What is the truth behind bike weight? Does it really help THAT much?



::dom::

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sogood said:
PhillP: I hear you. But it stands in stark contrast to the ceramic bearing you are selling in your signature line. :eek:

That's why he's selling them :p ;)
 

oldbobcat

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Aug 31, 2003
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mikesbytes said:
Should I buy bike shorts because they are lighter than bib knicks?
And while you're at it, drill out your water bottles. Finally, somebody's talking sense here.
 

mikesbytes

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oldbobcat said:
And while you're at it, drill out your water bottles. Finally, somebody's talking sense here.
Good idea and I was thinking of using carbonated water, how stupid of me.
 

oldbobcat

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Crankyfeet said:
Y
It is the same reason why a guy gets a better start in a 100 meter sprint by pushing off rigid starting blocks as opposed to the same guy pushing off foam rubber blocks. Any deformation of the frame is work absorbed that is not being transmitted via the chain to the rear wheel.
Only thing is, riding a bike is not like pushing off starting blocks. It's about spinning the cranks as fast as possible, in as large a gear as possible, to make the drive wheel turn as fast as possible. Every sprint I've ever lost was to a rider who could increase his leg (crank) speed more more effectively than I could.
 

alienator

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oldbobcat said:
Only thing is, riding a bike is not like pushing off starting blocks. It's about spinning the cranks as fast as possible, in as large a gear as possible, to make the drive wheel turn as fast as possible. Every sprint I've ever lost was to a rider who could increase his leg (crank) speed more more effectively than I could.

It'd be fun if the people so religiously invested in the whole idea that stiffer is better would actually show how that is the case with numbers, facts, studies, equations. Alas, they don't because they can't. In fact, there are zero studies that show such results. Golly, you'd think with something so allegedly obvious, there'd be a simple study or two that would have verified those "stiff" assumptions.
 

::dom::

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mikesbytes said:
Good idea and I was thinking of using carbonated water, how stupid of me.
Even better. Don't fill the bottles. Imagine the weight saving 1 litre = 1kg :eek:
 

Crankyfeet

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alienator said:
It'd be fun if the people so religiously invested in the whole idea that stiffer is better would actually show how that is the case with numbers, facts, studies, equations. Alas, they don't because they can't. In fact, there are zero studies that show such results. Golly, you'd think with something so allegedly obvious, there'd be a simple study or two that would have verified those "stiff" assumptions.
Ah yes, the old, “You can’t have an opinion unless you have a scientific test with data to back it up” argument. In this view of the world, there are hundreds of global laboratories with scientists in white lab coats running around performing self-funded experiments, like Myth Busters, determining things such as: “Is a tight suspension in a car better for cornering than a soft, mushy one”. Or “Are stiff skis better than flexible ones for Olympic slalom skiers”. Or “Is it better to have a Styrofoam cup or a cardboard one with a sleeve around it for drinking hot coffee without burning your hand”.

Of course, if these frame stiffness tests were performed, they would most likely be completed in-house by a bike manufacturer, and the results most likely wouldn’t be published for public consumption. The results would be proprietary. Similarly if they were independently performed, they would most likely be funded by the owner of the results, and the results not made public.

But we do have a claim here of a test performed (by John Swanson) that found only a 0.05% difference between a “noodly” frame and an ultra-stiff one. So the stiffness is a factor according to these results, it’s just not a significant one. I requested to know how that test was performed in an earlier post. Getting data is a lot easier than perfectly simulating the biomechanics of the pedal stroke and swaying frame that occurs in the final sprint of a race. No disrespect to Mr. Swanson. His test could be flawless. But the data is only as good as the test.

Dave Kirk’s article on stiffness was cited before where he postulates that the effect of any elasticity in the frame is nullified because the frame has to return to its original position, thereby giving back what was lost. However this would be fine, if the pedal stroke was a constant force applied around the entire 360 degrees of one cycle. But it isn’t. The power zone occurs around the 3 o’clock – 9 o’clock position. If the frame deflects in the power zone and then retracts in the dead zone (around 6 o’clock – 12 o’clock), then there will not be the same effect. The retraction effect will just slow down your pedal stroke in the dead zone while little pedal force is being applied comparitively.

There are many possible points of deflection/elasticity that can lose power and response in the important power zone. The crank, the chain, the frame, your shoes and pedal connection, the wheel, even the tires can deflect (compress or elongate). If we take an extreme case where we have a crank that completely deflects when you push in the power zone (a "noodly" crank), then for your pedals to go around one full rotation, you will have to fight the crank wanting to return to its original straight shape as your feet are at the top and bottom of the stroke. It’s going to be hard going.

Ideally the drive train and frame would have a low enough deflection that it causes minimal loss in the power zone.

I am interested by John’s experiments. Unless I am grossly mistaken, I can conceive in theory that any deflection in the frame is going to contribute to power loss. The question is magnitude. John’s experiments seem to indicate it is insignificant. I’m interested in these results, because I’m as curious as anyone to get to the truth.
 

Phill P

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A simple question for those who have been riding for a few decades........

What would you rather ride?-

A bike that is as stiff and light as the one you have today (assuming it is a modern bike)
Or a bike as stiff and weighs the same as what you had in the 70s or 80s?

yeah drive train technology is a factor, but I know I feel faster on my modern mid range Al bike than on the cromo bike I had in High School (I wish I still had the energy I had back then though!!)

However I think stiffness is only a factor in some circumstances and become insignifacant in other, just like weight is only a factor in some circumstances and becomes insignificant in others.

No facts, just opinion.
 

sogood

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Crankyfeet said:
Dave Kirk’s article on stiffness was cited before where he postulates that the effect of any elasticity in the frame is nullified because the frame has to return to its original position, thereby giving back what was lost. However this would be fine, if the pedal stroke was a constant force applied around the entire 360 degrees of one cycle. But it isn’t. The power zone occurs around the 3 o’clock – 9 o’clock position. If the frame deflects in the power zone and then retracts in the dead zone (around 6 o’clock – 12 o’clock), then there will not be the same effect. The retraction effect will just slow down your pedal stroke in the dead zone while little pedal force is being applied comparitively.
Just curious if this can be tested directly given the availability of power meters. If one pairs up a SRM and a PowerTap, then should we be able to extrapolate a difference? Of course, the difference may get hidden by the noise of the two respective systems.
 

mikesbytes

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Phill P said:
A simple question for those who have been riding for a few decades........

What would you rather ride?-

A bike that is as stiff and light as the one you have today (assuming it is a modern bike)
Or a bike as stiff and weighs the same as what you had in the 70s or 80s?

yeah drive train technology is a factor, but I know I feel faster on my modern mid range Al bike than on the cromo bike I had in High School (I wish I still had the energy I had back then though!!)

However I think stiffness is only a factor in some circumstances and become insignifacant in other, just like weight is only a factor in some circumstances and becomes insignificant in others.

No facts, just opinion.
The lightweight steel frames of the 70's and 80's weren't a hell of a lot heavier than todays bikes, perhaps 1kg ?
 

alienator

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Phill P said:
A simple question for those who have been riding for a few decades........

What would you rather ride?-

A bike that is as stiff and light as the one you have today (assuming it is a modern bike)
Or a bike as stiff and weighs the same as what you had in the 70s or 80s?

yeah drive train technology is a factor, but I know I feel faster on my modern mid range Al bike than on the cromo bike I had in High School (I wish I still had the energy I had back then though!!)

However I think stiffness is only a factor in some circumstances and become insignifacant in other, just like weight is only a factor in some circumstances and becomes insignificant in others.

No facts, just opinion.

I'll bet the majority of riders would be hard pressed to determine, in a blind test, what they were riding and how stiff it was.

The memory of bikes past isn't conclusive of anything, except that memories aren't exactly viable quantitative or qualitative references.
 

Phill P

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I know its not the strongest data, but come on would you give up all your nice bikes for a 70s steel frame on race day?

I agree that most couldn't tell. I doubt I could tell during a spin around the block. I certianly couldn't tell the difference between two bikes that are close in stiffness.
However I'm 100kg plus and riding a square taper bb. I can remember riding another bike with hollowgram cranks and slighter more OS down tube, correct size for me. When in the big ring and a high gear trying to launch from stand still it felt stiffer, more direct.

Whether this was actually faster I don't know, but it felt better.

This was only during low rpms and max torque. I doubt it'd have the same to say spinning up a hill at 100rpm.
 

alienator

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Phill P said:
I know its not the strongest data, but come on would you give up all your nice bikes for a 70s steel frame on race day?

I agree that most couldn't tell. I doubt I could tell during a spin around the block. I certianly couldn't tell the difference between two bikes that are close in stiffness.
However I'm 100kg plus and riding a square taper bb. I can remember riding another bike with hollowgram cranks and slighter more OS down tube, correct size for me. When in the big ring and a high gear trying to launch from stand still it felt stiffer, more direct.

Whether this was actually faster I don't know, but it felt better.

This was only during low rpms and max torque. I doubt it'd have the same to say spinning up a hill at 100rpm.

There is a huge difference between "felt better" and actual performance benefit.

For the record, I can guarantee that you didn't feel any stiffness difference between a square taper BB and a Hollowgram BB. Don't forget that up until last year, Boonen was sprinting on square taper BBs.

There is zero evidence, i.e. nothing, that gives any hint that stiffness is an important performance parameter. Nada. Zilch. In fact no one has yet to even do a first order calculation of any sort that would even hint at the glory of stiffness.

Ride what feels good. That is good advice. However, don't mistake "feel good" for some physical reality.
 

jhuskey

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Oct 6, 2003
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alienator said:
There is a huge difference between "felt better" and actual performance benefit.

For the record, I can guarantee that you didn't feel any stiffness difference between a square taper BB and a Hollowgram BB. Don't forget that up until last year, Boonen was sprinting on square taper BBs.

There is zero evidence, i.e. nothing, that gives any hint that stiffness is an important performance parameter. Nada. Zilch. In fact no one has yet to even do a first order calculation of any sort that would even hint at the glory of stiffness.

Ride what feels good. That is good advice. However, don't mistake "feel good" for some physical reality.


I would agree that is hard to put an exact description on why one bike feels different than another but ultimately they do.
I find that I feel much better on decents on some bikes than others. Climbing? Maybe.
 

Crankyfeet

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ScienceIsCool said:
Yeah, I've worked out the numbers here in this forum a few times. The difference between a super stiff frame and a "noodly" frame (using measured frame stiffness) was less than 0.05% of Power. Or something like that. I can't be bothered to run the numbers again or look it up. So maybe 0.2 Watts at a big effort of 400 Watts.

In other words, the zipper on your jersey will probably have a bigger effect...

John Swanson
www.bikephysics.com
I'm more interested in the effects at 1200+ watts which is the often quoted power that pro sprinters such as Boonen are reputed to be applying in the final 250 yards of a race. And I wouldn't be surprised if the real effects are a non-linear relationship (exponential) to the force applied to the pedal. Call it instinct.. but that's how a lot of scientific tests begin... testing a hunch.

Also I'm quite interested by your ability to perform a controlled experiment and get a testing accuracy to 5/10,000 (0.05%). That's a very precise test for measuring changes in output without falling within the margin of error of the testing apparatus.
 

Crankyfeet

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alienator said:
There is zero evidence, i.e. nothing, that gives any hint that stiffness is an important performance parameter. Nada. Zilch. In fact no one has yet to even do a first order calculation of any sort that would even hint at the glory of stiffness.
So how do you support your antithesis that stiffness is a complete non-factor... if you are basing your opinion on no data obtained from any studies, experiments or calculations?
 

TheDarkLord

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Crankyfeet said:
So how do you support your antithesis that stiffness is a complete non-factor... if you are basing your opinion on no data obtained from any studies, experiments or calculations?
Maybe it is just a "hunch" of alienator? Just like the opinions/hunches of other people regarding bike weight? ;)
 

Crankyfeet

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TheDarkLord said:
Maybe it is just a "hunch" of alienator? Just like the opinions/hunches of other people regarding bike weight? ;)
The effect of bike weight is a relatively easy one to work out though without the need for empirical testing. Its high school physics/mechanics.

Without doing the calculations for various grades, bike+rider weights, and accelerations... I think it always comes down to a value judgment. If it is found that increased stiffness gets you to the line a foot quicker in a 200 yard mash sprint, or a two pound reduction in bike weight gets you to the top of a mile climb a few seconds quicker... some people/racers might want to spend the $$thousands on that improvement. For others... they might rather have the money.
 

TheDarkLord

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Crankyfeet said:
The effect of bike weight is a relatively easy one to work out though without the need for empirical testing. Its high school physics/mechanics.

Without doing the calculations for various grades, bike+rider weights, and accelerations... I think it always comes down to a value judgment. If it is found that increased stiffness gets you to the line a foot quicker in a 200 yard mash sprint, or a two pound reduction in bike weight gets you to the top of a mile climb a few seconds quicker... some people/racers might want to spend the $$thousands on that improvement. For others... they might rather have the money.
I agree. For a pro or a Cat 1 race, the very end where several tens of riders are in a mad sprint to the finish, things such as weight and stiffness may well be the key to ****** a podium spot. But for the ordinary rider, the difference is probably too small to make an appreciable difference - especially when the engine's performance has significant potential for improvement. In any case, one of the difficulties in testing is getting the control set up properly. The wattage output to the bike, and other factors have to be identical to really see how much improvement the stiffness provides, and I imagine that it is quite difficult under real conditions to disentangle the effect of stiffness from the miriad other factors which affect the final performance.
 

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