Truthful, funny and entertaining post. Yes we humans are highly impressionable. :)

None of the theoretical explanations violate the 2nd Law. Everyone accepts that some useful energy is lost to friction, but that amount is extremely small.


And again, we can't evaluate any of these theories without hard data. (I'd also say that since Giant included that claim in marketing materials for a $10,000 bike used by pros, they believe it applies at very high wattages.)


Have you really not noticed how they publish data about aerodynamic advantages?

E.g. here's a whitepaper from Cervelo: http://www.cervelo.com/media/docs/Ce...cddcd4f6-0.pdf They quantify differences in drag, discuss methodologies and yaw selections, explain the relevance in detail... all over a one minute savings on a 60 mile ride.

If they aren't doing the same for frame stiffness, there has to be a reason.


It can -- and is -- measured by third parties, like Velonews, Procycling and Roues Artisanales.


Bike manufacturers do publish lateral stiffness numbers. So obviously, they don't think this will confuse anyone, and do think it will sell bikes. The buzzwords "laterally stiff" and "vertically compliant" have been in use for years now.


They do not make custom frames for riders. UCI rules don't allow it. Any bike used in the pro peloton has to be commercially available, even if it's insanely expensive and/or in limited numbers (e.g. McLaren Venge).

In addition:
1) What benefits a 2100-watt monster like Greipel may not benefit other riders. (Which is why you see lots of Tarmacs and few Venges.)
2) What benefits a 2100-watt monster like Greipel may not benefit Joe Average.
3) There are other reasons why a rider might choose a stiffer frame.
4) None of this answers the unproven question of "does a stiffer frame transfer power better?"


No, it really hasn't. Pros have believed a lot of things over the years that have turned out to be wrong.

What it says is that pros happen to like stiff frames. That doesn't prove that power output is improved.

So does the stiffer frame, and since smaller amounts of energy are transferred, smaller amounts of energy are lost.

1. Assertion with no supporting evidence
2. Also applies to any frame no matter what the stiffness is

Another assertion with zero supporting evidence.

Yeah, but... impedance mismatch

OP, just curious, has anybody provided any empirical data yet? No way I can read through this kind of stuff.

All the claims being made for how a frame that's really flexy stores and returns energy also would apply to a stiffer frame as well.

But the stiffer frame:

1. Transfers more energy directly to the drive train because it doesn't store it in the first place (and then HOPE it can return it to the drive train later...)
2. Doesn't lose as much in the energy transfers.

Claiming a flexier frame doesn't lose more energy is like claiming you've found a perpetual motion machine.

Nope.
But still civilised discussion all along :thumb:

That's the debate ... How does being stiffer get more power to the drivetrain ??
A stiffer frame flexes less, but isn't the same amount of energy wasted in trying to flex the stiffer frame ? You just don't realize it. X amount of energy goes to the wheel, and Y amount goes to lateral force on the frame. A stiffer frame resists the force better, but it is still there.

Nope.

No. The stiffer frame does not waste the same amount of energy.

If you assume the force the cyclist generates is independent of how much the frame flexes, the smaller flex means less energy is transferred. Period. End of discussion.

Because energy is force times distance.

No, it isn't. Because everyone accepts that the spring loses some energy to friction. The point is that any energy lost that way is so small, that it's inconsequential.


Again:

1) Theoretically, all of the stored energy that is not lost to friction does go back to the drivetrain (albeit indirectly).
2) Without hard data to back up these claims, stating categorically that "X is true" begs the question.

This reminds me of bokeh arguments on photography forums. In the end, the better frame/bike is the one you personally like more and that very well could be the flexier frame. There is such a thing as too stiff in bicycle design.

Won't get into a protracted aka convoluted? :) debate on a bike forum over the second law of thermodynamics...my major in college...lol.

As to a given pro's belief relative to given cause/effect that begets a particular paradigm. Points in time have little relevance, but long term trends tend to matter however aka the migration over time toward stiffer frames which have become available due to evolving technology.

There are no flexy bike in the pro peleton for good reason. Also chicken and egg. Why do pros prefer stiff frames at the exclusion to comfort? Simple..they are faster. Just like most pros don't ride with beach cruiser handlebars due to aero drag. :)
Btw, your assertion is wrong. Power output isn't improved in any frame scenario. This would violate the 2nd law of thermodynamics. Stiffer frames more efficiently transfer 'existing power' generated by the rider to the wheels which translates in higher road speed.

You do make one good point however. Why does the marketing department of Cervelo publish aerodynamic nos. for their frames? Calculus is based on selling more bikes because if it weren't it would be pure intellectual property. I believe the reason is, the difference is more quantifiable with drag nos. versus stiffness nos. In other words, the magnitude difference is greater than the small stiffness difference from a Cervelo R3 to S5 and hence this data manifests a greater perception of improvement underscoring an aero benefit. None-the-less a good point.

Same argument on audio forums. :)

Who said it is inconsequential? You. You versus all of pro cycling. Where's your data?..lol.

Prove it. Because my belief is that the frame flexes less per X input, but the rider is still putting X input laterally. Just like a stiffer spring will compress less for a given force, but that doesn't mean because it compresses less that less force was applied.

I repeated it a few times for you. Let me know if that actually ends things.

Sure. Now show me where spring rate is in that formula. You know, since frame stiffness is the actual point of contention in this thread, not high school physics.

It has to go somewhere, but how do you justify that it all goes back to the drivetrain? Assuming by friction you mean just the internal friction from the deformed frame material. This is the point of the theory where I stumble. I don't see why the return or some of it can't be against pressure exerted by the leg muscles. Maybe friction is increased at the bearings as the flex torques pedal axle. Or the twisting contact patch of the tire (as the deforming changes angle of the wheel) scrubs energy as friction heat and tire deformation.

Uh...no! Did you expect them to?:)

Just the usual lingo for imperfect nature of a spring in the real world. E.g. a compressed and released spring doesn't oscillate forever. You could think of friction as molecular or metal crystal interaction. Hysteresis is the technical term that encompasses all causes of loss, right?

tl; dr

My OPINION based on personal experience is that stiffness has little to nothing to do with "loss" and everything to do with application of force.

While your spring is absorbing , holding and then returning force, my steel pipe lever has put my wheel clearly in front of yours.

It not much more complcated then that.








<-------- might have been considered a sprinter back in the day.

He's not wrong there, can't argue with the spring energy equation .5 force times displacement. For the spring F=-kx since for work you integrate kx dx over the range of x you get the one half. e=.5k x^2 substitute kx=F to get E=.5Fx

bravissimo! nine pages...

http://gc3.smugmug.com/Other/Bikes/i...rjo0604h-M.jpg

OK, once again.

Your leg is not weightless. Some of the force you apply during the pedal stroke is used to lift your leg.

When you deform the frame at the BB, the BB doesn't just move laterally, it also tilts. The result is that at the maximum deformation point, the pedal is actually lower than if the pedal was at rest (and no forces acting on it, other than gravity) at the 6:00 position. So when the BB springs back, it is not just moving laterally, it is also tilting the entire crank assembly back up, which in turn lifts your leg.

The stored energy thus helps lift your leg. Thus, that's a small amount of energy that, instead of lifting your leg, goes to the drivetrain. The only way you lose energy is to the friction of the frame's motion.


I'm sure there is friction all over the place. But since a flexy frame doesn't get red hot after 20 minutes of vigorous cycling, it's unlikely that we are dealing with massive amounts of friction.

And yet again, to point back to the OP, the only way to confirm whether or not this is the case is via empirical tests. And yet, people continue to insist that they know the answer, despite the lack of evidence.

Seemed like a good idea at the time.

Okay, here is my question to the "don't look at force, look at energy" crowd:

Compare a push up to a plank. There is no displacement to a plank, does that mean the body uses no energy, compared to the displacement of a pushup?