Tom Adams wrote:
> Regarding the lighter wheel set being easier to accelerate, I once had
> an engineering professor explain to me that because every pedal stroke
> accelerates and decelerates, you continually reap the benefits of lighter
> wheels.
Well who am I to contradict an engineering professor, but I think he hasn't thought it through. I think it is the consensus of scientists who have studied bicycles that the slowing/speeding of the bike with each pedal stroke does not in itself require extra energy - except for the fact that wind drag is non-linear, (it's proportional to the square of the speed), so a more constant speed is slightly more efficient. That's because the reduced drag while you're going slower doesn't make up for the increased drag during the higher-speed periods. Heavier wheels result in a more steady speed, and thus should be ever-so-slightly MORE efficient than light ones, for steady speed, level riding. It's true, their extra weight will create a little more rolling resistance, so maybe it's a wash, but the people who actually calculate these things generally say the heavier wheel will be a little faster - the air drag difference will prevail.
Either way, we're talking infinitesimal amounts of difference. However it was enough that Francesco added lead weights to the rims of his disk wheels for one of his successful hour record attempts - specifically to reduce those changes in velocity from the variability of power output from the rider.
My point is not that heavy wheels are better, but that light wheels are ONLY an advantage when climbing or accelerating - and for climbing at a steady speed, they're no more important than weight elsewhere on the bike. ONLY when accelerating does the adage that "a gram on the wheel is worth two on the frame" hold true.
If you ask me for references, I'm afraid I wouldn't know where to send you except the Bicycle Science mailing list (formerly known as "Hardcore Bicycling Science") archives (http://search.bikelist.org/) - this subject has been thoroughly covered there, and I think the consensus was virtually unanimous on all the above. The only argument was about how important acceleration is to a bicyclist, with some folks holding the opinion that even for sprinters it's only marginally important - that even there, light wheels don't matter much.
I doubt that question will be really answered in our lifetimes. I did notice however that the top sprinters I made bikes for - Ken Carpenter, Paul Swift, Renee Duprel among others - used what seemed to me to be pretty heavy wheels. They wanted them very stiff and seemed willing - perhaps wrongly? - to give up some acceleration. I kinda stopped following track racing in the early-mid-90s when sprinters were starting to use disk wheels - are they still using 'em? But even when they were using spokes, they used lots of 'em, and not very light rims either.
I like the feel of light wheels, but I do believe many overstate the real benefits of them - beyond that snappy feel.
Mark Bulgier
Seattle, Wa USA