Join Date: May 2002
Location: Near Portland, OR
Bikes: Three road bikes. Two track bikes.
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From what I understand, on an aluminum wheel (not CF with aluminum braking surface), heat is dissipated into the rim which acts as a big heatsink. In a CF rim (and, notably, CF rims with Al braking surfaces, which is why the Al surface sometimes comes unlaminated), the polymer in the rim doesn't dissipate heat all that well, so most of the heat is dissipated into the brake pads. When CF wheels first came out, people were using cork, which simply had less stopping power so less total heat was dissipated. Now, I think the brake pad material is more heat conducting and more thermally stable so you can keep your braking power and brake longer and harder without the brakepads melting or glazing or whatever they do when they overheat.
This is from my background in thermal management as a mechanical engineer and what I've learned by poking around this subject, not any experience with CF wheels. CF wheels only really work, I think, because brakes aren't used all that much in road biking and especially racing. Most of the time it's either hard braking for very short durations (corners and such), or feathering, both of which don't involve much total thermal energy.
Cat 2 Track, Cat 3 Road.
"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --the tiniest sprinter