Brake energy and wear calculator
Every stop turns the whole kinetic energy of the car into heat in the discs. It is a startling amount of energy.
mm per 1000 km
%
Energy in one stop
8000.0kJ
- Taken by the front brakes
- 5 600 000 J
- Rough disc temperature rise Assuming two 8 kg iron discs and no cooling.
- 761 K
- Pad life
- 66 667
- Braking energy per 1000 km
- 3200.0 MJ
- Litres of water that would heat from 20 to 100 C
- 23.90
Show the working
- Vehicle mass = 1600
- Speed before braking = 100
- Hard stops per 1000 km = 400
- Usable pad thickness = 10
- Wear rate = 0.15
- Share taken by the front brakes = 70
- v = 100 = 100
- energy = 1600 * 100^2 / 2 = 8 000 000
- Energy in one stop = 8 000 000 / 1000 = 8000
- Taken by the front brakes = 8 000 000 * 70/100 = 5 600 000
- Rough disc temperature rise = 5 600 000 / (2 * 8 * 460) = 760.87
- Pad life = 0.15 > 0 ? 10 / 0.15 * 1000 : 0 = 66 666.7
- Braking energy per 1000 km = 8 000 000 * 400 / 1e6 = 3200
- Litres of water that would heat from 20 to 100 C = 8 000 000 / (4184 * 80) = 23.9006
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- kinetic energy = (1/2) m v^2
- temperature rise = energy / (mass x specific heat)
A single stop from 100 km/h in a 1600 kg car releases about 617 kJ — enough to boil nearly two litres of water.
Brake fade is this energy arriving faster than the discs can shed it. Repeated stops without cooling are what causes it.