Brake Disc is a component of the braking system on a vehicle that slows the wheel by mechanical, hydraulic, pneumatic or electromagnetic means. The brake disc is connected to the wheel rim and is a part of the braking system on most cars and light trucks.
During braking, the kinetic energy of the vehicle is converted into thermal energy via friction between the brake pads and the brake disc. This is done to generate a braking force that is transmitted from the caliper, through the brake hose and into the wheel hub. This force is then transmitted to the wheel rim, causing the driver to stop.
The temperature of the rotor surface changes as the brake is applied and the coefficient of friction (m) varies with this change. Friction materials can vary +-10% from their nominal values.
This variation is often mistaken for a "warped" brake disc; however, warping refers to the disc's surface deforming due to heat. A more common cause of disc thickness variation is uneven pad material transfer.
Uneven pad material transfer occurs when the braking pads are not broken-in properly or are improperly selected for the given brake application. In a properly broken-in system, the disc and pads are heavily applied multiple times in succession to create a smooth interface between them.
The most important factor in preventing uneven pad material transfer is the proper selection of brake pads. When a brake pad is chosen for the application, the selection should be made in accordance with the optimum temperatures that it will operate at. This selection is often done by analyzing the brake system at different times of the year, as well as the climate and weather conditions. The brake pads should also be changed as soon as they are no longer performing satisfactorily.