Planes and cars have problems braking if brakes are too hot. F1 teams complain also if brakes are too cold. What’s the reason behind so much variance?
Also, I have noticed, that basically any vehicle have smaller deceleration when moving fast than when moving slow. From elementary school physics – when I apply some force onto surface, I should get some amount of friction, so I don’t know why it changes. It this also related to the temperature, or is there unrelated mechanism behind it?
In: Physics
Brakes on a car is basically a clamp on a spinning metal disc. The clamp is operated with hydraulic force using the brake fluid. Most street cars use “organic” material to create friction when squeezed against the disc. Organic material is not tolerant of high temperatures. In some cases these materials melt and leave a “glaze” on the surface of the disc and the brake pad. The glaze is low friction and can cause a shudder under braking if not distributed evenly on the disc. Additionally some brake materials will off-gas under high heat and the gas can create a small buffer layer between the pad and the disc.
Better performing brake materials are semi-metallic or metallic and then into ceramic and other exotic materials. In addition to higher heat tolerance they are also less prone to the glazing problem.
The additional issue that arises is within the hydraulic system. As temperatures rise the brake fluid will boil and generate air bubbles. When hydraulic force is applied to “clamp” the brake disc, force will first compress these air bubbles and then close the clamp. This means for the same force applied you would allow the disc less with all other factors being equal. This problem is overcome by using brake fluid with higher boiling points (dot 3,4,5 ratings) and brake cooling ducts.
Latest Answers