# New twist on "does weight really matter"?



## Lifelover (Jul 8, 2004)

I for one do not really care about how fast I can climb any given hill. I do however care about how far up any given hill I can make it before keeling over.

I have a constant debate with friends as to just how much weight (mostly wheel/tire weight) will help when climbing. All of us are clydes (I"m a super clyde) and my one friend who is around 225# has spent big bucks recently on lighter wheels (Zipps 303) in hopes that they will help him make it up the Assault on Mt. Mitchell in May.

So the question is:

How much of a reduction in work is there by having consderably lighter wheels when climbing? Has anyone with a SRM ever compared to power output for a same climb, at the same speed but with different wheels?


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## homebrew (Oct 28, 2004)

Lifelover said:


> I for one do not really care about how fast I can climb any given hill. I do however care about how far up any given hill I can make it before keeling over.
> 
> I have a constant debate with friends as to just how much weight (mostly wheel/tire weight) will help when climbing. All of us are clydes (I"m a super clyde) and my one friend who is around 225# has spent big bucks recently on lighter wheels (Zipps 303) in hopes that they will help him make it up the Assault on Mt. Mitchell in May.
> 
> ...


I do not have a power meter (I use heart rate) but my take is that we all have a cadance for climbing that works best. IMO a light bike/wheels does not make climbing less work, you just get more results (speed) . Physics aside, I ride hills with the max effort I can without blowing up. So my effort tends toward greater speed if givin a lighter bike setup. It depends on the grade as well. The greater the grade the more weight matters. If you get to the top a bit faster using the same power it would be some help but I think that your friend will still suffer. Good luck on your climb


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## Kerry Irons (Feb 25, 2002)

*Weight is weight*



Lifelover said:


> How much of a reduction in work is there by having consderably lighter wheels when climbing?


Going up a 6% grade, 1 lb (454 gm) weight reduction is worth about 0.03 mph (0.05 km/hr) for a 225 lb. (102 kg) rider on a 6% grade going 7.5 mph (12 km/hr). That is a gain of about 15 seconds per hour. It makes no difference whether that weight reduction is in the wheels or from ditching 16 oz (454 cc) of water.


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## SDizzle (May 1, 2004)

Kerry Irons said:


> Weight is weight


I would be more interested to see how/if said cyclist could compare his power output for his own bodyweight, at, say, 250 lbs vs 200 lbs. I'd guess the difference would be significantly more than the advantage gained by riding Zipp 303s and Veloflexes instead of Mavic DeeMaxs shod with 3" Gazzis run at 18 psi.


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## ukiahb (Jan 26, 2003)

*check out analytic cycling....*

at http://www.analyticcycling.com/ ....you can plug in the numbers and see how much (or little) differnce various changes make


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## homebrew (Oct 28, 2004)

ukiahb said:


> at http://www.analyticcycling.com/ ....you can plug in the numbers and see how much (or little) differnce various changes make


A usefull site however the lab boys fail to include all the variables of the road. We seldom climb at a steady rate. Many other factors are not considered 
Yes a 200lb rider will climb better then a 250 lb rider but the question was asked concerning bike/ wheel weight.
Wheel weight does matter more then any other weight, some time back I filled a good friends tubes 1/2 full with wated before a day of climbing as a joke. He will forever attest to lighter wheels being faster on climbs! Not science I know but it still shows that wheel weight matters most. I have made many improvements (ie lighter parts) on my bike over the years but wheels made the most improvement (other then getting fit). Try riding some heavy winter tires and then switch to some ultra light race tires. You will see that it matters more then a water bottle. Still as I said before this rider will still suffer and would as a practical matter be better off giving me the new set of wheels  Just my opinion, flame on


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## divve (May 3, 2002)

If you're not braking, wheel weight doesn't matter as long as the complete system weight remains identical. The laws of physics don't change due to varying climb rate or terrain changes. 

Just because a water bottle feels different compared to the same weight added to wheels doesn't prove anything either. To draw a parallel, would you rather be hit in the head by a 2lb pillow filled with feathers or a 2lb lead weight? They feel completely different, but I assure you they weigh the same.


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## filtersweep (Feb 4, 2004)

Kerry Irons said:


> Going up a 6% grade, 1 lb (454 gm) weight reduction is worth about 0.03 mph (0.05 km/hr) for a 225 lb. (102 kg) rider on a 6% grade going 7.5 mph (12 km/hr). That is a gain of about 15 seconds per hour. It makes no difference whether that weight reduction is in the wheels or from ditching 16 oz (454 cc) of water.


And what goes up must come down... I don't know that I'd really be loving the descent on a set of ultralight, low-spoke count wheels.


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## burlguy (Feb 19, 2005)

*numbers shmumbers , you ride the 4 pound wheels .*

After 55 miles of ups and downs today, (playing catch me if you can) Iam very happy that I purchased my light wheels . If I had gone with what I have read from the scientific community I would have been fine with my 4 lb set. Since my present set of wheels and tires saved me two pounds I have come to an interesting conclusion. I would have had to lift that 2 extra pounds 4000 feet (roughly the days climbing total). So for those that say weight doesnt matter much feel free to curl that 2 extra pounds 2000 times since you will roughly lift it two feet with each rep. And since this would be no real physical task for anyone in decent shape, do this while running 55 miles or walking and tell me if you get more of a workout. It is just pure nonsense to think that heavier wheels dont slow one down. Hmm, maybe all the pro teams have got it all wrong heavier wheels will help you carry more momentum going up the hills


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## Kerry Irons (Feb 25, 2002)

burlguy said:


> Since my present set of wheels and tires saved me two pounds I have come to an interesting conclusion.


Are you saying you have 900 gm wheels? You say your old wheels were 1800 gm, and you shaved 2 lb (900 gm), although you do allude to lighter tires. You could have changed to lighter tires (if those were most of your weight savings) on your old wheels. At any rate, I never said heavier wheels were just as fast - the OP asked how much less effort it took, and I presented the numbers. Simple as that. What I sense in your post is that you feel great about your lightweight wheels and that you take offense at anyone who suggests they are not a huge improvement over what you had. This has nothing to do with science.


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## homebrew (Oct 28, 2004)

divve said:


> If you're not braking, wheel weight doesn't matter as long as the complete system weight remains identical. The laws of physics don't change due to varying climb rate or terrain changes.
> 
> Just because a water bottle feels different compared to the same weight added to wheels doesn't prove anything either. To draw a parallel, would you rather be hit in the head by a 2lb pillow filled with feathers or a 2lb lead weight? They feel completely different, but I assure you they weigh the same.


Well, IMO yes it does, you loose momentum when the hill gets harder or you hit a rough patch of tarmac. Light wheels being need somewhat less force to get back up to speed.
It also matters were the weight comes from, the bike frame is static but wheels turn. The riders extra weight does produce extra watts. It is true this extra wattage is not likely to gain in climbing however the extra weight on the frame give no advantage in power. 
If a machine powered you up a perfect ramp at a steady pace you would be correct in your statement regarding the physics. IMO however your model falls short. I hope I explained this in an understandable manner


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## LeGrimper (Dec 1, 2001)

*rotational weight?*

what about rotational weight kerry?

Those wheels are spinning are they not?


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## burlguy (Feb 19, 2005)

*Numbers dont tell the whole story ....*



Kerry Irons said:


> Are you saying you have 900 gm wheels? You say your old wheels were 1800 gm, and you shaved 2 lb (900 gm), although you do allude to lighter tires. You could have changed to lighter tires (if those were most of your weight savings) on your old wheels. At any rate, I never said heavier wheels were just as fast - the OP asked how much less effort it took, and I presented the numbers. Simple as that. What I sense in your post is that you feel great about your lightweight wheels and that you take offense at anyone who suggests they are not a huge improvement over what you had. This has nothing to do with science.



I went from 1850 gram set of wheels to a 1330. I went from a 260g tire to a 160g. On the wheel weight I included the cassette switch Ultegra to Dura. Oh and lightweight tubes. I guess it could have been over two pounds saved.

No offense taken . I just see so many write ups saying how little weight reduction helps. This is just utter nonsense. Feet climbed and distance traveled is always easier with less weight. The power out put you take into consideration is not the "effort". It takes such and such amount of power to rotate this wheel with this given weight of rider does not equal the effort. I dont think mathematics makes this simpler even though it can be applied such as my last post. The effort is power output in total, not at any given instance . It is rather dependent (to measure expected gain) on distance, and elevation climbed. The variables are also ,rotational weight and bike weight and speed. Lighter wheels = Better climbing . One pound is only worth 15 seconds on the hour ? This does not take into consideration rider weight versus bicycle weight . And the amount of effort and threshold of fitness . There is no way in my own opinion to tell some one that a lighter set of wheels is not going to make a substantial difference.


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## LeGrimper (Dec 1, 2001)

*think of it as kj's*

A few years back I went from heavy(er) DA/OPs to AMC350's and there is a considerable difference in energy and handling.

If they save a few watts, which may not be that noticable on a single climb, think of the kj's (or calories) it would save over, say, 3 hours and 1500 meters of climbing.

Anyone care to plug in the math on that one? 500g saved over 3 hours and 90kms with 1500 meters of climbing at an average cadence of 85 rpm.


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## Coolhand (Jul 28, 2002)

If you follow some of the coaching lists and recent papers on aerodynamics and cycling performance, the limitations of the analytic site with regard to stocastic (spelling is way off- sorry) inputs is exposed. Additionally, the scientific study detailed in the USCF coaching manual (it's at home, or I would cite the study), long 6% grades were the only area that lighter weight *was* found to make a significant impact in overall time- showing a much greater improvement then Kerry did. So in that rather limited situation, the light weight does help. In every other situation, improved training (up to Pro 1, 2 class of course, were proper training is already utilized more often then not) and superior aerodynamic performance are the key.

Additionally, the "take less water" agrument is basically flawed, as you can do that with lighter wheels too. I know, that's crazy talk- but it's true! Same thing with the sad tired cliche about going to the bathroom first (like anyone was neglecting to go because they were riding the carbon wheels that day). 

- Back to the wheels point. The reason the wheel weight matters more on the 6% and above long mountain climbs is that much lower average speed riders reduces the impact of aerodynamics for once. That is why the special climbing bikes, wheels, ditching water bottles ect are common on major mountain stages. Weight reduction is key in that limited set of facts.

In most non-hill climb situations, aerodynamics, and not weight or moment of intertia issues, plays the major role in improving performance. This is one of the reasons Mavic's Cosmic Carbones are used more by Mavic sponsored racers then the light Krysruims (spelling again) models, despite weighing 200+ grams more. 

Now, for the case of our Super Clydes and the big long hills. Well, you are doing both long climbs and plenty of distance and speed so aero will play as big a role as weight. However, the 303's do pretty well on both (assuming you are talking the tubular versions- the clinchers are porky little pigs). However, the 404 pave's or clydesdale version would have been better choices as they gain very little additional weight, while improving the aerodynamics, stiffness and durability. 

Of course, dropping any body fat based weight would help buckets too, but I figured that was obvious enough not to belabor the point.


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## Kerry Irons (Feb 25, 2002)

*Understanding physics*



homebrew said:


> you loose momentum when the hill gets harder or you hit a rough patch of tarmac. Light wheels being need somewhat less force to get back up to speed.
> It also matters were the weight comes from, the bike frame is static but wheels turn. If a machine powered you up a perfect ramp at a steady pace you would be correct in your statement regarding the physics. IMO however your model falls short. I hope I explained this in an understandable manner


Sorry to say this, but what you explained is your misunderstanding of the physics. You have made absolutely correct statements, but by stating only half of the equation, you propagate error. Yes, lighter wheels are easier to accelerate, AND rotating weight is different than static weight. However, what you ignore is that lighter wheels also DEcelerate faster than heavier wheels. 

The weight in rims/tires are effectively flywheels. When you encounter a steeper section, a rough patch of road, a gust of wind, or are continuously surging your speed due to pedalling up a steep section, you ARE constantly accelerating and decelerating. Those who want to believe that lighter wheels are somehow more significant than other weight savings concentrate on how much easier they are to speed back up in each of these cases. They somehow ignore the fact that these same wheels slow down more in each situation, since they are carrying less momentum into each slowdown. Due to conservation of momentum, the savings of easier acceleration are canceled by the extra speed losses. 

The most important application for lightweight wheels is in a criterium, where you brake and accelerate for each corner. Here, you are not conserving momentum, you are burning it up with braking. Otherwise, weight is weight and savings due to lighter tool bags are the same as those from lighter wheels. 

Just for reference, 1500 meters of climbing is 4,900 feet. The effort of lifting 1 lb. 4900 feet spread over 3 hours requires 0.0008 horsepower, which is 0.62 watts which equals about 2 calories per hour (assuming a 24% efficiency of the human body). A 225 lb rider climbing a 6% gade at about 7.5 mph is burning about 880 calories per hour. Shaving 1 lb. off the wheels, the bike, or the rider will reduce this effort by about 4 calories per hour or allow a 0.03 mph speed increase at constant power output. That speed difference equals a gain of 13 seconds per hour - the lighter rider goes 142 feet farther every hour.


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## Kerry Irons (Feb 25, 2002)

*Want to see that study*



Coolhand said:


> the limitations of the analytic site with regard to stocastic (spelling is way off- sorry) inputs is exposed. Additionally, the scientific study detailed in the USCF coaching manual (it's at home, or I would cite the study), long 6% grades were the only area that lighter weight *was* found to make a significant impact in overall time


I can't figure out what is meant by "stochastic inputs." Stochastic means random or non-quantifable. Lifting weight at a given rate is an EXTREMELY simple physics calculation - watts/horsepower is weight times height over time. I would be very interested in any study that shows an impact of weight reduction in climbing beyond what Newtonian physics would show. Please look this up when you get home and post it here.


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## Kerry Irons (Feb 25, 2002)

*Kinetic energy*



burlguy said:


> I just see so many write ups saying how little weight reduction helps. This is just utter nonsense. Feet climbed and distance traveled is always easier with less weight. The power out put you take into consideration is not the "effort". It takes such and such amount of power to rotate this wheel with this given weight of rider does not equal the effort. The variables are also ,rotational weight and bike weight and speed. Lighter wheels = Better climbing . One pound is only worth 15 seconds on the hour ? This does not take into consideration rider weight versus bicycle weight . And the amount of effort and threshold of fitness.


As noted in other posts, the physics calculations are simple. I can never figure out how people "see" faster climbing than physics will allow. Wheels (specifically rims and tires) require double the Kinetic Energy (KE) to accelerate compared to other weight because there is the KE to move them down the road and to spin them up to speed. However, once they are spun up, that KE is "stored" and does not affect total energy requirements until speed changes. If you speed up, you need to store more energy in rotating the wheels, and if you slow down, you get that stored energy back.

I can't understand how power is not equal to effort. I don't understand why you need to consider rider weight separately from bike weight. I don't understand what "amount of effort and threshold of fitness" means. When you lift a weight a given height over a defined amount of time, the effort required (and the calories expended) is easily determined. Saying that somehow the physics changes because that weight is rotating is nonsense. If you hung a wheel from a crane and measured the amount of effort (power, watts, calories) required to raise it at a certain speed, the amount of power would not change if that wheel was spinning or not. Somebody PLEASE explain the "alternative energy path" that would explain things differently.


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## Coolhand (Jul 28, 2002)

> Just for reference, 1500 meters of climbing is 4,900 feet. The effort of lifting 1 lb. 4900 feet spread over 3 hours requires 0.0008 horsepower, which is 0.62 watts which equals about 2 calories per hour (assuming a 24% efficiency of the human body). A 225 lb rider climbing a 6% gade at about 7.5 mph is burning about 880 calories per hour. Shaving 1 lb. off the wheels, the bike, or the rider will reduce this effort by about 4 calories per hour or allow a 0.03 mph speed increase at constant power output. That speed difference equals a gain of 13 seconds per hour - the lighter rider goes 142 feet farther every hour.



That is the problem, when the physics applied is too simple and not reflective of the actual conditions to be measured I believe was the argument against knee jerk reliance on back of the envelope calculations which are not peer reviewed. 

Here is the peer reviewed scientific journal citation:

Jeukenrup, AE and Martin, J. _Improving Cycling Performance: How Should We Spend Our Time and Money_ *Sports Medicine* 31(7): 559-569, 2001. 

From the 2005 USA Cycling Club Coach Manual, directly citing the study (the manual is reviewed itself by most of the coaching luminaries in the USCF):

"What about going uphill? Wouldn't a lighter bike and/or weighing less make a difference? Of course! It is nice when science supports what we think to be true. On a 3% grade on a 20km TT, the authors determined that reducing bike weight by 3KG would result in a time savings of 94, 42 and 29 seconds for the Novice, Well Trained and Elite Cyclists. Increasing the grade to 6% yields savings of 3:38, 1:52 and 1:15 for the Novice, Well Trained and Elite Cyclists, respectively."

The peer reviewed numbers seem much different then yours. Maybe your model needs some work, as the differences seem to be much greater than you predicted- but they did use greater weight delta's on weigh change- but not nearly enough for the difference shown. 

The journal study is quite interesting, detailing the improvements of using a Carbohydrate Beverage, Caffeine, Lighter bike in a flat TT, Lighter Bike in a uphill TT of two different grades, aerp positioning in a TT, using an aero bike frame, improved interval training methods, ect. Really interesting stuff- well worth getting the training materials for.


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## divve (May 3, 2002)

I read bike weight but don't see wheel weight specifically singled out?


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## TurboTurtle (Feb 4, 2004)

Coolhand said:


> That is the problem, when the physics applied is too simple and not reflective of the actual conditions to be measured I believe was the argument against knee jerk reliance on back of the envelope calculations which are not peer reviewed.
> 
> Here is the peer reviewed scientific journal citation:
> 
> ...


Couple problems I have with this:

First, being a 'USCF coach' does not qualify one to do a 'peer review' of a scientific article.

Second, from what I get out of the abstract, this is just another mathmatical model. Why do you condemn one model and proclaim another as fact? It's just a model. All models have problems in the real world.

TF


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## Kerry Irons (Feb 25, 2002)

*This cracks me up! *



Coolhand said:


> That is the problem, when the physics applied is too simple and not reflective of the actual conditions to be measured I believe was the argument against knee jerk reliance on back of the envelope calculations which are not peer reviewed.
> the authors determined that reducing bike weight by 3KG would result in a time savings of 3:38, 1:52 and 1:15 for the Novice, Well Trained and Elite Cyclists, respectively." (6% grade).
> 
> The peer reviewed numbers seem much different then yours. Maybe your model needs some work, as the differences seem to be much greater than you predicted- but they did use greater weight delta's on weigh change- but not nearly enough for the difference shown.


Man, nothing like seeing what you want to see! I estimated 13 seconds saved per hour, stating rider weight, power output, and speed. Those numbers are not listed in the abstract, but assuming a much lighter rider and higher output, one hour is not far off what an elite rider could do a 20km TT at a 6% grade. Taking the much higher weight differential in the article (6.6 lb.), you get about 85 seconds saved (6.6 x 13). The article quotes between 75 and 112 seconds. It seems to me that my numbers are just about identical with the ones in the article! 

BTW it is not "my" model. The model was published in 1974 (Bicycling Science, Whitt & Wilson, MIT Press) and many times and places since. It is based on the fundamentals of physics with measured factors for friction and aerodynamic drag incorporated, nothing more and nothing less.

The problem with 1) not understanding the physics and 2) wanting to believe something other than what physics can easily tell us is that you latch onto numbers that you think prove your point when in fact they do not.


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## burlguy (Feb 19, 2005)

*Rider Fitness*

This is what is being left out amongst other things . A rider with less physical fitness is going to benifit greater from an decrease in bicycle weight. The typical rider while struggling up a grade will need every advantage he can becuase of the power to weight ratio. He can only put out so much effort and then bonk. If that same rider has two less pounds on his bicycle and can maintain the same effort because of lighter rotational or bike weight than the difference benifit is no longer measurable just by calories burned but by distance traveled and velocity. Power to weight ratio, and effort . Any honest person can tell when they get on a lighter bike how much easier it is to pedal and climb . Anything else is a lie.

There is no alternate energy path in this description or my past post . There are however some things missing in the equations posted previously that arent mine . Just some oversights Iam sure.  There is no great mystery even though we sure like to make one .


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## Coolhand (Jul 28, 2002)

TurboTurtle said:


> Couple problems I have with this:
> 
> First, being a 'USCF coach' does not qualify one to do a 'peer review' of a scientific article.
> 
> ...


Well, no it doesn't. Pretty sure I *never* said that. The article itself was reviewed by then published in a peer reviewed journal. The study is relatively well known and discussed in various coaching books.

See below for more details- and Kerry's and my numbers are alot closer once I fixed my conversion mistake (never do it from memory!!)


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## Coolhand (Jul 28, 2002)

Kerry Irons said:


> Man, nothing like seeing what you want to see! I estimated 13 seconds saved per hour, stating rider weight, power output, and speed. Those numbers are not listed in the abstract, but assuming a much lighter rider and higher output, one hour is not far off what an elite rider could do a 20km TT at a 6% grade. Taking the much higher weight differential in the article (6.6 lb.), you get about 85 seconds saved (6.6 x 13). The article quotes between 75 and 112 seconds. It seems to me that my numbers are just about identical with the ones in the article!


Ack, I screwed up the pounds to kilograms conversion. Grrrrr! 

Well at least I didn't crash my really expensive Mars probe because of it.


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## Lifelover (Jul 8, 2004)

*Screw all the math!*

Couldn't you just do what I asked to prove it one way or the other.

" Has anyone with a SRM ever compared to power output for a same climb, at the same speed but with different wheels?"


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## AJS (Aug 7, 2003)

burlguy: _"Any honest person can tell when they get on a lighter bike how much easier it is to pedal and climb ."_

To an extent, I agree with that, but not with the "anything else is a lie" part.

However, even with good formulae, something can still go missed or unaccounted for. Varying rates of friction loss between bikes, varied amounts of power actually delivered to the pavement from shoe to the rear tire from "flexing" losses of the entire drivetrain (power transfer efficiency), etc.


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## LeGrimper (Dec 1, 2001)

*slowly, slowly you are making the point.*

.[/QUOTE]Just for reference, 1500 meters of climbing is 4,900 feet. The effort of lifting 1 lb. 4900 feet spread over 3 hours requires 0.0008 horsepower, which is 0.62 watts which equals about 2 calories per hour (assuming a 24% efficiency of the human body). A 225 lb rider climbing a 6% gade at about 7.5 mph is burning about 880 calories per hour. Shaving 1 lb. off the wheels, the bike, or the rider will reduce this effort by about 4 calories per hour or allow a 0.03 mph speed increase at constant power output. That speed difference equals a gain of 13 seconds per hour - the lighter rider goes 142 feet farther every hour.[/QUOTE]

Just for reference, 1500 meters of climbing is 4,900 feet. The effort of lifting 1 lb. 4900 feet spread over 3 hours requires 0.0008 horsepower, which is 0.62 watts which equals about 2 calories per hour (assuming a 24% efficiency of the human body). 

So what is this in kj? 

What would light wheels save the pros in the TDF, over 3 weeks through the Alps and Pyrenees? 

If light wheels are easier to REPEATEDLY spin-up on big efforts (i.e. attacks on hills) but decelerate quicker (and you are now in the front group and on a wheel, saving 30% by drafting, and ready for another uphill surge) is this not exactly the point? A little bit of light peddling downhill and/or drafting is more desirable than trying to spin up heavy wheels during uphill attacks or tempo riding.

Lighter tires would also have lower rolling resistance too.

Light and Aero wheels (Zipp 404 or similar) are surely the best of all worlds.

And despite all the math what would you rather ride, a set of 1300g deep carbons or a 2.5 kg set of Velocity Deep V's with heavy hubs and 25mm tires? 

Hell, why not ride bomb proof 3 kg wheels? Infact why are the light carbons proving so popular?


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## AJS (Aug 7, 2003)

LeGrimper said:


> .
> 
> Lighter tires would also have lower rolling resistance too.
> 
> And despite all the math what would you rather ride,...and 25mm tires?


Hey wait a minnit! We've already gone through the lighter/wider tires vs. RR thing about 150 times. Try the search function.

Yes, I would rather ride 24s/25s or even up to 28 than 23s or less, and do. They just work better for my weight and the crappy road conditions where I live, and that's more important than the small weight penalty.

Anyway, back to the debate...


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## divve (May 3, 2002)

The point of contention is, your bike is both the minimum weight with the light wheels or heavy wheels. In that instance, the difference in performance is negligible. That's what the discussion is about and not whether your bike is easier to climb now that it's suddenly a few kilos lighter. We all know that's true.


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## Anti-gravity (Jul 16, 2004)

burlguy said:


> If that same rider has two less pounds on his bicycle and can maintain the same effort because of lighter rotational or bike weight than the difference benifit is no longer measurable just by calories burned but by distance traveled and velocity.


This statement makes no sense. Calories burned is not equal to the work needed to summit a hill, but it is _proportional_. Distance and velocity are constraints of work and energy (total energy is the sum of kinetic and potential energy, they simply add because they are scalar quantities.). If you want to go faster up the hill, you increase your energy output, or decrease the work needed (lightening the rider/bike). Same goes for increasing distance traveled. Calories burned is a good way to gauge performance increases as a result of decreasing weight or improved fitness.



> There is no alternate energy path in this description or my past post . There are however some things missing in the equations posted previously that arent mine . Just some oversights Iam sure.  There is no great mystery even though we sure like to make one .


Kerry's math is sound from what I can tell (I'm a physics undergrad currently, so I know a thing or two about mechanics). His math is simplified (does not include frictional and air resistance operators), but that is perfectly fine. All we are doing is comparing two different systems (in this case a lighter rider/bike with a heavier one) with similar constraints, so we can simply leave out frictional forces and air resistance from both of them. 

To say math is irrelevant or less important than your intuition breaks down the system of deductive thinking that forms the basis of our knowledge about how a bicycle works in the first place. Perception and actual results are two different things. I won't argue that your bike feels faster to you, but physics is our best tool for understanding the tangible differences in performance. The only time this discussion gets shrouded in mystery is when people spread ignorance and psuedo-science statements that end up confusing everyone.


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## AJS (Aug 7, 2003)

Anti-gravity said:


> To say math is irrelevant or less important than your intuition breaks down the system of deductive thinking that forms the basis of our knowledge about how a bicycle works in the first place. Perception and actual results are two different things. I won't argue that your bike feels faster to you, but physics is our best tool for understanding the tangible differences in performance. The only time this discussion gets shrouded in mystery is when people spread ignorance and psuedo-science statements that end up confusing everyone.


All true. 

But I think it is just as problematic to rely _only_ on specific math formulae for such a complex problem that do not address the other relevant variables. At the same time, we have to keep in mind that it is often the case that we're simply unaware of some variables, or unaware that they may affect the outcome to a greater degree than we initially assume.


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## Kerry Irons (Feb 25, 2002)

*Conversions*



LeGrimper said:


> So what is this in kj? What would light wheels save the pros in the TDF, over 3 weeks through the Alps and Pyrenees?


For reference, 1 hp-hr = 641 "calories" delivered to the pedals, 1 hp = 746 watts, 1 calorie = 4.186 kj. Here, all calories are kg-calories, "big" calories, or "food calories." The human body runs at about 24% efficiency so to deliver 1 hp to the pedals requires the body to consume 2700 calories, more than 4 times the 641 "calories" delivered to the pedals. Saving 4 calories per hour (that 13 seconds for a 225 lb./102 kg rider) means saving 16.7 kj.



LeGrimper said:


> If light wheels are easier to REPEATEDLY spin-up on big efforts (i.e. attacks on hills) but decelerate quicker (and you are now in the front group and on a wheel, saving 30% by drafting, and ready for another uphill surge) is this not exactly the point? A little bit of light peddling downhill and/or drafting is more desirable than trying to spin up heavy wheels during uphill attacks or tempo riding.


One more time, I've never said that lighter wheels (or lighter anything else) was not faster in climbing, or on the flats for that matter. I'm just attempting to quantify it for people who want to claim much greater improvements than are realistic. If I were in a race, particularly racing as a pro, gaining 13 seconds (from a 450 gm weight reduction) on every climb would be signficant, and that amount of time on the final climb would be a major advantage. And wheels that are easier to spin up are an advantage as well. The key point is not that there is no advantage, just that far too many people claim the advantage is far larger than it really is.

However, don't confuse yourself with the drafting argument. The savings from drafting at climbing speeds are minimal - nowhere near 30% and even it if was 30%, it would be 30% of a small number. Recovery after catching a surge comes from riding at a lower pace, not substantially from drafting.



LeGrimper said:


> And despite all the math what would you rather ride, a set of 1300g deep carbons or a 2.5 kg set of Velocity Deep V's with heavy hubs and 25mm tires? Hell, why not ride bomb proof 3 kg wheels? Infact why are the light carbons proving so popular?


See my comments above. The tradeoff we must make comes in cost and durability. Each useful increment of weight reduction brings significant cost and proable loss in durability. Each rider must decide whether it is "worth it" to go lighter, and that is the question that is frequently posed. It's easy to determine the added cost, and there are many reports on the reduced durability - I'm trying to clarify what "value" is obtained in terms of performance improvement.


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## Kerry Irons (Feb 25, 2002)

*More clarity*



Anti-gravity said:


> math is simplified (does not include frictional and air resistance operators), but that is perfectly fine.


Actually, the equation: calories/hr = [Vg*W(.0053 + %G/100) + .0083(Va^3)]*7.2 does indeed include friction and air resistance. Here, Vg is ground speed in mph, W is weight in lbs., %G is grade, Va is speed through the air in mph. The 0.0053 constant is a lumped parameter that includes tire friction, bearing friction, drivetrain friction, etc. and is based on measured data for lightweight bicycles. Likewise, the 0.0083 constant represents the drag coefficient of the wheels, rider, bike, etc. and is based on an "average" rider on a standard road bike. This constant is reduced when various aero equipment is used. The equation recognizes all of the physical factors experienced by a rider going down (or up) the road.

The example I gave of lifting a given weight a given height over a given distance simply isolated that element from the rest of the equation (it is the W*%G/100 calculation). The 13 second time saving used the total equation and so considered friction, aero drag, and work against gravity.


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## AJS (Aug 7, 2003)

Kerry Irons said:


> The tradeoff we must make comes in cost and durability. Each useful increment of weight reduction brings significant cost and proable loss in durability. Each rider must decide whether it is "worth it" to go lighter, and that is the question that is frequently posed. It's easy to determine the added cost, and there are many reports on the reduced durability -


And THAT is where the real problem lies! Good point.


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## LeGrimper (Dec 1, 2001)

*Is the right answer!!*

Kerry, what you wrote above is a good answer and covers the whole thread nicely. It is a joy to behold your work. Sound stuff and grounded firmly in reality.

So you are not confused, the 30% drafting is not up hill, but on the valley roads or flat after the climb where you did not get backed off by the 13 sec you calculated.

Drafting uphill is less than 30%, yes, you are going slower, but I think at todays pro speeds it is still significant with regards to energy (i.e. a 4 or 5% slope, say).

Is the price worth it? Well if you have made it to Europe and are racing UCI events in, say, Italy or France, Trentino springs to mind, then I think so, the cost of getting there and the sacrifices far outweighs the cost of a few sets of race wheels.

And if you have the money to treat yourself to these toys and you want to then why not go for it? 

Cycling hey?


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## AlexCad5 (Jan 2, 2005)

burlguy said:


> I went from 1850 gram set of wheels to a 1330. I went from a 260g tire to a 160g. On the wheel weight I included the cassette switch Ultegra to Dura. Oh and lightweight tubes. I guess it could have been over two pounds saved.
> 
> No offense taken . I just see so many write ups saying how little weight reduction helps. This is just utter nonsense. Feet climbed and distance traveled is always easier with less weight. .


 I live in a hilly area and ride about 5000 miles a year. My riding weight is 155lbs+/-.
I've been riding on AC 420's and Ksyrium Elites interchangably for the past year and a half. The K. elites are about a lb heavier. I honestly cannot tell the difference in weight from ride to ride, switching the wheels out. I change tires. Heavier ones, lighter ones. I can tell the difference in grip, in ride quality, but not in weight, regardless of the climb.

Some wheels seem to spin up faster than others. Deep wheels get blown around and cause steerage problems. I've got a Am 350 up front now, partially for that reason. But weight making a noticable diffence in a climb? Not in my book.
I like having a light bike because I get some kind of perverse joy when I pick my bike up in the garage to turn it around and I'm surprised how light it is. But I don't fool myself into thinking that it's making me fast. I have to earn that the hard way.

But that's just me, your experience may be different.


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## germplayer (Jan 6, 2005)

Kerry Irons said:


> Going up a 6% grade, 1 lb (454 gm) weight reduction is worth about 0.03 mph (0.05 km/hr) for a 225 lb. (102 kg) rider on a 6% grade going 7.5 mph (12 km/hr). That is a gain of about 15 seconds per hour. It makes no difference whether that weight reduction is in the wheels or from ditching 16 oz (454 cc) of water.


Hmm... Anybody know the weight difference between tap water and the more expensive kinds, like Propel or Evian?


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## atpjunkie (Mar 23, 2002)

*carbonated water is lighter*

bubbles baby bubbles

as another superclydesdale he should drop as much bodyweight as possible. as a beast unless you are sub 10% bodyfat cutting grams and the expense of strength and durability is money poorly spent.
so lose 1% and that's 2.25 lbs 1008 grams. lose 2% and you've just dropped nealy 5 lbs.

if you are 18% body fat and you lose to down 10% (225 to 207) thats 18 lbs or the weight of an entire bike. your power to weight will also surge.


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## campyhag (Feb 4, 2004)

Isnt it true that every pedal stroke is a lot of accelerations? It seems that we are assuming every pedal stroke has an exact amount of power through each part of the stroke. Doesnt this skew the pure physics arguement ? Not even Lance pedals perfectly even amounts of power through the entire pedal stroke. Just a question, my physics is very rusty...if its true though then lighter wheels would matter more than Kerrys examples illustrate...


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## jaldridge (Feb 27, 2005)

Kerry Irons said:


> Lifting weight at a given rate is an EXTREMELY simple physics calculation - watts/horsepower is weight times height over time.


 The problem with this is that a cycling system is not a simple, isolated physics system in which power (work per unit time) is simply measured by multiplying force (weight) by distance and dividing by time. Biomechanical systems are complex and the mechanical (bike) system is also complex. The simple watts = (newtons x meters)/seconds is an insufficiently subtle model.


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