Originally Posted by
WeLuv2Bike
Hi Jan, How much heat build-up occurs in descending, say a 7% LONG grade, like Hurricane Ridge, on a single bike? My concern is having a tire blow-up.
As FBinNY says, there are too many variables to say precisely but we can make some estimates. Based on acidfast7's video, the temperature increase is about 80°C. Based on
Gay-Lussac's law and assuming a 100psi starting pressure, the increase in pressure for that kind of temperature increase is about 25psi. In other words, the pressure goes from 100 to 125psi. Is that enough to blow off the tire? Maybe but maybe not. It would depend on too many factors.
Something to consider in acidfast7's video link is that the rim is a carbon rim. Carbon doesn't dissipate heat as quickly...or, perhaps, at all...as aluminum. The heat build up from braking an aluminum rim would be lower and it would cool more quickly. That will result in a smaller pressure increase.
Originally Posted by
WeLuv2Bike
To minimize heat building up in the rims: Is it better to break intermittently hard and release versus applying a lighter constant pressure? Thank you!
Look at the video again. About 3 seconds after the squeal starts...who could stand that for more than a couple of seconds
...the temperature jumps up to about 80°C. That would be an increase in pressure to 113psi. After 15 to 20 seconds, the temperature is 100°C which gives a pressure of 120psi. It takes 30 or 40 seconds of braking to get to 120°C.
Constant braking is not your friend. Punch the brakes hard, scrub speed, release the brakes, repeat as needed.