Originally Posted by
Fredo76
I believe my signature is a concise statement of the physics, and not an exaggeration. At least, nobody answered my points last time around - they were too busy congratulating themselves in the 'how to learn' thread, iirc. If you know the correct coefficient for the simplifying assumption that the rotating weight is all at the radius, do tell..
It might be that we agree more than disagree and it's just some word choice that separates us.
Would you agree that weight at the rims or tires
only matters 2x as much as weight on the frame and elsewhere
when accelerating? If you agree with that, then we're on the same page. If you disagree, then I think you have diverged from the thinking of every scientist I've ever heard on the subject.
When climbing at a steady rate, rotating weight does matter, but only the same amount as frame etc. Both matter equally, an ounce = an ounce.
When riding at a steady rate on the flat (as with the hour record on the track), neither rotating weight nor frame etc weight matter except for the tiny influence they have on rolling resistance. But the whole range of wheel weights from lightest to heaviest is not enough to affect the RR to a degree worth worrying about, even for racers. Thus Moser's extra-heavy wheels when he broke the hour record.
So, an ounce on the rims or tires truly is worth two on the rest of the bike,
with respect to acceleration (only).
Since we humans are capable of only weak acceleration, especially at racing speeds (like the sprint at the end of a road race), this effect gets swamped by more powerful factors like aero drag. And the time we spend accelerating, as a fraction of time spent on the bike, is minuscule. So overall, slower accel due to rim weight is lost in the noise, unimportant for most riding.
About the only common scenario where it matters enough for me to care about is "spirited" stop-and-go city riding, where you're repeatedly sprinting away from stop signs and traffic lights.
Light wheels do
feel snappy, and I like that feeling, and that's enough reason for a lot of us to prefer light wheels. But they won't shave much time if any from your time on a century, brevet or time trial. Or, I should say, not more than saving that same weight elsewhere on the bike, which matters if it's hilly.
I haven't taken part in this dicussion here (BF) before but I get the feeling it's been hashed and rehashed, so maybe I should shut up now. Not trying to have the last word, please go ahead and tell me where I went wrong.
Mark B