# Crank stiffness, Does it make that much difference?



## farva (Jun 24, 2005)

I've been reading alot of threads recently about crank X being a little stiffer than crank Y & was just wondering how much difference this really makes at the end of the day? It seems that if you are sitting & pedal effeciently, crank flex should be a non issue. If you are standing, most of the downward force is applied to the cranks stiffest plane & very little energy would be lost to "side flex". Does this sound reasonable or am I way off? Just curious as I've never been able to notice any difference in flex on the handfull of cranksets I have used


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## Kerry Irons (Feb 25, 2002)

*You've got it*

The measured differences in crank stiffness are so small as to indistinguishable to a human. You are really looking at the total stiffness of the pedals, cranks, shoes, chainrings, BB, and frame. I used to ride with a guy who was sure that my frame was really flexy, from what he had read. He said "I bet you get chain rub all the time." I hadn't either noticed or thought about it, so I said "Let's see," and stood up and accelerated. Gee no chain rub. WHAT TO DO?! Maybe I had my front derailleur adjusted so that I didn't get chain rub. Maybe I'm weaker than a 7 year old. Maybe my frame was more flexible than some others, but only in lab measurements and not in a meaningful way in actual use. Of course, I've since read that my frame is "really stiff" and beats you up. Now I'm really confused  At any rate, it's important to separate something you can measure from something that has meaning. For the vast majority of riders, crank stiffness should be a relatively minor concern when choosing between brands and models.


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## farva (Jun 24, 2005)

Thanks. Yeah, I'm thinking the actual riding difference in flex between good quality cranksets is negligable.


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## Nessism (Feb 6, 2004)

farva said:


> Thanks. Yeah, I'm thinking the actual riding difference in flex between good quality cranksets is negligable.



I know for a FACT that the new style Shimano cranks, with the large 24mm integrated bottom bracket spindle, has less chain rub on the front derailleur than both an Octalink version crank and square taper. I don't think I'm faster with the new style cranks but the reduction in chain rub is worth the upgrade cost in my opinion.


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## Vinokourov (Oct 6, 2005)

*Difference is there but...*

... it might not justify the extra costs depending on the type of riding you do.

Personal experience with different equipement tells me that manufacturers are not lying when they claim their products are stronger or shift better or watever but you can only feel the slight improvements when you push you bike limits.. A stiffer crank is noticable by a strong/heavy rider or a monster sprinter but if are a tourer/non racer its better to save the money on other things.


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## pwagle (Jul 4, 2005)

Also depends on your physique/strength. At 6'4, 195-200 and a grinder at times, I did notice the difference moving up from an older FSA to the new 7800 DA crank. The new BB system and less chain rub is an added bonus.


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## farva (Jun 24, 2005)

OK. Thanks for all the replies. Could be I just never noticed any flex since I weigh 145 lbs. I am currently riding FSA cranks with the Shimano octalink interface. I have never noticed or felt the chain rub on the front derailluer. It certainly makes sense that it would be more noticeable if you are a big guy.


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## Spinfinity (Feb 3, 2004)

*Chain rub?*

My weight varies from 170 to 200 lbs. I'm not much of a spinner and comfortably climb all but a few of the hills in Central Connecticut standing and slowly hammering a 44x15 on my fixie. On my geared bikes I ride much the same way and have never been able to produce chain rub that defied adjusting away. 

I'm sure there are bigger and stronger riders than me, but even if the cranks flexed I doubt it would register much at the outer edges of the chain rings. I could visualize bottom bracket flex showing up there if it actually happens, or if the contact with the bottom bracket spindle were loose, but don't picture quite how a flexing crank arm would move the chain ring side to side.


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## elviento (Mar 24, 2002)

On a recent ride, I was trying to power through a crossing before the light turned red, and the frame/BB/crank flexed so much the chain completely came off on the inside. The pedals lost resistence and I had to swerve to recover. That's how much flex you can get. And the whole set up consisted of some of the most respected brands in the industry. When I took the bike apart to sell the frame, I confirmed installation was not the cause. Admittedly the flex seems mostly from the frame in this case, but I would go for every opportunity to make the ride stiff. 

I remember when threadless first came out, people bashed it for adding little benefit and the same happened to oversized handlebar. Today I wouldn't even ride a threaded setup with non-OS bars even if you give me the stuff for free. 




rusa1586 said:


> My weight varies from 170 to 200 lbs. I'm not much of a spinner and comfortably climb all but a few of the hills in Central Connecticut standing and slowly hammering a 44x15 on my fixie. On my geared bikes I ride much the same way and have never been able to produce chain rub that defied adjusting away.
> 
> I'm sure there are bigger and stronger riders than me, but even if the cranks flexed I doubt it would register much at the outer edges of the chain rings. I could visualize bottom bracket flex showing up there if it actually happens, or if the contact with the bottom bracket spindle were loose, but don't picture quite how a flexing crank arm would move the chain ring side to side.


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## divve (May 3, 2002)

You sold your Time VXRS already?


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## lemond2001 (Nov 22, 2001)

Here is some examples to yes the outboard bbb works. I have an old road Race Face cranks and square bottom bracket I road all the time. I switched to the newer octalink and dura ace cranks and notice a big improvement over the older setup I had. I still had chain rub and sometimes sprinting really hard had the chain fall off the crank. I then went to the a FSA Pro Elite cranks and Race Face ISIS bottom bracket. Did not notice any difference in stiffness but again chain rub and chain falling off during sprinting. 
I am now on  the new 10spd Dura Ace crank, BB and do not have any chain rub anymore, nor do I drop the chain during sprinting. Big difference. I can feel just how much stiffer the setup is while riding. Feels like all my power is going straight to the rear wheel.

square BB 17mm spin
Octa/ISIS 22mm spin (25 to 30% increase in stiffness FSA says over the square BB)
outboard 24mm spin (8 to 10% increase in stiffness over Octa/ISIS)

All this is on the same frame, wheels..

I have come to think that if you are up to around 170pds you could ride anything and not really notice any big changes. Over 170pds you can start to feel flexing in parts. I am 220pds and everything flexes. If I was a company I would use guys over 200pds to test my stuff for problems.

Anyways hope this helps.....


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## elviento (Mar 24, 2002)

The VXRS is staying. I love it. 



divve said:


> You sold your Time VXRS already?


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## altidude (Nov 14, 2002)

Many of the top sprinting pros in the world ride square taper bb, conventional Campy cranks and have no issues with flex. These guys are a lot stronger than most in here. That ought to give you a little perspective on the topic. Placebo effect is prevalent in the cycling world just like other recreational endeavors.


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## bikeboy389 (May 4, 2004)

I've found that frame flex had a lot more to do with chain rub than my cranks/BB. I've never met a bike I couldn't cause chain rub on, until my new one. That one's steel, with a square taper Phil Wood BB and Campy Chorus cranks--the same ones that were on my other steel frame, where I COULD cause chain rub. Based on this, I have to blame the frame, not the cranks/BB.


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## Nessism (Feb 6, 2004)

altidude said:


> Many of the top sprinting pros in the world ride square taper bb, conventional Campy cranks and have no issues with flex. These guys are a lot stronger than most in here. That ought to give you a little perspective on the topic. Placebo effect is prevalent in the cycling world just like other recreational endeavors.


Square taper cranks are more than stiff enough to transfer energy to the rear whee effectively; racers know this. Stiffness in cranks (or frames) does NOT make the bike faster. This is not to say that they are stiffer than Octalink/ISIS or Integrated spindle cranks though. 

I have two homemade frames that are almost identical except for the frame tubing; one is noticeably stiffer than the other. The more flexible frame has the stiffer 7800 crank and has NO chain rub when sprinting. The stiffer frame has a 7700 crank and gets a little chain rub if the front derailleur is not centered when sprinting. To me the difference is noticeable since I HATE to hear chain rub.

Doubt if you like but I have back to back experience with trying these different cranks and feel the difference is clear.

Ed


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## winstonc (Nov 18, 2002)

lemond2001 said:


> square BB 17mm spin
> Octa/ISIS 22mm spin (25 to 30% increase in stiffness FSA says over the square BB)
> outboard 24mm spin (8 to 10% increase in stiffness over Octa/ISIS)


Flex in the spindle itself is not the only factor; there's also flex of the spindle relative to the frame. With bearings supporting the spindle further out (as they do on the external bearing systems), the tendency for the spindle to be moved off-axis should be reduced.


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## curlybike (Jan 23, 2002)

*Crank stiffness seems to dimish with age.*

Hmmmm


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## Dave Hickey (Jan 27, 2002)

farva said:


> I've been reading alot of threads recently about crank X being a little stiffer than crank Y & was just wondering how much difference this really makes at the end of the day? It seems that if you are sitting & pedal effeciently, crank flex should be a non issue. If you are standing, most of the downward force is applied to the cranks stiffest plane & very little energy would be lost to "side flex". Does this sound reasonable or am I way off? Just curious as I've never been able to notice any difference in flex on the handfull of cranksets I have used



With very few exceptions, I don't buy the crank flex argument. 

Chain ring flex, yes....Crank/BB flex, no.... 

If you think about it, a crank is a thick chunk of aluminum or carbon. A chain ring is a thin piece of aluminum...Cut some holes in the aluminum ring and it's even less stiff. The ring is going to flex before the crank.

The much hyped Velo News test that the Dura Ace crankset won says nothing about chain rings. The new Dura Ace chain ring is very solid compared to the older rings with cutouts.


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## Nessism (Feb 6, 2004)

Dave Hickey said:


> With very few exceptions, I don't buy the crank flex argument.
> 
> Chain ring flex, yes....Crank/BB flex, no....
> 
> ...



No doubt the solid chain ring on the DA crank is a stiffer piece but this is NOT the main reason for reduced front derailleur chain rub, it's due to the large bottom bracket spindle and the outboard bearing placement. I say this from experience since I also have a 6600 crank and a FSA Mega Exo crank, both of which have conventional chain rings and both of these crank/bottom bracket assemblies exhibit reduced chain rub compared to a 7700/Octalink crank.


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## ColdRider (Mar 17, 2005)

This is an oldie, but goodie article. Their test evaluates *crank* stiffness only, not BB/Crankset stiffness. Their bottom line : if your legs can feel a 0.01 inch deflection difference then yes some cranks are "stiffer" then others.

I am a flyweight so words like "flex" and "stiffness" aren't part of my daily problems. I am more concerned about not getting beat up during long rides and crosswinds...

http://www.bikesportmichigan.com/reviews/crank.shtml


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## divve (May 3, 2002)

Define flyweight?


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## ColdRider (Mar 17, 2005)

105 lbs - 110 on a good day


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## divve (May 3, 2002)

Ok. I guess that pretty much qualifies.


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## ColdRider (Mar 17, 2005)

Thanks  I lusted after deep-section wheels earlier this summer (mostly for bling factor I'll admit). But after ridding all summer around Montreal (along the St-Lawrence River) and getting blown around from time to time with normal rims, I put that lusting to rest now. I think I can count on one hand the number of days when there was calm winds. No Shamals for me  

CR


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## foz (Sep 30, 2004)

I too think the whole 'crank flex' thing is not really anything to worry about. There are so many factors that can combine in many ways to cause or eliminate chain rub. The material and construction of the frame, bb, crank and rings all effect chain rub. So can the way they are put together - a slightly loose chainring bolt may be tight enough to hold the rings on the crank with no problems, but have a tiny amount of play that could cause the ring to deflect more than normal at that point. Lower quality bb/crank interfaces may have a similar (tiny) amount of play that can cause a deflection at the chainring teeth, even if the cranks are the stiffest available. 
Having said that, I am looking for a new crank and BB, and the integrated system seems like a good idea. I run campag, and really like the record carbon crank (for the looks), but like many others think it´s overpriced, so I´m looking at FSA. The K-force megaexo is quoted at 785g (BB included) on their website, but a superlight crank combined with their platinum pro ti megaquad BB comes to a total of 690g. Even the carbon pro team or SLK chainsets with the non-ti BB weigh less than the K-force megaexo. If there is no noticeable difference in crank/BB stiffness, why the big deal over the megaexo design if for more or less the same money you can get something just as good but 100g lighter? Basically i´m trying to decide whether i should jump on the megaexo bandwagon, or stick with a more traditional separate crank/BB and save those 100g. Any ideas?

Foz


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## divve (May 3, 2002)

If you really want to save weight go for the THM Clavicula - depending on ring sizes 535- 550g including BB. Comparable stiffness to DA10.


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## foz (Sep 30, 2004)

i´m no weightweenie, and the clavicula is probably way too expensive for me anyway. plus i don´t get the idea of naming a crank "collarbone" in spanish!!! maybe it´s so fragile it´s the bit you´re most likely to break on the bike in a fall!
I was just wondering if the supposed benefits of the megaexo system (stiffness, bearing life) outweigh the 100g weight penalty over the more traditional system. If a traditional crank and separate crank arm is more than stiff enough and no-one can tell if one setup is different to another anyway, then why bother with the megaexo?
That said, I will probably go with a K-force megaexo (changing out the rings for more traditional ones - i don´t like the "filled-in" look), if i can´t find a record carbon at the same price.

foz


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## winstonc (Nov 18, 2002)

foz said:


> If there is no noticeable difference in crank/BB stiffness, why the big deal over the megaexo design if for more or less the same money you can get something just as good but 100g lighter? Basically i´m trying to decide whether i should jump on the megaexo bandwagon, or stick with a more traditional separate crank/BB and save those 100g. Any ideas?



You could also run it the other way... if there's no noticeable diferrence in weight, why not go for the stiffer crank? Differences in weight have been tested on a scale, but probably won't be noticeable on the bike. Differences in stiffness have been tested in a lab setting, but may not be noticeable when you're on the bike -- although some people claim they can tell. I guess one thing this leaves out is that, while we do know how weight affects performance, we don't know how much crank stiffness affects performance.

Anyway, the biggest plus of the external-bearing design in my opinion is that they're way easier to install and remove. Once you figure out how to do it, it takes two minutes to take out the crank and BB -- one minute if you're really fast. Also, if you feel comfortable pressing bearings, you can replace the bearings with inexpensive ($7-20 each) standard ones instead of paying exorbitant prices for a good BB with custom bearings.


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## winstonc (Nov 18, 2002)

ColdRider said:


> This is an oldie, but goodie article. Their test evaluates *crank* stiffness only, not BB/Crankset stiffness. Their bottom line : if your legs can feel a 0.01 inch deflection difference then yes some cranks are "stiffer" then others.
> 
> I am a flyweight so words like "flex" and "stiffness" aren't part of my daily problems. I am more concerned about not getting beat up during long rides and crosswinds...
> 
> http://www.bikesportmichigan.com/reviews/crank.shtml



I'm not a big fan of the experiment they did because they measured the vertical flex of the drive-side crankarm. It seems to me that most of the flex will be torsional flex on the crank, since the pedal spindle acs as a lever arm. The photo below from cyclingnews shows what I'm talking about.

In a real-world situation, there are many other forces acting on the crank/BB system besides the in-plane one they measured. There's torsional flex in the spindle (relevant only for the non-drive side), bending moment on the spindle, and torsional flex in the crankarms. There's also chainring flex, but my _guess_ is that this is quite small since the force is in the plane of the ring, and there's a lot of material to support it.

I'm surprised that no one has mentioned the French magazine (Velo?) test from a couple years back. This test was done on a Cannondale frame, with a chain running from a chainring to a cog in the back. Doing a little math from their numbers, one can see that at the left pedal, the deflection under 200lbs of force was about 2cm for a typical crank, and the difference between the stiffest and the flexiest was something like 20% (~4mm under 200lbs) -- and remember, this is while taking frame flex into account. There was a long thread on this way back...

How much does flex matter for performance? I don't think anyone really knows, but people seem to confuse 'not knowing' with 'knowing not' -- if they don't know, they assume it's not important, and that doesn't seem right.


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## foz (Sep 30, 2004)

I can see the logic behind going for the stiffer crank if the weights were the same, but my question was more related to the fact that most of the tests seem to say that crank stiffness is more or less the same between most cranks. The whole 'stiffness' thing is pretty difficult to quantify for any given bicycle, because there are so many variables. Given that it´s much easier to measure a weight difference, and the effect it has on riding speed, why not take the proven advantage over the (more or less) unproven one?

And before anyone comes out to say that weight is not important, I´ll just say that the difference between an unloaded tourer at about 14kg and the same bike at 60kg fully loaded is huge. ok, so 100g from an already light 8kg race bike is not such a great difference, but it´s there.

foz


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## divve (May 3, 2002)

You're correct, most cranks are more than sufficiently stiff. There are a few borderline exceptions, however, such as the skinny Tune cranks.

If you're not _that_ concerned in regards to weight try to find something that both shifts well and is reliable. In the latter case the MegaExo option would be preferred over the rather spotty bearing reliability track record of traditional ISIS bottom brackets systems.


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