Hot Rim Tire Blow-Off

Bicycle riders using clincher tires have noted for years that under hard braking the tire will sometimes unseat or "blow off", causing the tube to rupture, deflate with a bang, and often causing a crash.

The root cause of the blow-off is not understood. Theories include: the tire pressure goes too high and the clinch can no longer retain the high pressure; and the hot rubber becomes too slippery to retain the bead and "creeps" under load.

Jobst Brandt, Peter Hartwell, and Bob Walmsley instrumented a wheel with a pressure and temperature sensors, then did a series of braking trials to measure rim temperature and tire pressure.

The rim temperature went from 20°C to 100+°C, but pressure increased only slightly. For example, in 5 minutes spent over 80°C the tire pressure went from 590 kPa (5.9 bar) to 620 kPa (6.2 bar) or about 5%.

This suggests tire pressure is not a significant factor in blow-offs, and bead temperature is the major effect leading to blow-off.


Click the image for a larger version.

Note that the pressure reading is very "jumpy" during braking. This is probably due to vibration of the pressure sensor during braking.

The sharp "dip" in pressure in the middle is when the pressure monitor was removed to inflate the tire.

Raw data here: biketest1c2.xls. Aside from the effects of vibration, the pressure readings have a resolution of roughly 5 kPa (0.05 bar) and the temperature sensor a resolution of roughly 0.1°C.