Stevan Thomas wrote:
> Energy spent bending the frame is energy not spent making the
> wheels go around. When the frame springs back, none of that
> energy goes into making the wheels go around either.
Stevan, do you know this is a controversial statement? Some scientists that have thought about this question think *most* of the spring energy goes into making the wheels go around.
Everyone agrees some is wasted, turned into heat, a process called hysteresis. The question is how much. The answer may never be known, as bicycle science hasn't answered it with any precision in the hundred + years people have been asking the question.
The mechanism for the return of the spring energy as useful work is not a mystery though, and I think it's probably provable that *some* of the spring energy is returned usefully, though I can't prove it myself (don't have a physics lab or know how to use one!)
But I'm in the camp that thinks most of the spring energy is useful, partly from looking at all the great riders who have chosen the most flexible frames they could find. Example: Sean Kelly on Vitus aluminum. His average output was what, half again more? - than that of anyone on this list, and his peak output in a sprint, maybe double. How many Tour green jerseys did he win, 5 maybe? Mostly on those Al noodles. Of course he might have won even more editions of Paris-Nice if he hadn't been wasting so much energy, but it's hard to imagine these pros wouldn't notice that they were faster on stiffer bikes, if indeed they were.
The best you can say for the stiffer bikes is that if they are more efficient, it's by too small an amount for the pro peloton to notice. Note, some pros will *say* they like a stiff frame, then go and choose a flexible one without realizing it is so. Many times I've heard a racer say he likes a particular frame because it's so stiff, when I knew it was one of the more flexy ones out there. He liked it, and thought he liked 'em stiff (had been told stiff was good), so the one he liked must therefore be stiff, right?!
Greg Lemond for instance was known to win on some amazingly flexible frames, then wrote in his book that the most important thing about a race frame is that it be stiff! How would he know? He'd probably never even ridden a really stiff bike - he'd been given a succession of light race bikes throughout his career and probably never threw his leg over an SP frame let alone a Cannondale. In fairness to Greg, his book was probably ghost-written.
Then there's the theory that the "right" amount of springiness suits the human engine in a way that makes some flex better than none - thus a hypothetical infinitely stiff frame would be slower.
Example: Davis Phinney one season had two supposedly identical Serottas made of True Temper tubing, and raced them both enough to notice that he consistently liked one better than the other. He couldn't put his finger on it, one just felt faster to him, and he wondered why. So at the end of the season he gave the two frames to True Temper and asked them to test them and tell him the difference. The lab boys found that the one Davis liked was significantly more flexible, and that that was the only significant difference they could find.
I know none of this proves anything - I just wanted to make sure everyone knows that the jury is NOT in on this one - the "stiffer is more efficient" camp has not proven their hypothesis either. I doubt it'll ever be settled.
Hope this isn't too off-topic or too boring, let me know if it is.
Mark Bulgier
Seattle, Wa
USA