We've spent a lot of time trying to educate people about the pratfalls of using carbon clinchers in sutuations where they aren't the best tool for the job. Sometimes, when you're trying to make a point to a large audience, in trying to have the people in the metaphorical back of the room hear you, you wind up doing the metaphorical equivalent of shouting at the people in the front of the room. And we've come to realize that we've scared tar out of some of the people in the front of the room.
First, it's important to note that our carbon clinchers are a tested and proven product. They're EN tested, the manufacturer has a well established heat testing protocol that replicates braking situations, and beyond that they have been and are currently being used by several very well regarded brands. These are not rims without a pedigree, nor are they just some ones we happened to find on eBay. They're good rims. I'm not a tracking junkie, but my set of 38s has I don't even know how many thousands of miles on them, have been up and down some horrible number of thousands of feet of climbing and descending, have been raced on dirt roads, been used as commuter wheels, raced the 2011 Killington Stage Race (under my wife) and many other races, and show no sign of let up. When you start a wheel company, the delusion is that you're going to be the Imelda Marcos of wheels. The truth is a little different, so as has been the case for a while, RFSC38s are the ONLY wheels I currently have.
So if I've done all of this going downhill on my wheels, how is it that I'm here writing this instead of showing off my shiny toe tag at the local morgue? For one, I avoid going down huge hills with a few thousand of my closest friends. A mountain descent that I wouldn't even think twice about would give me waking nightmares if I had to go down it with a few thousand of my closest friends.
(what happens if you're last up the hill?)
Glazed brake pads and tubes popped by hot rims have actually been around far longer than carbon clinchers have been on the market, it's just that carbon leaves less room for error in dealing with brake heat. So with that in mind, let's look at some techniques and skills that will DRAMATICALLY reduce the chance that this issue will ever affect you.
#1 Go fast. I laugh every time I hear someone credential the wheels he's bought by saying "I went 45 down a big hill no problem!" That's the easy part - go 15 down the same hill and get back to me. Going fast means that you aren't locked on your brakes, and that there's lots of air passing by to cool everything down. I'd gladly go down the Tourmalet with carbon clinchers if the road was closed, because I'd go HELLA fast. With the group pictured above? I wouldn't be as comfortable going down Old Angler's Hill (our local HO-scale Tourmalet) on ANY wheels in that mob scene.
#2 Brake hard! When you use your brakes, USE them. Don't drag on them endlessly, letting heat build and build and build. When you need to slow down, slow down. When you don't, don't. Be aware that when you decelerate quickly, your body will want to keep going, so move your weight back and use your arms to gently resist getting thrown forward.
#3 Brake BEFORE the turn. In cyclocross you say "it's not how fast you go into the turn but how fast you come out of it." Slowing to a speed that you know you can hold through the turn will keep you off the brakes during the turn. Your tires can either brake OR turn - they can't do both at the same time. Go into the turn at the right speed and you'll come out better every time.
#4 The front does the work. On a road bike, a HUGE percent of the braking force comes from the front brake. Use the front brake. The rear does a little, the front does a lot.
#5 Feather. When our rims are tested, the brakes are alternated off and on in even cycles. The cooling that happens in the "off" periods is astonishing - the rims can lose 80* in 5 seconds. So getting off of your brakes for just a few seconds causes the thermometer to go down instead of continually rise. Again, just clamping on your brakes is always the wrong technique. Use your front to slow yourself for a few seconds, then use the rear, then back to the front.
#6 Brake earlier and more in wet weather. Wet rims take longer to brake, and they also take longer to heat up. Use your brakes a bit more in wet weather, and leave yourself plenty of room to stop.
#7 Maintain your pads. When your pads get hot, the suface gets "glazed." This is like a thin hard layer on your brake pads that causes uneven, grabby, ineffective braking. After a ride in which you've used your brakes quite a bit, scuff the surface of the pads with an emery cloth or 120 grit sandpaper. Replace your pads when they get worn thin. Ask us for new ones. Just not every week.
#8 Be light. Sorry to be the bearer of bad news but brakes transfer kinetic energy into heat through friction. The heavier the rider, the more kinetic energy there is to be converted into heat, ergo more heat. At 165, I will have less of an issue than a 200 pound guy, and my wife whe doesn't weigh very much at all will have fewer problems than either of us.
#9 Mind your tire pressure. We mandate a maximum tire pressure of 120 psi because, as we all should have learned in school, heat expands air. If you start with your tires pumped up rock hard, when they heat up (which they will through the heat of the day and road friction as well as through using your brakes), they will exert huge pressure against the brake track. More moderate tire pressures don't put such high pressures against the brake track.
The simple fact is that most people, most of the time, will have zero problems at all from heat with carbon clinchers. Exercising good techniques will increase the range of safe operation by quite a bit.