There's two types of failures due to overheating:
-blowout of tire (and with that, often the sidewall)
-delamination of sidewall, which can create a 'blowout' since the tire can't hook onto a failed wall.
Blowout of tire occurs when the heat is too high, raising the pressure inside the tube, and hence a blowout - which can often damage the sidewall of the rim because pressures were exceeded. Then people instantly point to the failed rim sidewall and think "it couldn't take the heat from braking"... which isn't an entirely accurate statement. Latex doesn't take heat very well, so the temperature of the air inside the tube increases dramatically which results in too much pressure on the sidewall, and hence the blowout of both tube and rim. This will happen with both aluminum and carbon rims, but more likely with carbon as it tends to 'warm up' faster than aluminum and transfer heat rather quickly to the tube. Aluminum rims are more likely to withstand the pressure of the increased pressure, so the sidewalls of the rim are less likely to fail. Well built carbon clinchers with well designed braking surfaces not only offer better heat retention, they also offer better friction against the pads - and therefore better braking. ZIPP is a great example of this, as well as Xentis. The open mold rims though aren't as far away as one might initially think: they're remarkably decent, if not great for most confident and experienced riders.
Delamination happens when the rim is not built properly and often with poor choice of resin used in the braking surface area. It's exactly what it sounds like: the layers of laminated carbon come apart when the resin wears away/melts. The sidewall then fails because it is weakened, and the pressure of the tube which normally pushes the tire into shape and helps keep the bead hooked into the wall then come loose and you get the blowout effect. It happens rather quickly and often the tube itself will pop when in contact with the surface of the road or other, so then you get a blowout...
Before anyone goes all gonzo and screams "thems chinese open mold rims are cheap!" keep in mind delamination has been documented on Lightweights, too, and all braking surfaces - aluminum or carbon - will wear away over extensive use. An aluminum rim which has a worn down braking surface will have less grip on the pads but also allow heat to transfer to the tube (the wall is thinner), which will result in a blowout.
So in summary, two types of failures are possible that both may result in blowouts:
1. Sidewall is fine but transfers too much heat -> tube can't resist heat, increases air pressure -> tire blowouts out and often sidewall is impacted from too much pressure, also failing.
2. Sidewall can't take the heat -> delamination -> tube/tire are no longer held in place -> blowout.
Butyl tubes offer greater heat resistance. But even with the fancy wheels of ZIPP and Xentis and their high-end braking surfaces: they state NOT to use latex tubes. Subtle hint at one of the sources of all the hub-bub in the past.
. Admin feel free to delete thread.
