SL3. And the Colnago bike is probably even less stiff than the Venge.
> 
> ...


Not really. They would have answered that they didn't want to make it so stiff that all comfort was lost.


----------



## aclinjury (Sep 12, 2011)

Jay Strongbow said:


> Not really. They would have answered that they didn't want to make it so stiff that all comfort was lost.


Waita minute. I thought carbon fiber was the gamechanger? What happen to all that talk about tuning the carbon layers and direction to make a frame stiff in one direction and comfortable in another direction?? I thought this was the magic property of carbon fiber? But let's assume that a stiff frame would be uncomfortable (we'd also be assume that McLaren wasn't able to tune the carbon fiber), well guess what, people who buy Venges are not the old guys looking for a comfort bike are they. People who buy Venge are the type who want to go fast on the flat at all cost; comfort takes a back seat. It's like nobody buys a Ferrari for comfort. So the comfort argument is not close, from many perspectives.

And let's also not forget that the orginal Venge, release AFTER the SL3, was in fact LESS stiff than the SL3. Makes no sense for McLaren to help Specialized build a frame meant for SPEED that is less stiff than what Specialized already had in stock, unless McLaren deemed that stiffness isn't all that?


----------



## Fireform (Dec 15, 2005)

Wow, nine pages and this is still going on.

Just for curiosity's sake, how does one reconcile this statement:


> If some of the energy input by the rider is used to temporarily flex the frame, once the frame un-flexes the energy is returned. All of it. No energy is lost. None. At. All.


With these statements:


Pirx said:


> Second, however, I will say that for a sprinter, even an advantage of an inch or two in a world championship may not be negligible, and my calculations show that a difference of an inch or so may be in the realm of what's possible to gain with a stiffer frame.
> 
> So, at the end of the day I think you do have a point that I will concede: In very hard sprint scenarios, there may indeed be a tiny benefit of frame stiffness. We need to keep in mind that in such a sprint scenario, many other variables come into effect as well. For example, the exact line that the rider chooses (or is forced to choose) will, over a distance of several hundred yards, typically lead to much larger differences in distance that the rider needs to travel than just an inch or two.


----------



## Pirx (Aug 9, 2009)

aclinjury said:


> Waita minute. I thought carbon fiber was the gamechanger? What happen to all that talk about tuning the carbon layers and direction to make a frame stiff in one direction and comfortable in another direction?? I thought this was the magic property of carbon fiber?


No, you're right on with this. End of discussion in that direction; there's no reason not to have a frame that's more laterally stiff without significantly affecting ride quality.

Also, earlier Z'mer had suggested that perhaps experiments had been done but were just not published. I'll just point out that this is utterly unbelievable. Just look at how various manufacturers peddle the power savings due to aerodynamics, or ceramic bearings, etc. Believe me, if there was any manufacturer who could demonstrate something along the lines of "_this frame saves you x Watts due to improved stiffness_", you would have seen such a claim by now. Indeed, the fact that no such specific claim has ever appeared in public anywhere, and all you ever see is some vague mumbling about "better power efficiency due to higher stiffness" that's never quantified in any way, shape or form, is as good an indication as any that no such results exist.


----------



## Pirx (Aug 9, 2009)

tvad said:


> Good to see the clouds broke and let the sunshine in. Great link!


Like I said, this discussion has a psychological dimension that's every bit as interesting as the physics. In any case, I hope this "sunshine" soothes your sleep, my poor friend.



Fireform said:


> Just for curiosity's sake, how does one reconcile this statement:
> [Frame flex does not dissipate energy, per se]
> 
> With these statements:
> [Transient effects are possible]


By following the discussion, perhaps, and understanding what was said, and what the effects in question are? Just a thought.


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## PBL450 (Apr 12, 2014)

Pirx said:


> No, you're right on with this. End of discussion in that direction; there's no reason not to have a frame that's more laterally stiff without significantly affecting ride quality.
> 
> Also, earlier Z'mer had suggested that perhaps experiments had been done but were just not published. I'll just point out that this is utterly unbelievable. Just look at how various manufacturers peddle the power savings due to aerodynamics, or ceramic bearings, etc. Believe me, if there was any manufacturer who could demonstrate something along the lines of "_this frame saves you x Watts due to improved stiffness_", you would have seen such a claim by now. Indeed, the fact that no such specific claim has ever appeared in public anywhere, and all you ever see is some vague mumbling about "better power efficiency due to higher stiffness" that's never quantified in any way, shape or form, is as good an indication as any that no such results exist.


Hmmm... Specialized will claim it soon it enough.


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## Pirx (Aug 9, 2009)

PBL450 said:


> Hmmm... Specialized will claim it soon it enough.


Well, yeah, but nobody with an ounce of good sense believes any of Specialized's numbers anyway, so they wouldn't count.


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## PBL450 (Apr 12, 2014)

Pirx said:


> Well, yeah, but nobody with an ounce of good sense believes any of Specialized's numbers anyway, so they wouldn't count.


Wait... I shaved my legs and saved over 2 minutes on a 20K TT? Haha... But I guess they get the advertising they want out of those ridiculous claims? Maybe they are geniuses? Put ridiculous numbers out there knowing it will get pop? Smart? I think it makes them look a little idiotic...


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## ibericb (Oct 28, 2014)

If you added up all the savings that SPecialized promises, you could finish a TT before the race even started.


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## aclinjury (Sep 12, 2011)

Pirx said:


> No, you're right on with this. End of discussion in that direction; there's no reason not to have a frame that's more laterally stiff without significantly affecting ride quality.
> 
> Also, earlier Z'mer had suggested that perhaps experiments had been done but were just not published. I'll just point out that this is utterly unbelievable. Just look at how various manufacturers peddle the power savings due to aerodynamics, or ceramic bearings, etc. Believe me, if there was any manufacturer who could demonstrate something along the lines of "_this frame saves you x Watts due to improved stiffness_", you would have seen such a claim by now. Indeed, the fact that no such specific claim has ever appeared in public anywhere, and all you ever see is some vague mumbling about "better power efficiency due to higher stiffness" that's never quantified in any way, shape or form, is as good an indication as any that no such results exist.


exactly. If people choose to believe that stiffness is as relevant as they think it is, and they believe that the bigs are putting in major R&D effort to make a frame stiff, then they must also accept the fact that McLaren and Ferrari are the 2 premiere players in the game of carbon fiber construction. And the fact that the bikes that were supposedly designed with the help from McLaren (Specialized) and Ferrari (Colnago) are NOT even the stiffest road bikes on the market, tells you that perhaps McLaren and Ferrari know that stiffness isn't all that. And like I said, the orginal Venge designed with the help from McLaren, and released after the SL3, was in fact less stiff than the SL3.

so.... did McLaren and Ferrari get it wrong by helping their partner design bikes that were not as stiff as they could be? The fact that 2 premier carbon fiber constructors in formula1 choose not to go with the stiffest frame possible,.. tell me they both unequivocally think it's not as important in the grand scheme of things when it comes to moving a bicycle forward. I think this is end of story for me. Thanks for the interesting discussion, Pirx.

Next time some dude says my ti frame is flexing and I'm losing power, I'll point him to this thread. hehe


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## Pirx (Aug 9, 2009)

aclinjury said:


> Next time some dude says my ti frame is flexing and I'm losing power, I'll point him to this thread. hehe


Bah, just drop the clown.


----------



## Lelandjt (Sep 11, 2008)

Velonews.com currently has tests of the Santa Cruz and Niner CX bikes that focus heavily on their lateral stiffness. It made me think of this thread.
I'm still on the side of wanting my frames to be as laterally and torsionally stiff as possible. For pedaling and handling.


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## Cinelli 82220 (Dec 2, 2010)

aclinjury said:


> McLaren and Ferrari are the 2 premiere players


Even they contract out some things.

This is a fun thread.


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## Pirx (Aug 9, 2009)

Lelandjt said:


> I'm still on the side of wanting my frames to be as laterally and torsionally stiff as possible. For pedaling and handling.


Absolutely nothing wrong with that. I have the same preference. 

I just don't think it matters for "power efficiency", and whether I am right or wrong in that belief has never been demonstrated.


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## froze (Sep 15, 2002)

I'm getting tired of this nonsense so these sites may answer some questions: 

Industry Standards part2 - Cervélo

https://janheine.wordpress.com/2013/02/19/laws-of-physics/

About frame stiffness ? what is stiff? Velocite Bikes blog, news and updates | Velocite Bikes blog, news and updates


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## davidka (Dec 12, 2001)

aclinjury said:


> , then they must also accept the fact that McLaren and Ferrari are the 2 premiere players in the game of carbon fiber construction.


I do not accept that, at all. I would bet my bikes that the top bike makers have more carbon structure expertise than either of those auto makers. Having examined carbon fiber aircraft structures compared to unfinished bike frames I could plainly see how much more advanced the bicycle frame was. Larger structures simply cannot be molded with the same sophisticated methods that smaller ones can.

The McLaren and Ferrari relationships are purely marketing.


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## stevesbike (Jun 3, 2002)

Pirx said:


> Blah blah blah. You know, Steve, I highly recommend you just stay out of this. By now it is clear to everyone, but absolutely every single person having followed this thread, that you have exactly zero to contribute. But, by all means, if you enjoy making a fool of yourself, carry on.


I haven't responded to you for a few weeks because I actually feel sorry for you. You seem to have some narcissistic pathology that derives some satisfaction from feeling as though people actually care what you think. It's an internet forum. No one cares what you think. You seem to think that insulting other people will elevate your status, but I can guarantee you that my scientific credentials vastly exceed yours. If you have anything interesting to add to this debate, please provide it. Otherwise, you've begun by citing the most discredited "study" in cycling science, offered not an iota of insight, and have apparently nothing to contribute to this debate. But glad that the forum serves as a mechanism of self-medication for you. You encapsulate just about everything that is wrong with anonymous forums. Sad.


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## Pirx (Aug 9, 2009)

Hi Steve. Long time no see. So, how have you been?



> Sad.


I'm sorry.


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## Lelandjt (Sep 11, 2008)

stevesbike said:


> I haven't responded to you for a few weeks because I actually feel sorry for you. You seem to have some narcissistic pathology that derives some satisfaction from feeling as though people actually care what you think. It's an internet forum. No one cares what you think. You seem to think that insulting other people will elevate your status, but I can guarantee you that my scientific credentials vastly exceed yours. If you have anything interesting to add to this debate, please provide it. Otherwise, you've begun by citing the most discredited "study" in cycling science, offered not an iota of insight, and have apparently nothing to contribute to this debate. But glad that the forum serves as a mechanism of self-medication for you. You encapsulate just about everything that is wrong with anonymous forums. Sad.


Burn!


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## Lelandjt (Sep 11, 2008)

Pirx said:


> Hi Steve. Long time no see. So, how have you been?
> 
> 
> 
> I'm sorry.


Zing!


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## froze (Sep 15, 2002)

I don't know why but whenever I come to this thread this song pops up into my head: 

CHUCK BERRY LYRICS - My Ding A Ling


----------



## goodboyr (Apr 19, 2006)

For me, its this:

https://youtu.be/9wWUc8BZgWE


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## robt57 (Jul 23, 2011)

goodboyr said:


> For me, its this:
> 
> https://youtu.be/9wWUc8BZgWE



Bingo!

"Aren't you ashamed to pontificate like that" 

Which could read "You 'should be' ashamed to pontificate like that".

But everybody expresses themselves differently. I won't rule out that, in this case, the pontificating subject might just be someone whom could or would have your back as a friend. Just limit the keyboard rights for Pete's sake.  An anti pontification proxy server or something? :idea:


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## Pirx (Aug 9, 2009)

froze said:


> I don't know why [...]


Neither do I. You probably haven't read the thread.

I will submit that in general, people dissing this thread probably haven't read through it in sufficient depth; not that I blame them, it's long, and contains a number of pieces that aren't exactly the kind of light fare you usually see around here plus, yes, quite a bit of nonsense, too. Oh well.


----------



## Doug B (Sep 11, 2009)

Pirx said:


> Well, yeah, I'm strange this way I know. I'm one of those weird people who thinks that the laws of physics do hold. There are others, like you, who feel their imagination trumps physics. That's what is indeed required to believe in the fairytales of the miraculous benefits of frame stiffness.
> 
> 
> 
> ...


Actually, I'm certain a tiny bit of energy is in fact lost....it gets converted to heat as the frame flexes back and forth. However, for this discussion, it is most likely negligible.


----------



## thumper8888 (Apr 7, 2009)

Pirx said:


> If some of the energy input by the rider is used to temporarily flex the frame, once the frame un-flexes the energy is returned. All of it. No energy is lost. None. At. All.



Not true. This is the place the physics of it start, at least for esoteric discussions like this. But it's more complex. 
Here is some, mind you, just SOME of the fine print.
There will be heat loss. You won't feel the frame warming up, but it happens. 
And the flex would have to be in the drive train to go directly into propulsive force when a "spring" springs back. But instead the energy used to bend the frame laterally, is just returned by the frame unbending in the other direction. Perhaps when your pedal on that side is de-weighted.
In short, what you're talking about is frame bending back and forth, not the crankset bending fore-to-aft.
And even then, if you bent a crank arm with forward propulsive force, the return may do little more than unbend the arm at a point in the pedal stroke where much of the force doesn't go into the force propelling the bike forward.
If noodley frames were faster, the pro tour would be on a noodley frame.
Cavendish, for example, can ride whatever he pleases, as he has repeatedly shown, and will go to anything length to squeeze another fraction of a watt of forward energy out of his springs.
He's stayed on stiff frames.
Keep at it though. This is half a step away from inventing perpetual motion.


----------



## Pirx (Aug 9, 2009)

You would have benefitted from reading what has been posted in this thread, you know, like a couple of hundred posts back, rather than responding to Post #8 while ignoring the 460+ posts that came after that one. Long, _long_ story short, your response is some really old hat, and has been discussed _ad nauseam_ before. As one might expect.


----------



## thumper8888 (Apr 7, 2009)

Pirx said:


> As one might expect.


Perhaps you would enlighten me on this point? I'm a little dimwitted, and perhaps it's an insinuation about that.
I skimmed it all. There is a huge volume of N=1, a bunch of subjective comments, a bunch of the usual steel bike fanboy stuff, and at least SOME real science, albeit from god help us Schwinn, that well-known fount of hard science... albeit based on the ever-fallible FEA. 
Oh, and there were some great bunny rabbit photos.
I didn't see any reasonable explanation as to why essentially every last single person who makes a living off road and TT is running pretty much the stiffest thing they kind find. And this includes at least some people who aren't sponsored by bike companies.


----------



## goodboyr (Apr 19, 2006)

There's just not enough popcorn in the world........


----------



## robt57 (Jul 23, 2011)

goodboyr said:


> There's just not enough popcorn in the world........


No doubt about it. . .


----------



## thumper8888 (Apr 7, 2009)

robt57 said:


> No doubt about it. . .


Uh-oh. You boys are scaring me now.
Just calling it like it is, not making anything personal. NOTHING. Goodboyr, seems like you made good points in that regard in the past and I've tried to take them to heart.
The subjective part of this could go on forever without settling anything. My question about the pro peloton and other pro riders is sincere.


----------



## ibericb (Oct 28, 2014)

thumper8888 said:


> ...My question about the pro peloton and other pro riders is sincere.


Those guys are limited to a choice within the models supplied by the bike sponsor. They don't get to do much shopping, and they don't get anything you can't buy from the same manufacturer (i.e., it's their frames aren't customized).


----------



## tvad (Aug 31, 2003)

goodboyr said:


> There's just not enough popcorn in the world........


My thought exactly.


----------



## tvad (Aug 31, 2003)

ibericb said:


> ...they don't get anything you can't buy from the same manufacturer (i.e., it's their frames aren't customized).


That's simply incorrect.

From the Sarto website:



> Presently, Sarto's frames are being ridden by top pro tour riders whose identity cannot be disclosed for the protection of the sponsoring companies whose paint jobs clothe Sarto's frames.


You will find similar language on the Legend website. Marco Bertoletti once worked for Sarto, and now owns his own bike company, Legend. Both builders manufacture custom frames for pro tour riders.


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## goodboyr (Apr 19, 2006)

thumper8888 said:


> Uh-oh. You boys are scaring me now.
> Just calling it like it is, not making anything personal. NOTHING. Goodboyr, seems like you made good points in that regard in the past and I've tried to take them to heart.
> The subjective part of this could go on forever without settling anything. My question about the pro peloton and other pro riders is sincere.


Yup. I'm not thinking its going to get personal. Just thinking the discussion is now repetitive. But I'm no moderator, so have at it..........


----------



## Jwiffle (Mar 18, 2005)

tvad said:


> That's simply incorrect.
> 
> From the Sarto website:
> 
> ...


It used to be common for pros to have a bike made by someone other than the sponsor. Don't think that is able to happen anymore, since the uci has mandated frames first be approved by them, as well as anything used in competition be available to the public within 6 months from first being used. (Might be wrong about 6 months, maybe it's a year, but no matter). In other words, pros are mostly stuck to stock frames now.


----------



## tvad (Aug 31, 2003)

Jwiffle said:


> It used to be common for pros to have a bike made by someone other than the sponsor. Don't think that is able to happen anymore, since the uci has mandated frames first be approved by them, as well as anything used in competition be available to the public within 6 months from first being used. (Might be wrong about 6 months, maybe it's a year, but no matter). In other words, pros are mostly stuck to stock frames now.


So, you're saying Sarto is lying on their website?

Why could UCI not inspect and approve a custom frame upon receipt of the design and prototype?

Any of Sarto or Legend's frame models are available immediately for order. No need to wait 6 months. There's nothing special about a custom frame made for a pro peloton rider other than geometry and perhaps a custom mix of tubes to tune the ride performance. They just paint the frames to match the team bikes. The tube sets are all available to anyone who wants to order a custom frame from Sarto or Legend.


----------



## Jwiffle (Mar 18, 2005)

tvad said:


> So, you're saying Sarto is lying on their website?
> 
> Why could UCI not inspect and approve a custom frame?
> 
> Any of Sarto or Legend's frames are available immediately for order. No need to wait 6 months. There's nothing special about a custom frame made for a pro peloton rider other than geometry. They just paint them to match the team bikes. The tube sets are all available to anyone who wants to order a custom frame from Sarto or Legend.


I didn't say it was impossible that some pros are riding custom frames, but I guarantee you that it is much less common than it once was. The custom builder would have to pay for the frame to go through the approval process. It's not cheap, and probably not worth it for a single frame.


----------



## tvad (Aug 31, 2003)

Jwiffle said:


> I didn't say it was impossible that some pros are riding custom frames...


You absolutely implied it.

You wrote:


> Don't think that is able to happen anymore...


You agree that it's possible that some riders are riding custom frames. 

Good. That was my only point. 

Sarto and Legend aren't getting approval for one custom frame. They are getting approval for a frame model in their production line. That's what UCI requires. Not so unrealistic.


----------



## Jwiffle (Mar 18, 2005)

tvad said:


> You absolutely implied it.
> 
> You wrote:
> 
> ...


Yeah, I guess I did imply it. Maybe it does happen, but it must be rare. There seemed to have been more pressure from sponsors over the last several years for riders to ride their bikes, and now with the approval process in place by the uci, it seems harder for a one-off to happen. Also, pretty much every review of a pro's bike I read in any magazine anymore points out he's using a stock bike and not a one-off.

So which pros aren't using their sponsor's bikes?


----------



## Pirx (Aug 9, 2009)

goodboyr said:


> Just thinking the discussion is now repetitive.


Yep, that's the main point. Someone comes up with something original, which hasn't been addressed a half dozen times at least before, I'll be happy to address. Otherwise I'll refuse to keep going over the same old ground over and over again. But, hey, maybe this is the immortal (or undead?) thread, and if someone or other wants to keep it going forever, then that's perfectly fine, too.

Just to briefly reiterate the point: There may be, and probably are, plenty of reasons to like (laterally) stiff frames. The specific question _here_ was whether there's any measurable, quantifiable benefits with respect to "power efficiency", "power transfer" or anything along those lines, which could translate into better overall performance. The answer is that nobody has ever demonstrated any such effects in the real world.


----------



## tvad (Aug 31, 2003)

Jwiffle said:


> So which pros aren't using their sponsor's bikes?


They are prevented from stating whom.



> Presently, Sarto's frames are being ridden by top pro tour riders *whose identity cannot be disclosed for the protection of the sponsoring companies* whose paint jobs clothe Sarto's frames.


----------



## ibericb (Oct 28, 2014)

tvad said:


> That's simply incorrect.
> 
> From the Sarto website:
> 
> ...


You need to familiarize yourself with current UCI regulations on equipment that can now be used in competition. The exact same equipment, including frames, must be available to the public within 9 months of being used in competition, and before it can be used it must be announced, including when it will be available. Custom frames are a thing of the past - no longer allowed.


----------



## tvad (Aug 31, 2003)

ibericb said:


> You need to familiarize yourself with current UCI regulations on equipment that can now be used in competition.


I did. I read the Protocol front to back earlier today. It says nothing about excluding custom frames. Perhaps you need to read it more carefully yourself.

As I stated, custom Sarto and Legend frame models used by pros are are available to the public _now_...never mind 9 months from use in competition.

Look, this isn't worth debating for me anymore. It comes down to whether one believes Sarto and Legend are being truthful on their websites or not (and reviewers are being truthful in their reviews). I believe they are. Several of you believe they aren't. So be it.

This sidebar has nothing to do with the topic.


----------



## ibericb (Oct 28, 2014)

If it's available to the public, then it is hardly "custom".


----------



## tvad (Aug 31, 2003)

ibericb said:


> If it's available to the public, then it is hardly "custom".


Good God. You can't be serious. 

Are you familiar with the concept of a custom frame? How about a bespoke suit? Available to the public, yes? Yes.

Anyone can contact the company, or a bike shop in the USA that represents Sarto, place an order and buy one.

You want a custom, i.e. made-to-measure, Sarto SETA? No problem. It has a specific tube set for this model. Other Sarto models have different tube sets. Choose your model. Place an order. Make a deposit. Send in your sizes from a custom fitting session, and it's built to your measurements and painted however you want it painted.

Same thing done for pros. Custom sizing. Custom painting. Done.


----------



## ibericb (Oct 28, 2014)

tvad said:


> I did. I read the Protocol front to back earlier today. It says nothing about excluding custom frames. Perhaps you need to read it more carefully yourself. ...


So let me add, from the UCI document _Clarification Guide of the UCI Technical Regulation_, page 5:


*Article 1.3.007*:
_“Bicycles and their accessories shall be of a type that is sold for use by anyone practising cycling as a sport. As a result of production imperatives (time constraints), an exception may be requested from the UCI for equipment that is a final product and that will be marketed in the nine months after its first use in competition. The manufacturer must however publish information on the equipment in question in advance and announce the date of its market launch. The use of equipment designed especially for the attainment of a particular performance (record or other) shall be not authorised.”_​
Then the following clarification:

_The bicycle must be accessible to all participants. All the components of the bicycle must be available commercially (i.e. available on the market or sold directly by the manufacturer) at the latest nine months after their first use in competition. To implement this nine-month period, the manufacturer must publicly announce that the product in question is being used in competition and when it will be available for sale. In all cases the product must be a finished product in the condition that it will be marketed. The testing of a prototype in competition is prohibited.

Thus, it is not allowed to use equipment in competition that is not either available on the market or previously communicated by the manufacturer (with a nine months period for the marketing).

*Prototypes and the use of equipment specially designed for a particular athlete, event or performance are prohibited. *"Specially designed" means a bicycle with a technical added value when compared with other equipment.

No minimum production quantity or minimum price is defined for either bicycles or any component parts._​
Seems pretty clear to me - _the use of equipment specially *designed for a particular athlete*, event or performance are prohibited_.

What am I missing?


----------



## ibericb (Oct 28, 2014)

see my added reply

size and paint aren't the issue - it's about stiffness, remember?


----------



## tvad (Aug 31, 2003)

ibericb said:


> *Prototypes and the use of equipment specially designed for a particular athlete, event or performance are prohibited. *"Specially designed" means a bicycle with a technical added value when compared with other equipment.


Sarto and Legend bicycles are not _designed for a specific athlete_. In fact, their models are designed for all athletes. The only difference is the made-to-measure geometry of the frame. 



> "Specially designed" means a bicycle *with a technical added value when compared with other equipment.*


They do not provide any special design with _technical added value when compared to other equipment_ unless you count a great fitting made-to-measure frame as a special added technical benefit, which I am certain you will agree is not the spirit of the UCI guildeline.

Again, essentially you believe Sarto and Legend are lying on their websites. If you want to take them to task for what they claim, then contact them directly.


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## ibericb (Oct 28, 2014)

tvad said:


> They do not provide any special design with _technical added value when compared to other equipment_ unless you count a great fitting made-to-measure frame as a special added technical benefit, which I am certain you will agree is not the spirit of the UCI guildeline.


Prexactly! 

So - to stay on topic - regarding frame stiffness, it isn't custom, or unique. It's available to everyone. Sizing isn't the issue (so long as anyone could order the exact same size and geometry) - it's about unique performance ability. That's specifically prohibited.


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## tvad (Aug 31, 2003)

ibericb said:


> Prexactly!
> 
> So - to stay on topic - regarding frame stiffness, it isn't custom, or unique. It's available to everyone. Sizing isn't the issue (so long as anyone could order the exact same size and geometry) - it's about unique performance ability. That's specifically prohibited.


Right! So, what the hell are we debating? Sarto and Legend build bikes for some pros in the Pro Peloton. It has not a damn thing to do with the stiffness of the frames (and I never claimed it did). 

It has everything to do with made-to-measure frame sizing, and it doesn't change the fact that Sarto and Legend supply custom frames.


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## ibericb (Oct 28, 2014)

tvad said:


> Right! So, what the hell are we debating? Sarto and Legend build bikes for some pros in the Pro Peloton. It has not a damn thing to do with the stiffness of the frames (and I never claimed it did).
> 
> It has everything to do with made-to-measure frame sizing, and it doesn't change the fact that Sarto and Legend supply custom frames.


It was about what pro's ride to get an advantage, which was related to frame stiffness. In that vain custom sizing (or paint) isn't "custom", or one-off, or unique, any more than individual fitting is. They enjoy the same frame stiffness as the next guy on the same make, model and size (which must be available to all). That was the issue.


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## tvad (Aug 31, 2003)

ibericb said:


> It was about what pro's ride to get an advantage, which was related to frame stiffness. In that vain custom sizing (or paint) isn't "custom", or one-off, or unique, any more than individual fitting is. They enjoy the same frame stiffness as the next guy on the same make, model and size (which must be available to all). That was the issue.


There are some people for whom off-the-shelf frames cannot be made to fit properly no matter the stems installed or the saddles adjusted.

That's precisely why a pro would order a custom frame. _A well fitting frame offers a definite advantage for those who need it._

BTW...you did not specify stiffness as a characteristic of customization in post #479:


> Those guys are limited to a choice within the models supplied by the bike sponsor. They don't get to do much shopping, and they don't get anything you can't buy from the same manufacturer (i.e., it's their frames aren't customized).


Had you done so, I would not have replied with a correction to your statement.


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## thumper8888 (Apr 7, 2009)

Jwiffle said:


> I didn't say it was impossible that some pros are riding custom frames, but I guarantee you that it is much less common than it once was. The custom builder would have to pay for the frame to go through the approval process. It's not cheap, and probably not worth it for a single frame.


I was at one point pondering the purchase of a bike that Cavendish rode in Paris-Roubaix, and in theory it was a Specialized "Roubaix."
Hard rubber inserts, the works. Except... the head tube measured out shorter than a Tarmac's. 
Now, that was somehow allowed. But it is also one hell of a lot more customized than many, many "custom" frames.
Did they go into the layup and take out 30 grams of medium mod and replace it with a 6 grams better-oriented hi-mod unidirectional here, and two grams there? Dunno. But UCI would never, ever be able to figure it out if they had. Margin of manufacturing tolerance blah blah blah.
Then there was the case of one or two sl-4 Tarmacs in the peloton with tiny McLaren stickers. Not the newer model that was sold to the public. The previous model. That sticker pretty much guaranteed some carefully oriented high-mod.
And those are just things I know about, and I'm nobody....Clearly "custom" and "UCI legal" are in the eyes of the beholder and really aren't part of this argument.
What is true, is that no matter how much for debate purposes someone might want to insist that the pros are stuck with manufacturers' choices, they aren't.
There is no way that strong-willed people like Cancellara, Wiggins and Cavendish are going to settle for bikes that they think are slower than a wiggly one. Nor would manufacturers miss a chance to make a buck. There would be a new line of bikes tomorrow built by Specialized and sold via their patented semi-scientific marketing blather, which would explain in painful, chart-and-win-tunnel detail, how the S-Works Flacidity is 127 seconds faster over a 40k time trial than the competing hyper-rigid Giant Priapism.


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## Jwiffle (Mar 18, 2005)

thumper8888 said:


> I was at one point pondering the purchase of a bike that Cavendish rode in Paris-Roubaix, and in theory it was a Specialized "Roubaix."
> Hard rubber inserts, the works. Except... the head tube measured out shorter than a Tarmac's.
> Now, that was somehow allowed. But it is also one hell of a lot more customized than many, many "custom" frames.
> Did they go into the layup and take out 30 grams of medium mod and replace it with a 6 grams better-oriented hi-mod unidirectional here, and two grams there? Dunno. But UCI would never, ever be able to figure it out if they had. Margin of manufacturing tolerance blah blah blah.
> ...


Well, maybe I'm wrong about pros getting one-off bikes. But if it's mainly for geometry and preferred fit, I'm now wondering how we got off topic. As stiff as today's stock frames are, it's not like they need to go custom to get a stiffer bottom bracket.


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## davidka (Dec 12, 2001)

thumper8888 said:


> The subjective part of this could go on forever without settling anything. My question about the pro peloton and other pro riders is sincere.


They seek stiff because they are just as subjective to marketing as we are, ie. they have been told what they need. Pros, for the most part, aren't equipment experts. If you look at the way some of the successful riders out there fit their bikes, it's obvious.

And yes, Sarto is lying about their bikes being use in the Pro Tour. Here is the 2014 list of approved frames. Notice Sarto's absence:

https://www.google.com/url?sa=t&sou...KdrNlIESAymViJ3gQ&sig2=R_WUYlQWnnK1MvPXNiDIBw


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## ibericb (Oct 28, 2014)

There are team issue versions, but they must be available to the public. For example, compare the geometry of the standard Trek Domane to the Domane Limited Koppenberg Edition frames. The latter is Cancellara's Domane. You can buy the exact same frame, and have it finished as a P1 bike if you wish, same price as a 6 series Domane frame. It's not custom (other than paint), or one-off, but it is very different than the standard, ordinary retail Domane. You just need to know exactly what to look for. If they ride it in the pro peloton, you can buy and ride it too.


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## tvad (Aug 31, 2003)

davidka said:


> And yes, Sarto is lying about their bikes being use in the Pro Tour. Here is the 2014 list of approved frames. Notice Sarto's absence:
> 
> https://www.google.com/url?sa=t&sou...KdrNlIESAymViJ3gQ&sig2=R_WUYlQWnnK1MvPXNiDIBw


I believe they are telling the truth. They specifically explain why you do not see them on the list. 

Bottom line, it doesn't really matter to this discussion.


----------



## Jackhammer (Sep 23, 2014)

Pirx said:


> Yep, that's the main point. Someone comes up with something original, which hasn't been addressed a half dozen times at least before, I'll be happy to address. Otherwise I'll refuse to keep going over the same old ground over and over again. But, hey, maybe this is the immortal (or undead?) thread, and if someone or other wants to keep it going forever, then that's perfectly fine, too.
> 
> Just to briefly reiterate the point: There may be, and probably are, plenty of reasons to like (laterally) stiff frames. The specific question _here_ was whether there's any measurable, quantifiable benefits with respect to "power efficiency", "power transfer" or anything along those lines, which could translate into better overall performance. The answer is that nobody has ever demonstrated any such effects in the real world.


*Not everything that can be counted counts.
** Not everything that counts can be counted. Einstein
*
There's also sensitive dependence on initial conditions.

Tiny differences in input can make tremendous differences in output, so it goes to follow that differences in stiffness can have small but meaningful effects in performance...


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## Pirx (Aug 9, 2009)

thumper8888 said:


> Nor would manufacturers miss a chance to make a buck. There would be a new line of bikes tomorrow built by Specialized and sold via their patented semi-scientific marketing blather, which would explain in painful, chart-and-win-tunnel detail, how the S-Works Flacidity is 127 seconds faster over a 40k time trial than the competing hyper-rigid Giant Priapism.


Hmm, you would think so, now, wouldn't you? So, how do you explain the fact that no publication exists, anywhere, wherein it would be explained in "painful, chart-and-wind-tunnel detail", how the S-Works Rigidity is 0.127 seconds faster over a 400k time trial than the competing hyper-flexy Giant Noodility? Why, might that be because perhaps no such results exist? Noooo, that can't be, or can it?

P.S.: I will refrain from even going into the utter ludicrousness of the idea that a couple of pieces of this-or-that carbon here or there, oriented this way or that way, would make one wit of a difference.


----------



## Pirx (Aug 9, 2009)

Jackhammer said:


> *Not everything that can be counted counts.
> ** Not everything that counts can be counted. Einstein
> *
> There's also sensitive dependence on initial conditions.
> ...


Oh please, for the love of god... Do yourself a favor and refrain from talking about things you don't understand. There are no positive Lyapunov exponents in the dynamical system we are discussing here.

The Einstein quote you gave does have some relevance, however: Yes, there are consequences of frame stiffness that can and do lead people to prefer such frames, even if there are no quantifiable performance benefits, and that's perfectly fine. Lots of people like red bikes better than blue ones, too. Or vice versa. That's different, however, since everyone knows that red bikes are faster.


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## robt57 (Jul 23, 2011)

Jackhammer said:


> *Not everything that can be counted counts.
> ** Not everything that counts can be counted. Einstein
> *


Did you say.... Count?


----------



## Jackhammer (Sep 23, 2014)

Pirx said:


> Oh please, for the love of god... Do yourself a favor and refrain from talking about things you don't understand. There are no positive Lyapunov exponents in the dynamical system we are discussing here.
> 
> The Einstein quote you gave does have some relevance, however: Yes, there are consequences of frame stiffness that can and do lead people to prefer such frames, even if there are no quantifiable performance benefits, and that's perfectly fine. Lots of people like red bikes better than blue ones, too. Or vice versa. That's different, however, since everyone knows that red bikes are faster.


Dude, I generally agree with your ad nauseam bs spewing here. 

But, you just made it clear with your take on the Einstein quote that you have problems deciphering plain English.

Give your head a shake, read it again, and then we can talk about Lyapunov exponents to your hearts content.

Fatigue influences the dynamic stability of the torso. - PubMed - NCBI


----------



## Pirx (Aug 9, 2009)

Jackhammer said:


> But, you just made it clear with your take on the Einstein quote that you have problems deciphering plain English.


Ahh, now you've got my attention. By now English and its grammar and spelling have become more interesting than the discussion of frame properties in this thread. So, would you humor me and explain what you think is wrong with what you have identified as my take on the Einstein quote? I'm truly interested. Oh, and dude, note that I was agreeing with your take on Einstein's quote... 

Alternatively, feel free to explain the relevance of those finite-time Lyapunov exponents for this discussion. :devil:


----------



## Jackhammer (Sep 23, 2014)

Pirx said:


> Ahh, now you've got my attention. By now English and its grammar and spelling have become more interesting than the discussion of frame properties in this thread. So, would you humor me and explain what you think is wrong with what you have identified as my take on the Einstein quote? I'm truly interested. Oh, and dude, note that I was agreeing with your take on Einstein's quote...
> 
> Alternatively, feel free to explain the relevance of those finite-time Lyapunov exponents for this discussion. :devil:


I'll do both.

Define quantifiable.

Then read this
Fatigue influences the dynamic stability of the torso. - PubMed - NCBI


----------



## Jackhammer (Sep 23, 2014)

Pirx said:


> Oh please, for the love of god... Do yourself a favor and refrain from talking about things you don't understand. There are no positive Lyapunov exponents in the dynamical system we are discussing here.


Really?

HKUL: Electronic Resources

The results found positive Lyapunov exponent and fractional Kaplan-Yorke dimension values in each muscle for each trial of each posture. The study concluded the existence of chaotic behavior in upper extremity muscles during static task conditions.


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## Jackhammer (Sep 23, 2014)

Pirx said:


> Oh please, for the love of god... Do yourself a favor and refrain from talking about things you don't understand. *There are no positive Lyapunov exponents in the dynamical system we are discussing here.
> *


Furthermore,

High odds ratios of Lyapunov exponent and Kaplan-Yorke dimension led to the conclusion that the nonlinear properties of the muscles could explain muscle fatigue.

Maybe this has some relevance to disproving your rant?? LOL

I'll give you some more hints tomorrow!! Ha!


----------



## Pirx (Aug 9, 2009)

Jackhammer said:


> I'll give you some more hints tomorrow!! Ha!


Yes, I love riddles. Give me more hints, please. 

No seriously, please stop it, you're killing me. On a serious note, stuff of the kind you linked to is, by and large, BS. But this is so far off-topic here it's not even funny, so I'm not going any further down this road.


----------



## goodboyr (Apr 19, 2006)

Please change the title of this thread to something more representative. My suggestion "Duelling Roadbikereview Banjos". 
Amazing! I go to sleep and wake up the next morning to find 5 more pages of posts and not one has to do with stiffness. This thread is gold!


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## ibericb (Oct 28, 2014)

tvad said:


> Bottom line, it doesn't really matter to this discussion.


Well, then why did you make it an issue?

If Sarto and Legend are making frames used in the pro peloton as we know it today, then either:

1. they are a contract manufacturer for a recognized and approved make and model, and you can buy the exact same frame, geometry, size, etc. from the identified manufacturer, under the same brand identity, etc.

or

2. their admitting to cheaters using their bikes, and aiding them in doing so.

So, which is it?


----------



## Pirx (Aug 9, 2009)

goodboyr said:


> Please change the title of this thread to something more representative. My suggestion "Duelling Roadbikereview Banjos".
> Amazing! I go to sleep and wake up the next morning to find 5 more pages of posts and not one has to do with stiffness. This thread is gold!


Yeah, it truly has become the thread that keeps on giving. You're right, nobody is interested in the frame stiffness question anymore. That's quite fitting, since we have established that frame stiffness doesn't matter. :devil:


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## tvad (Aug 31, 2003)

ibericb said:


> Well, then why did you make it an issue?


That has been covered earlier. Do a review.

Moving on. 

Nice day here in Southern California. Sunny and low 70s.


----------



## Jackhammer (Sep 23, 2014)

*Ok*



Pirx said:


> Ahh, now you've got my attention. By now English and its grammar and spelling have become more interesting than the discussion of frame properties in this thread. So, would you humor me and explain what you think is wrong with what you have identified as my take on the Einstein quote? I'm truly interested. Oh, and dude, note that I was agreeing with your take on Einstein's quote...
> 
> Alternatively, feel free to explain the relevance of those finite-time Lyapunov exponents for this discussion. :devil:


Tracking Muscle Fatigue Markers Through Nonlinear and Multivariate Analysis of Motion Kinematics | David Chelidze - Academia.edu


----------



## Jackhammer (Sep 23, 2014)

Pirx said:


> Yes, I love riddles. Give me more hints, please.
> 
> No seriously, please stop it, you're killing me. On a serious note, stuff of the kind you linked to is, by and large, BS. But this is so far off-topic here it's not even funny, so I'm not going any further down this road.


You're not going down this road anymore because you've inadvertently undermined your own assertions about stiffness being a fairytale. 

Maybe you should focus more on the chaos of muscular fatigue in conjunction with frame stiffness rather than soley on the mechanics of bicycles?


----------



## Pirx (Aug 9, 2009)

Jackhammer said:


> You're not going down this road anymore because you've inadvertently undermined your own assertions about stiffness being a fairytale.


Sure, sure. Not biting unless you have something of substance to say. Random web links won't do the trick, sorry. Come back if you can construct a cogent argument, or point to a cogent argument anywhere in the literature, that would link these Lyapunov exponents to elastic properties of frames. Without that, all you have is random noise.


----------



## Jackhammer (Sep 23, 2014)

Pirx said:


> Sure, sure. Not biting unless you have something of substance to say. Random web links won't do the trick, sorry. Come back if you can construct a cogent argument, or point to a cogent argument anywhere in the literature, that would link these Lyapunov exponents to elastic properties of frames. Without that, all you have is random noise.


So you acknowledge that Lyapunov exponents exist in the bicycle/rider system?

Before you mocked me and said they did not.


----------



## stevesbike (Jun 3, 2002)

ibericb said:


> So let me add, from the UCI document _Clarification Guide of the UCI Technical Regulation_, page 5:
> 
> 
> *Article 1.3.007*:
> ...


for one, you're missing real-world knowledge, although you do seem pretty quick with a google search return. One-offs are done routinely - the entire British road team did it for the 2012 Olympics with UK Sports Institute Frames. They were theoretically made available to the public on a website for about a week at an astronomical cost. This is standard practice for UCI track events as well.


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## Pirx (Aug 9, 2009)

Jackhammer said:


> So you acknowledge that Lyapunov exponents exist in the bicycle/rider system?
> 
> Before you mocked me and said they did not.


Sorry if you felt mocked. Other than that, the answer to your question would lead me too far afield to be appropriate for this forum. As of now, I'm still not sure if you have even a vague idea what a Lyapunov exponent is (please, no more links...). Not saying you don't, just that I can't tell.

In brief, sure, Lyapunov exponents exist, and trivially so; that's like saying lengths exist, or stiffness exists. The question is what is their relevance for the problem at hand? You tell us.


----------



## thumper8888 (Apr 7, 2009)

Pirx said:


> Hmm, you would think so, now, wouldn't you? So, how do you explain the fact that no publication exists, anywhere, wherein it would be explained in "painful, chart-and-wind-tunnel detail", how the S-Works Rigidity is 0.127 seconds faster over a 400k time trial than the competing hyper-flexy Giant Noodility? Why, might that be because perhaps no such results exist? Noooo, that can't be, or can it?
> 
> P.S.: I will refrain from even going into the utter ludicrousness of the idea that a couple of pieces of this-or-that carbon here or there, oriented this way or that way, would make one wit of a difference.


I'm about 30 feet from a 100-meter by 100cm roll of dry hi-mod uni... and even in a crude hand layup I can assure you that a few grams of it would indeed make a measurable difference in the stiffness of a specific joint. 20 grams, hell, probably even 10, at 45 degrees off axis in the downtube/head tube of an Sl4 would make the pros start whining again like they did about the sl3.

But. Getting back to the stiffness issue. Finally.
There is nothing in this thread that will settle the issue.
But if some trustworthy person were to say, fit a standard Reynolds 531 frame with a pedal or crank based power meter, then clamp it into a Wahoo, and run it steady for usable periods at say 200, 300, 600, 800 and 1000 watts, chart the difference between the input and output, then do the same with a bike known to be especially stiff torsionally, such as the S-works Tarmac, then we would know.


----------



## Pirx (Aug 9, 2009)

Yes, that suggestion has come up here before. One of the conclusions of that sub-thread was that, while certainly of interest, the result of such a test would not be conclusive. Notice that your test at best will only tell us something about the difference in power at the crank versus power at the hub. In particular, you really want a pedal-based powermeter for this; if it's crank-based, you're going to miss almost all of the relevant effects. 

Even with a pedal-based PM it will not tell us anything about the biomechanical side of things. There is good reason to assume that this latter part is at least as important, however.


----------



## Jackhammer (Sep 23, 2014)

Pirx said:


> Oh please, for the love of god... Do yourself a favor and refrain from talking about things you don't understand. *There are no positive Lyapunov exponents in the dynamical system we are discussing here.
> *
> The Einstein quote you gave does have some relevance, however: Yes, there are consequences of frame stiffness that can and do lead people to prefer such frames, even if there are no quantifiable performance benefits, and that's perfectly fine. Lots of people like red bikes better than blue ones, too. Or vice versa. That's different, however, since everyone knows that red bikes are faster.





Pirx said:


> Sorry if you felt mocked. Other than that, the answer to your question would lead me too far afield to be appropriate for this forum. As of now, I'm still not sure if you have even a vague idea what a Lyapunov exponent is (please, no more links...). Not saying you don't, just that I can't tell.
> 
> *In brief, sure, Lyapunov exponents exist, and trivially so*; that's like saying lengths exist, or stiffness exists. The question is what is their relevance for the problem at hand? You tell us.


You said "*t**here are no positive Lyapunov exponents in the dynamical system we are discussing here."


*Now you contradict yourself.

The links I provided showed they're not trivial.

You still haven't shown you know what "quantifiable" means. 

Define it and you'll show you have no idea as to the ramifications of the Einstein quote.

The ball is in your court.

You asserted stiffness contributing to performance is a "fairytale," not me.

PS, it's not that I "felt mocked" or care about it. You tried to mock me which I think is funny because your condescension has contributed to undermining your arguments. LOL


----------



## thumper8888 (Apr 7, 2009)

Pirx said:


> Yes, that suggestion has come up here before. One of the conclusions of that sub-thread was that, while certainly of interest, the result of such a test would not be conclusive. Notice that your test at best will only tell us something about the difference in power at the crank versus power at the hub. In particular, you really want a pedal-based powermeter for this; if it's crank-based, you're going to miss almost all of the relevant effects.
> 
> Even with a pedal-based PM it will not tell us anything about the biomechanical side of things. There is good reason to assume that this latter part is at least as important, however.


Yeah, I will buy all that. Makes sense. But it would get us a substantial way there.
Surely this is an easily doable test.


----------



## ibericb (Oct 28, 2014)

stevesbike said:


> for one, you're missing real-world knowledge, although you do seem pretty quick with a google search return. One-offs are done routinely - the entire British road team did it for the 2012 Olympics with UK Sports Institute Frames. They were theoretically made available to the public on a website for about a week at an astronomical cost. This is standard practice for UCI track events as well.


Thanks for sharing your wisdom, steve, I have no doubt that in the world of track bikes and Olympic teams there are some different choices made than those used in the pro peloton for road racing (which was the issue and point of contention), and those differences result in some apparent one-offs. In spite of that, aren't the frames in fact on the UCI approved list at the time they are used, and still would be available to the public within 9 months of their use, even if for a limited time? Is that not the case?

Back to the point here, can you enlighten us with your real-world knowledge -- who in the pro peloton rides a unique on-off or unique custom frame, not generally available to the buying public from the named manufacturer?


----------



## Pirx (Aug 9, 2009)

Jackhammer said:


> You said "*t**here are no positive Lyapunov exponents in the dynamical system we are discussing here."
> 
> 
> *Now you contradict yourself.


Ah, I see, reading comprehension issues. Lyapunov exponents are defined for any dynamical system. Not all dynamical system have _positive_ Lyapunov exponents. Those latter ones, in quasi-periodic systems, have special significance. In the hope that you have at least a vague idea of what it is you are talking about, I shouldn't have to say more. Right?



Jackhammer said:


> The links I provided showed they're not trivial.


Did you even read what I wrote? I said the _existence_ of Lyapunov exponents is trivial. I even gave you some analogies that illustrate in exactly what way this is trivial. Let me know if you need more help with this.



Jackhammer said:


> You still haven't shown you know what "quantifiable" means.


Seriously?



Jackhammer said:


> Define it and you'll show you have no idea as to the ramifications of the Einstein quote.


Seriously?



Jackhammer said:


> The ball is in your court.


What ball? I'm not playing ball with you until you have shown you're qualified. So far all I see is some crude baiting attempts. Oh yes, that's right, I have already told you that I'm not biting. So, put up some substance, and we'll talk. Right now you're trolling. Perhaps you can do better, but I don't know. My null hypothesis is that you have nothing. End of story.



Jackhammer said:


> You tried to mock me which I think is funny because your condescension has contributed to undermining your arguments. LOL


In your mind. That's fine with me. You're perfectly free to consider my arguments undermined. Some people may feel that arguments do, and need to, stand on their own, regardless of who proposes them, but perhaps you don't. Suit yourself.


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## Pirx (Aug 9, 2009)

thumper8888 said:


> Yeah, I will buy all that. Makes sense. But it would get us a substantial way there.
> Surely this is an easily doable test.


Yes, I agree. The one additional complication is accuracy: Standard off-the-shelf powermeters are typically only accurate to within 1.5% or so (SRAM offers a "science model", I believe, that gets that down to 0.5%, to the tune of $$$), so there's a good chance you will not see the effect you're looking for even if it's there. 1.5% of 300 Watts is 45 Watts, which is A LOT, and probably more than even people who believe in the benefits of frame stiffness would dream of.


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## stevesbike (Jun 3, 2002)

Pirx said:


> Yes, I agree. The one additional complication is accuracy: Standard off-the-shelf powermeters are typically only accurate to within 1.5% or so (SRAM offers a "science model", I believe, that gets that down to 0.5%, to the tune of $$$), so there's a good chance you will not see the effect you're looking for even if it's there. 1.5% of 300 Watts is 45 Watts, which is A LOT, and probably more than even people who believe in the benefits of frame stiffness would dream of.


This is definitely not the way you would do it. For one, a pedal-based powermeter would be affected by crank stiffness, which has been shown to result in up to 1.6% energy loss. It would be much better to use load cells and FEA.


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## ibericb (Oct 28, 2014)

stevesbike said:


> This is definitely not the way you would do it. For one, a pedal-based powermeter would be affected by crank stiffness, which has been shown to result in up to 1.6% energy loss. It would be much better to use load cells and FEA.


You still need to deal with the variations in angular velocity, which requires that you actually measure angular velocity dynamically. Certainly doable, but it makes the point - this isn't an simple power meter experiment.

FWIW, Rinard concluded that the differences, if there are any, were less than that which could be reliably measured. He suggested looking elsewhere for additional speed.


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## Pirx (Aug 9, 2009)

stevesbike said:


> It would be much better to use load cells and FEA.


I agree with this statement, somewhat. However, while the simple test suggested above could be performed by many hobbyists (lots of people now have crank- or pedal-based PMs, and quite a few have a Wahoo Kickr, too) with next to no effort, what you are suggesting, while superior, is also a far more challenging endeavor.

P.S.: I am intentionally not commenting on your estimate of "energy loss" due to crank flex.


----------



## davidka (Dec 12, 2001)

tvad said:


> I believe they are telling the truth. They specifically explain why you do not see them on the list.
> 
> Bottom line, it doesn't really matter to this discussion.


Where do they explain that? I cannot find an explanation on their site.


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## Jackhammer (Sep 23, 2014)

duplicate


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## Jackhammer (Sep 23, 2014)

Pirx said:


> Seriously?
> 
> 
> 
> Seriously?


Seriously, regarding quantifiable and Einstein's quote. Amazingly obtuse! Steam on!

Before you can address anything here, it's important to acknowledge that not everything that counts can be counted.



Do you think all the variables which cause muscular fatigue are quantifiable?

Frame stiffness is probably important for the same reasons that power cranks are probably an ineffective training device.


----------



## Jackhammer (Sep 23, 2014)

*I agree with your GENERAL*



Pirx said:


> This is somewhat of an old topic, and I think by now many of us understand that the still ongoing obsession with frame stiffness, in the form of "lateral stiffness", "stiff bottom brackets", etc., etc., is nothing but marketing BS. Yet, just about _every single article_ you see that presents a "review" of some new bicycle, and certainly _every single manufacturer blurb_ about the newest bike from manufacturer X still continues perpetuating this idiocy.
> 
> On the other hand, from the physics of bicycles it is entirely clear that frame flex, at the kind of level any halfway realistic, existing road bike will show, has almost exactly zero effect on the efficiency of "power transfer" (whatever that may mean; we note in passing that nobody ever bothers to define this term, and there is certainly not a single test or experiment of any kind that would demonstrate the relevance of this quantity). I have therefore argued for a long time that, if there is any effect of frame stiffness on performance at all, it would have to be sought in the biomechanical efficiency of the rider-bicycle system. However, a priori there is no reason to assume that this system will perform either better or worse using a stiffer frame. As a consequence, it may well be that some riders do better on more flexible frames, and some others may prefer stiffer ones. Bottom line: Nobody knows, and all the rest is nothing but clueless babble.
> 
> ...


"I have therefore argued for a long time that, if there is any effect of frame stiffness on performance at all, it would have to be sought in the biomechanical efficiency of the rider-bicycle system."

Contentions, particularly the above but at this point in time , being that it's almost impossible to measure and even determine the tiny biomechanical differences which probably do matter, you're not saying much of anything. 

The above seems fairly obvious. 

"Completely and utterly irrelevant?"

For racers, pro or amateur? 

I'd wager that not one race result would have ever been reversed had a rider ridden a more laterally flexible frame, all else being equal. 

Eventually you will be walking that absolute contention back.


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## tvad (Aug 31, 2003)

davidka said:


> Where do they explain that? I cannot find an explanation on their site.


It's covered earlier in this thread.


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## Pirx (Aug 9, 2009)

Jackhammer said:


> The above seems fairly obvious.


Oh yes, I agree, it _should_ be obvious. Obviously, it isn't, see this thread. 



Jackhammer said:


> "Completely and utterly irrelevant?"


Sure, there's a minor amount of hyperbole there.



Jackhammer said:


> Eventually you will be walking that absolute contention back.


A little bit, yes, but not much, and not in substance. It seems we agree on that.


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## Lombard (May 8, 2014)

With a buzzword like "fairytale", I just feel I have to reply.

I am always amused at how some post these infinitesimal numbers to try and prove that one bike is faster than another. Even if it's true, it will be such a small difference, none of us will ever notice a difference in speed.

Numbers and endless engineering mumbo jumbo aside, a stiffer frame and BB is definitely more of a pleasure to ride. Less lateral frame flex makes for more confident handling of the bike. Less BB flex makes for a much nicer feel accelerating from a stop.

None of these differences will translate to better Strava times that you can wow your bike buddies with. Then again, indirectly, they just may. Why? Because when you have a bike that is a greater pleasure to ride, you will ride it more and therefore become a stronger rider.


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## thumper8888 (Apr 7, 2009)

stevesbike said:


> This is definitely not the way you would do it. For one, a pedal-based powermeter would be affected by crank stiffness, which has been shown to result in up to 1.6% energy loss. It would be much better to use load cells and FEA.



Use the same crank. Use the same pedal meter. use the same wahoo. Use different frames.
At this rate of excuse making for NOT doing a test, there apparently is never going to be a test perfect enough to actually attempt.
The point is to try it and see what happens. And the quoted 1.6 percent error rate is meaningless for this purpose, if you use the same meters and make enough runs the truth will out. It wouldn't take many to see whatever pattern there is.....
And the error rate on mine is closer to 1 percent, if that much.
And BTW: 1.5 percent of 300 watts is of course NOT 45 watts. it's 4.5 watts.


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## Pirx (Aug 9, 2009)

thumper8888 said:


> And BTW: 1.5 percent of 300 watts is of course NOT 45 watts. it's 4.5 watts.


What can I say? When you're right, you're right... :blush2:


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## davidka (Dec 12, 2001)

Lombard said:


> .
> 
> Numbers and endless engineering mumbo jumbo aside, a stiffer frame and BB is definitely more of a pleasure to ride.


If it were that simple, aluminum bikes would sell a lot better.

A bike's ride quality and character comes from flex, not stiffness. Bomber stiff bikes are actually very easy to make.


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## Pirx (Aug 9, 2009)

Which reminds me: An interesting remark on the side is this: 
People should understand that the famed superior "vertical compliance" of carbon frames, or any increase in comfort via insulation from road roughness that a frame may afford you, would have to be to a large part attributed to _damping_ of vertical oscillations. It is important to note that any such damping will be associated with _energy losses_ and thus _potentially_ decreased "performance" of the bicycle. That's a new can of worms we could open up just in case people are getting bored with the lateral flex stuff.


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## Lombard (May 8, 2014)

davidka said:


> If it were that simple, aluminum bikes would sell a lot better.
> 
> A bike's ride quality and character comes from flex, not stiffness. Bomber stiff bikes are actually very easy to make.




OK, I should have elaborated and said "a* laterally* stiffer frame". Of course many aluminum bikes are quite stiff, but also quite harsh feeling. That is one great advantage to the latest carbon frames that can be shaped so they are stiff laterally where you want and not vertically stiff in order to be more compliant.

Of course, a bigger advantage in vertical compliance can be obtained with wider tires capable of less pressure.


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## Jackhammer (Sep 23, 2014)

davidka said:


> If it were that simple, aluminum bikes would sell a lot better.
> 
> A bike's ride quality and character comes from flex, not stiffness. Bomber stiff bikes are actually very easy to make.


Good grief!

*"Stiffness* is the rigidity of an object — the extent to which it resists deformation in response to an applied force. The complementary concept is flexibility or pliability: the more flexible an object is, the less stiff it is."



Lombard said:


> OK, I should have elaborated and said "a* laterally* stiffer frame". Of course many aluminum bikes are quite stiff, but also quite harsh feeling. That is one great advantage to the latest carbon frames that can be shaped so they are stiff laterally where you want and not vertically stiff in order to be more compliant.
> 
> Of course, a bigger advantage in vertical compliance can be obtained with wider tires capable of less pressure.


Don't worry about it. Everyone except the pedantically challenged knows what you were getting at.

To conclude, Pirx is probably about 99.5% correct, or more, that stiffness is essentially a fairy tale or bs, wrt to just about every decent bicycle of at least the last 30 years...


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## aclinjury (Sep 12, 2011)

Pirx said:


> Which reminds me: An interesting remark on the side is this:
> People should understand that the famed superior "*vertical compliance*" of carbon frames, or any increase in comfort via insulation from road roughness that a frame may afford you, would have to be to a large part attributed to _damping_ of vertical oscillations. It is important to note that any such damping will be associated with _energy losses_ and thus _potentially_ decreased "performance" of the bicycle. That's a new can of worms we could open up just in case people are getting bored with the lateral flex stuff.


"vertical compliance" - the act of bouncing off the saddle at regular intervals such that a fart can be released without resorting to using a out-of-saddle stand technique


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## Pirx (Aug 9, 2009)

aclinjury said:


> "vertical compliance" - the act of bouncing off the saddle at regular intervals such that a fart can be released without resorting to using a out-of-saddle stand technique


Sure, if you want to go all technical on us now. :thumbsup:


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## stevesbike (Jun 3, 2002)

thumper8888 said:


> Use the same crank. Use the same pedal meter. use the same wahoo. Use different frames.
> At this rate of excuse making for NOT doing a test, there apparently is never going to be a test perfect enough to actually attempt.
> The point is to try it and see what happens. And the quoted 1.6 percent error rate is meaningless for this purpose, if you use the same meters and make enough runs the truth will out. It wouldn't take many to see whatever pattern there is.....
> And the error rate on mine is closer to 1 percent, if that much.
> And BTW: 1.5 percent of 300 watts is of course NOT 45 watts. it's 4.5 watts.


actually, what I described has already been instrumented and tested, including 3-axis dynamometric pedals for dynamic testing (including standing sprinting rather than the static load tests criticized here) and strain gauges situated throughout the frame (positions optimized via FEA modeling). This was done in the context of BMX frame design, now an Olympic event, where efficiency is hugely important since races results are often separated by .01 seconds. 

FWIW, these tests report stresses of 70 MPa - considering that the flexible frames PIRX appears to champion have yield strengths of 250 MPa, simple safety coefficients and fatigue considerations (especially for aluminum alloys) seems enough of a counter-argument against the highly flexible frames PIRX (via his endorsement of BQ) suggests are superior to very stiff ones. My own n=1 anecdote is the Vitus I raced on circa 1988 - it was fine for about 6 months until it essentially disassembled before my eyes. I'm guessing PIRX doesn't generate much power, so has never had this be an issue - hence his endorsement of BQ in his 1st post of the thread.


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## Pirx (Aug 9, 2009)

stevesbike said:


> [...]considering that the flexible frames PIRX appears to champion have yield strengths of 250 MPa, simple safety coefficients and fatigue considerations (especially for aluminum alloys) seems enough of a counter-argument against the highly flexible frames PIRX (via his endorsement of BQ) suggests are superior to very stiff ones [...] I'm guessing PIRX doesn't generate much power, [...]


Pirx will simply note that it should be clear to anyone who is (a) in the full possession of his or her mental faculties, and (b) has read my posts in this thread, that the above characterizations of my position are complete nonsense. Specifically, I do _not_ "champion flexible frames", I have never "endorsed" BQ, and I have never suggested something as silly as highly flexible frames being superior to very stiff ones.

And of course, I will not dignify that lame little _ad hominem_ in Steve's last sentence with an answer. I will say that Steve might want to think about how compatible infantile nonsense of that sort is with the persona he is trying to project. We can all draw our own conclusions.


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## stevesbike (Jun 3, 2002)

Pirx said:


> Pirx will simply note that it should be clear to anyone who is (a) in the full possession of his or her mental faculties, and (b) has read my posts in this thread, that the above characterizations of my position are complete nonsense. Specifically, I do _not_ "champion flexible frames", I have never "endorsed" BQ, and I have never suggested something as silly as highly flexible frames being superior to very stiff ones.
> 
> And of course, I will not dignify that lame little _ad hominem_ in Steve's last sentence with an answer. I will say that Steve might want to think about how compatible infantile nonsense of that sort is with the persona he is trying to project. We can all draw our own conclusions.


You just continue to make stuff up. Let me remind you of what you in fact said in the first post:

PIRX: The reason I am repeating the above well-known truths is that I just happened to stumble over an older post in the Bicycle Quarterly and Compass Bicycles blog, which in fact quotes a few pieces of evidence confirming what I've been saying for years. Here is a pertinent quote:

“Many riders and builders extol the virtues of a “lively” frame made from flexible tubing. When we tested different frame tubing in a double-blind test (Bicycle Quarterly Vol. 6, No. 4), we found that two of three riders preferred the most flexible frame both for constant efforts and for all-out sprints. (The third rider could not tell the – very small – differences between the frames in our test.)”

BQ's study is the "evidence" that confirms your view - that's endorsing BQ's study no matter how you might want to try to back away from that one. The quote you said was the "pertinent" one champions "the most flexible" frame as the 2/3 preferred frame - all 3 were extremely flexible frames by today's carbon standards. The BQ study continues to offer their theory of "planing" for the preference, a study that is utter nonsense. Once I pointed this out, you tried to disavow yourself of the BQ link, but, again, it's what you began the thread with. Sorry, but if you cite a study as the evidence confirming your view, that's an endorsement. As for the ad hominem, they are essentially the only thing you've offered throughout this thread - insulting just about everyone without a single substantive comment. Of course, that fits your pattern - you want the thread to be about you, not the issue of frame stiffness.


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## velodog (Sep 26, 2007)

Pirx said:


> Which reminds me: An interesting remark on the side is this:
> People should understand that the famed superior "vertical compliance" of carbon frames, or any increase in comfort via insulation from road roughness that a frame may afford you, would have to be to a large part attributed to _damping_ of vertical oscillations. It is important to note that any such damping will be associated with _energy losses_ and thus _potentially_ decreased "performance" of the bicycle. That's a new can of worms we could open up just in case people are getting bored with the lateral flex stuff.


Troublemaker. :lol:


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## Pirx (Aug 9, 2009)

stevesbike said:


> [stomping his little foot]


Still hurting so much? I'm sorry, Steve.


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## stevesbike (Jun 3, 2002)

Pirx said:


> Still hurting so much? I'm sorry, Steve.


nope, I"m just fine, thanks for asking, though. Noticed you continue to refuse to provide any substantive comments or replies especially when your denials are flatly contradicted by your previous posts. It's easier, I guess, than admitting you in fact sourced the most nonsensical study in 'cycling science' as confirmation of your view. Fortunately, more disinterested readers of this forum ought to have no difficulties seeing the blatant contradictions of your statements in the above post.


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## Pirx (Aug 9, 2009)

You know, Steve, I was serious when I said I was sorry. I know you don't believe me, but I really am sorry to see you reduced to this state. You need to try and get over this. Get some help.


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## tvad (Aug 31, 2003)

Reduced to accusations of psychological disorder.

Does it get any better than this folks!


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## goodboyr (Apr 19, 2006)

I guess you don't wander over to the wattage Google group too often. This is child's play compared to that. They just shut down the group for the weekend again to give the kids a time out. Priceless.


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## stevesbike (Jun 3, 2002)

Pirx said:


> You know, Steve, I was serious when I said I was sorry. I know you don't believe me, but I really am sorry to see you reduced to this state. You need to try and get over this. Get some help.


deflection will get you nowhere (pun intended). You also said this in the first post:

"However, a priori there is no reason to assume that this system will perform either better or worse using a stiffer frame. As a consequence, it may well be that some riders do better on more flexible frames, and some others may prefer stiffer ones." 

Leaving aside the confused and ambiguous language - performance, preference, and whatever "do better on more flexible frames" could possibly mean, this is a paraphrase of Jan Heine's planing theory. To remind other readers what that amounts to, here's the evidence you referred to:









According to BQ, the same rider produced 15% more power on the more flexible bike 2 than bike 1. 15% - greater than any PED you could take, an astonishing amount that would let a backwards country to dominate Olympic events if only they rode flexy frames. Heine has all sorts of hand-waving arguments re how a flexible frame does this, but the main point is that if you don't believe planing then the best a flexible frame could do in principle would be to be as efficient as a stiffer one. But that's boring. Hardly worthy of such a long thread and something you denied about 100 posts ago...


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## Pirx (Aug 9, 2009)

Yes, Steve. Heine is a bad person. Bad, _bad_ Heine. 

Feeling better now? No, not yet? 
Alright: Heine's "planing theory" is a terrible theory. Complete nonsense. Utter rubbish.

How about now? Did that help? Good. Don't mention it, I'll send you a bill.

P.S.: I'll tell you a secret: I actually do mean what I said about Heine's "theory". Well, it's not much of a secret really, since I have said that before, if you care to check. Anyhow, I thought perhaps it'll make you feel better.


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## OldChipper (May 15, 2011)

So look, here's my deal, "planing" or whatever, if someone can't explain, in simple terms that everyone can understand, how lateral flex converts to either forward or rotational motion, then they don't really understand it either and I'm not inclined to believe them since they're just appealing to authority. Insults and claims of superior knowledge don't feed the bulldog. 

Steven Hawking can explain blackholes so the average Joe can understand them FFS - this is just bikes 'n ****. :idea:


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## Pirx (Aug 9, 2009)

An explanation in simple terms has been given in this thread, several times. It has also been explained that, at a higher level it is clear that such effects _must_ exist due to energy conservation arguments for the case of a "mechanical rider".

And, no, Stephen Hawking does not and cannot _explain_ black holes in a way the "average Joe" can understand. He and I can explain to you _roughly_ what these are in terms of some vague analogies, plus some fun little tidbits here and there, but you cannot _understand_ these objects without a solid background in modern physics. 

[RANT]
I will note that I find this popular idea (that any "average Joe" could fully understand any result of modern science if only someone would explain it right) indeed highly insulting. Getting to the point where someone can understand the mathematics and the physics of General Relativity and Quantum Mechanics pertinent to black holes takes both _years_ of hard work, and an amount of intellectual horsepower that only a relatively small number of people are gifted with. The idea that the "average Joe" could understand this material within the limits of his attention span is completely ludicrous. So what are all those fools studying at universities _for years_ in order to be able to understand the core theories of modern physics wasting their time with? After all, all they need to do is read Hawking's "Brief History of Time", and it's all there, right? Sheesh...

So, what the "average Joe" can do is _accept_ certain results from modern physics that say those objects exist, and that they have been observed through certain effects that are predicted by such theories. But, no, the "average Joe" cannot even begin to understand black holes as the quasi-singularities of space-time structure that they are. The idea that he could comes from a deep-seated streak of anti-intellectualism that is part of the fabric of American culture. All that scientists can do is explain what some of the results of their theories mean, but it is impossible for the layperson to understand how those results come about. To go completely off-topic now, I will add that this is also the core problem of that insufferable Global Warming debate: Fools that have no standing in such a debate feeling they can weigh in on a subject matter they have absolutely no grasp of. The main difference is, almost nobody cares much about black holes one way or another, but a lot of people have some thoroughly misguided opinions about the weather...
[/RANT]

To get back closer to our topic, if you pay attention to those "explanations" of black holes you are referring to, you will find that they are along the lines of "We have an extremely well-validated theory according to which such and such is the case"; this is the same level of explanation that says "according to both theoretical models and statistical evidence from measurement data we know that significant increases in the global temperature are occurring". And it is the same level of explanation as saying "we know from theoretical mechanics that lateral frame flex is converted back to propulsive forces".


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## Pirx (Aug 9, 2009)

stevesbike said:


> actually, what I described has already been instrumented and tested, including 3-axis dynamometric pedals for dynamic testing (including standing sprinting rather than the static load tests criticized here) and strain gauges situated throughout the frame (positions optimized via FEA modeling).


Out of idle curiosity: You wouldn't be able to provide a reference, or would you? While you're at it, why don't you provide a reference for this one, too:



stevesbike said:


> a pedal-based powermeter would be affected by crank stiffness, which has been shown to result in up to 1.6% energy loss.





stevesbike said:


> FWIW, these tests report stresses of 70 MPa - considering that the flexible frames PIRX appears to champion have yield strengths of 250 MPa,


More curiosity: If you ever get around to it, please do let us know what you think the relevance of this fascinating little tidbit of information might be. Feel free to look up the yield strengths of frame materials used for bicycles before you do so. By all means, let us know what you find. Thank you.


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## aclinjury (Sep 12, 2011)

I know this is an old thread.

But here's an updated podcast with Jan Heine and Damon Rinard discussion frame stiffness.

https://cyclingtips.com/2017/06/cyclingtips-podcast-does-frame-stiffness-matter/

Basically, it boils down to stiffness does not necessarily mean faster.

Credit to velodog for posting the podcast here:
http://forums.roadbikereview.com/bikes-frames-forks/frame-stiffness-360904.html#post5156601


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## Jay Strongbow (May 8, 2010)

aclinjury said:


> I know this is an old thread.
> 
> But here's an updated podcast with Jan Heine and Damon Rinard discussion frame stiffness.
> 
> ...


But in my experience it does mean slower. Well, if your rides are of any real distance or the road surface sucks.

I had a German carbon wonder bike that was tops in Tour magazines stiffness to weight test in the year it was made. Rode it about 40,000 miles and liked every bit of it.
I'd since gotten a ti bike that's stiff enough but not that stiff. Like that even more.
Pretty sure I'm a lot faster after 40 or so miles if the roads aren't great on the less stiff (thus smoother) ti bike. I have nothing to back it up and maybe I'm just stronger this year but taking care of the engine with a smoother ride does a lot more for speed than BB stiffness seems to be the case to me.


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## nhluhr (Sep 9, 2010)

Jay Strongbow said:


> But in my experience it does mean slower.


There is logically a difference between 'stiffness' in terms of rider fatigue and 'stiffness' in terms of mechanical efficiency. The old "lateral stiffness, vertical compliance" thing.


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## Jay Strongbow (May 8, 2010)

nhluhr said:


> There is logically a difference between 'stiffness' in terms of rider fatigue and 'stiffness' in terms of mechanical efficiency. The old "lateral stiffness, vertical compliance" thing.


I know. In theory sure but the reality with any bike I've every been on is you can't have your cake and eat it too. You need to give up some to get some with regard to the the old "lateral stiffness, vertical compliance" thing.
Maybe there's a frame out there that would be stiff and snappy under Andre Griepel and be nice an smooth under a weekend warrior riding a century on bad roads....but I tend to doubt best of both worlds is available and it's about compromise between the two.


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## bradkay (Nov 5, 2013)

Look at the Trek Domane. It is Fabian Cancellara's favorite bike.


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## aclinjury (Sep 12, 2011)

I think the podcast with Heines and Rinard sort of validates what Pirx had said.

Damon Rinard's (used to be with Cervelo and now with Cannondale) position about frame's stiffness has changed. He used to be a champion on frame stiffness, but now he is saying in this podcast to just completely ignore bottom bracket stiffness in your next bike purchase. Rinard is now agreeing more with Heines.

now I just want to mention this little tidbit mentioned by Stevesbike in his post#97:


> For the record, Cervelo did these sorts of tests with their strain gauge test bike and reported losses up to 4%


This measurement was most likely done when Rinard was still was Cervelo. Well, in the podcast, it seems that Rinard is saying that that "loss" in energy is due to noise and that there could have been no loss or a very very minimal loss such that one could completely ignore it.


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## aclinjury (Sep 12, 2011)

bradkay said:


> Look at the Trek Domane. It is Fabian Cancellara's favorite bike.


well it has to be since he was sponsored to ride it, but I agree the Domane is a smooth bike with wide rims and 25mm tubular. Butter.


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## aclinjury (Sep 12, 2011)

Jay Strongbow said:


> But in my experience it does mean slower. Well, if your rides are of any real distance or the road surface sucks.
> 
> I had a German carbon wonder bike that was tops in Tour magazines stiffness to weight test in the year it was made. Rode it about 40,000 miles and liked every bit of it.
> I'd since gotten a ti bike that's stiff enough but not that stiff. Like that even more.
> Pretty sure I'm a lot faster after 40 or so miles if the roads aren't great on the less stiff (thus smoother) ti bike. I have nothing to back it up and maybe I'm just stronger this year but taking care of the engine with a smoother ride does a lot more for speed than BB stiffness seems to be the case to me.


my personal experience is I have always put out the highest avg power and highest normalized power when I'm hammering on my carbon-ti (flexy) bike on the flat, when compared to my full carbon bike (which is definitely stiffer). My heart rate would stay the same yet amazingly my avg power would be like 20 watts more in a 5-10 minute hard effort. I do like the springy feeling of the bottom bracket of the carbon-ti bike.

on another note, I think by now, the mantra that carbon frame can be both "stiff laterally and compliant vertically" is pie-in-the-sky wish. No way to make a bike both stiff and compliant with carbon fiber even though in theory this should be possible (by adjusting carbon layups). Now, bike companies are relying on other tricks like put using an "elastomer" in the seattube or headtube, lol. So they've have given up on the "stiff and compliant" dream, just insert a piece of elastomer now.


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## bradkay (Nov 5, 2013)

aclinjury said:


> my personal experience is I have always put out the highest avg power and highest normalized power when I'm hammering on my carbon-ti (flexy) bike on the flat, when compared to my full carbon bike (which is definitely stiffer). My heart rate would stay the same yet amazingly my avg power would be like 20 watts more in a 5-10 minute hard effort. I do like the springy feeling of the bottom bracket of the carbon-ti bike.
> 
> on another note, I think by now, the mantra that carbon frame can be both "stiff laterally and compliant vertically" is pie-in-the-sky wish. No way to make a bike both stiff and compliant with carbon fiber even though in theory this should be possible (by adjusting carbon layups). Now, bike companies are relying on other tricks like put using an "elastomer" in the seattube or headtube, lol. So they've have given up on the "stiff and compliant" dream, just insert a piece of elastomer now.


How about a design that instead of "using an elastomer" just allows the seattube or the steertube to flex fore and aft while limiting it from flexing side to side?


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## Jackhammer (Sep 23, 2014)

Lombard said:


> With a buzzword like "fairytale", I just feel I have to reply.
> 
> I am always amused at how some post these infinitesimal numbers to try and prove that one bike is faster than another. Even if it's true, it will be such a small difference, none of us will ever notice a difference in speed.
> 
> ...


Hole shots?


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## nhluhr (Sep 9, 2010)

bradkay said:


> How about a design that instead of "using an elastomer" just allows the seattube or the steertube to flex fore and aft while limiting it from flexing side to side?


I'm not saying I agree with the whole picture but, the problem with an elastomer is it acts as a damper (to dull vibrations) which in other words absorbs kinetic energy and converts it to heat. The whole point Jan Heine has been making is that the metal bikes when they "plane" are storing the energy in purely elastic strain and returning it in a normalized way once the stress that initiated that strain (power stroke of the cadence) is gone. So an elastomer is really only going to help smooth the ride without that supposedly beneficial strain battery.


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## woodys737 (Dec 31, 2005)

aclinjury said:


> *my personal experience is I have always put out the highest avg power and highest normalized power when I'm hammering on my carbon-ti (flexy) bike on the flat, when compared to my full carbon bike (which is definitely stiffer). My heart rate would stay the same yet amazingly my avg power would be like 20 watts more in a 5-10 minute hard effort. I do like the springy feeling of the bottom bracket of the carbon-ti bike.*
> 
> on another note, I think by now, the mantra that carbon frame can be both "stiff laterally and compliant vertically" is pie-in-the-sky wish. No way to make a bike both stiff and compliant with carbon fiber even though in theory this should be possible (by adjusting carbon layups). Now, bike companies are relying on other tricks like put using an "elastomer" in the seattube or headtube, lol. So they've have given up on the "stiff and compliant" dream, just insert a piece of elastomer now.


This (your post and the greater context of the recently referenced Podcast which I listened to) is fascinating as I ditched an Aero Felt AR for the thinner tubed and more flexible F. I wrote a post about it somehwere here but, the gist was that in a straight line after a year of roll down tests, and all kinds of other power related testing, I could only come up with about 0.25mph faster on the AR. Some position. Same wheels/tires and group. Some power meter. And by same wheels/power meter I mean I swapped back and forth for the test.

However, when it came down to racing, I don't know man. I always ended up in a better position or was able to maneuver myself quicker (whatever) to be in the right spot with the F which is a large part of doing well. Could be total bullshit but, it was apparent enough that I sold the AR. 

Maybe they will come up with a thinner walled aero frame soon.


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## aclinjury (Sep 12, 2011)

bradkay said:


> How about a design that instead of "using an elastomer" just allows the seattube or the steertube to flex fore and aft while limiting it from flexing side to side?


though I don't own a Trek, but their "isospeed" system where they make the seatpost articulate (thus flexible) without resorting to an elastomer is a great idea, I was impressed when I tried it on the Madone 9. I ride a carbon-ti Serotta Ottrott, and when i sit on most pure carbon bikes I always think they're too stiff and harsh, but the Domane makes me think twice about Trek's "isospeed" system. Having said that, the Domane is still not quite on par with my Serotta Ottrott when it comes for comfort. Elastomer is so 1990, back in those days early mountain bikes had used them, lol


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## aclinjury (Sep 12, 2011)

woodys737 said:


> This (your post and the greater context of the recently referenced Podcast which I listened to) is fascinating as I ditched an Aero Felt AR for the thinner tubed and more flexible F. I wrote a post about it somehwere here but, the gist was that in a straight line after a year of roll down tests, and all kinds of other power related testing, I could only come up with about 0.25mph faster on the AR. Some position. Same wheels/tires and group. Some power meter. And by same wheels/power meter I mean I swapped back and forth for the test.
> 
> However, when it came down to racing, I don't know man. I always ended up in a better position or was able to maneuver myself quicker (whatever) to be in the right spot with the F which is a large part of doing well. Could be total bullshit but, it was apparent enough that I sold the AR.
> 
> Maybe they will come up with a thinner walled aero frame soon.


I'm a classic round tube and steel guy, never did embrace aero frame, maybe because i know aero frames are like chasing the latest tech, their lifecycle is short, you find them on fleabay shortly thereafter!


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## ruckus (Apr 1, 2014)

woodys737 said:


> This (your post and the greater context of the recently referenced Podcast which I listened to) is fascinating as I ditched an Aero Felt AR for the thinner tubed and more flexible F. I wrote a post about it somehwere here but, the gist was that in a straight line after a year of roll down tests, and all kinds of other power related testing, I could only come up with about 0.25mph faster on the AR. Some position. Same wheels/tires and group. Some power meter. And by same wheels/power meter I mean I swapped back and forth for the test.
> 
> However, when it came down to racing, I don't know man. I always ended up in a better position or was able to maneuver myself quicker (whatever) to be in the right spot with the F which is a large part of doing well. Could be total bullshit but, it was apparent enough that I sold the AR.
> 
> Maybe they will come up with a thinner walled aero frame soon.


Aero bikes seem relative to ability. From the tests I've seen done by GCN, Cyling Magazine, Bike Radar etc is that you don't see watt savings, improved efficiency until nearly 40 KMPH. Last data dump on Strava showed average man rides about 15mph, at those speeds, the difference between Aero and comfort light bike is nearly nil. The bike manufacturers state that too, see some marketing material that claim 50 watt savings @ 50 kmph or similar. If I was Sagan that would make a difference, but I can't ride 30 mph, not even close, i average 18? So based on that, I'll stick to the light weight standard bikes.


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## akropilot (May 22, 2007)

*Another empirical observation*

I ride 3 bikes
A hi-modulus 13.5lb NeilPryde BURA SL
A non hi-mod 16lb gen 1 Scott Addict
A 23lb 1986 Steel Colnago L'eroica bike

The interesting contrast is the Addict compared to the BURA. The BURA is much stiffer than the Addict in the front end and bottom bracket, it accelerates more 'abruptly' although I won't say it's faster. The BURA is so stiff that it's harder to ride smoothly, and I'm convinced harder to apply consistent power inputs. One might suggest reducing the amount of carbon layup, but this would only result in a fragile frame.

The BURA is great for crits, and maybe hillclimbs, but I'll be swapping it out for something new next year for general riding.

Ironically, the 8-pound-heavier Colnago is amazingly smooth and enjoyable to ride, and is just as fast as the carbon machines on flat ground.

Summary observation: Stiffness beyond a point is counterproductive to smooth power transfer (and general handling of course). This is why the top-rated frames such as Specialized SL5 have worked very hard on that blend.


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