The Disc Brake: A Stop Is Heat, and the Disc Can Get Rid of It

Frederick Lanchester, in Birmingham in 1902, fitted a car with a brake that clamped a disc between two pads, like a bicycle's calliper brake closing on a flat plate instead of a rim. The idea came back strongly in the 1950s, when faster cars were fading their drum brakes on long descents. A brake turns the car's energy of motion into heat, and in a hard stop that heat has nowhere to go but into the brake itself. A disc's friction faces are open to the air, and a ventilated disc pumps air through its middle as it turns; there is no self-servo, so the braking stays steady as the pads heat. This rung works out how hot a disc gets per stop and how hard the calliper must clamp, and measures a real disc's temperature after braking.