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.

متوسط

About 2 hours

التعليمات

Energy per stop and clamping force

جارٍ تحميل دفتر Jupyter…

Measure a disc after braking

On a bicycle with disc brakes (or a car, with its owner's help and on private ground), measure the disc temperature with the infrared thermometer before a stop, then brake firmly from a steady speed to a halt and measure again straight away — on the braking surface, not the shiny spokes. Repeat three stops in quick succession and watch the temperature climb: each stop adds heat faster than the disc can lose it. Wait five minutes and measure again: most of the heat has gone. That cooling rate is what a ventilated disc improves. Do not touch a disc after braking; it can be well over 100 °C. Look at the pads through the calliper: glazed, shiny pads have been overheated.

الأدوات المطلوبة:

ميزان حرارة بالأشعة تحت الحمراء

ساعة إيقاف

قفّازات عمل جلدية

History and context

**Frederick William Lanchester, Birmingham, 1902** — a calliper disc brake on a motor car. No patent number is asserted here. Disc brakes spread in aircraft in the 1930s and 40s; in cars they came back in the 1950s, when Jaguar raced with them at Le Mans in 1953, and from the 1960s they became standard at the front. **Honest limits.** No self-servo, so a disc needs more clamping force than a drum — hence the servo assistance on most cars. Exposed discs collect water and dirt. And a disc can only absorb so much before its pads fade too: sustained descents still call for engine braking.