The thermal losses from a flexy bike frame are probably completely insignificant. The downtube of my bike rarely gets too hot to touch. The problem with flex is how it interfers with power transfer to the road. The work done in displacing / flexing a frame is mostly returned as the material flexes back to a neutral position, but what about the timing of all this? If the frame "gives way" when you are applying maximum force to the pedal (the downward portion of the pedal stroke) will is really flex back in such a way that it contributes to energy input later in the stroke? Or will it simply move back, without detracting further or contributing... or will it actually further detract from the transfer of power to the road? I know one big rider (6'3") who has ridden a lot of frames, the stiffest of which are modern OS alum. bikes that he really feels are a benefit to guys his height. The only frame he ever really complained about as being "flexy" was bonded Ti in conventional "steel" diameters. Bad design. In any case, he never complained that it "sucked up" his energy, but rather that it flexed so severly that he couldn't apply full power without the thing getting all twisty. I guess my point is that one problem with sever frame flex is that it confounds the act of pedalling, even if the theoretical hysterisis losses are minimal. Bikerdaver@aol.com wrote: Mike- From pretty much the explainations from frame builders like Richard Sachs, comments from Steven Thomas and Brandon Monkeyman and general armchair phyics, you will find that the comments you hold dear and true, are pretty much wishfull thinking. Its been a while since my college physics course as well, but the comment by Phil brown pretty much dials it in for us, "One word: entropy. You never get out of a system what you put in." Check it out in a dictionary or physics text, you'll see what they mean about this flex issue. Cheers, Dave--haven't been on an English Racer for years--Anderson Cut Bank MT
In a message dated 6/2/2002 7:51:54 AM PDT, bikevint@tiac.net writes:
> Acutally this analysis is not correct - when the frame springs back all the
> energy that went to move the frame one way moves it back the other - and
> that movement is augmenting the pedal stroke - energy can't be wasted - it
> has to be conserved (i.e go somewhere and steel just doesn't dissapate a
> quanifiable amount of energy as heat from what I understand). Again, we do
> "waste energy" from extra body movement, but a frame cannot absorb energy
> in any relevent extent.
>
> Many of the best riding quickest feeling bikes are very flexible - again,
> it is having the right flex that is important.
> Mike Kone in Boulder CO
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