Brake rotors are large diameter discs attached to the axle of vehicles. These are clamped between brake pads to stop them, and the axles and wheels from rotating. This system is called disc brakes. Disc brakes are very effective and can be counted on with only regular maintenance to provide faithful service for your vehicle. The pads that are squeezed to the disc are made out of special high friction materials, which are designed to be worn away rather than wear away the surface(s) of the discs. The repeated use of the brakes or continuous use of the brakes can often cause heat to build up in the disc.

In applications, such as high speed use or heavy load use, the brake rotors are often constructed of more than one plate and are also often either drilled or slotted to allow airflow on the surfaces of the rotor. This airflow allows the disc to operate at a lower temperature by dissipating heat through the air holes and the greater surface area of the disc, (when considering the profile(s)of the slots or holes.

Keeping the temperature of the disc low is critical for (at least) two reasons. The first is that hotter discs will adversely affect pad life. The pads are designed to operate within specified temperatures, and higher temperatures will cause the pads to slough material faster than normal. If your brakes run too hot, your brake pads will wear out more rapidly. The second problem that can arise when you overheat your brakes is that there is a chance that you can warp the discs, (rotors), from the excessive heat.

Brake rotors get chewed up by the action of the brake pads, even when they are being used properly and maintained properly. As the brake rotors get gouged, the valleys aren't in contact with the brake pads. This decreases even application of friction and increases the heat generated from the friction, by localizing friction only to the peaks of the grooves gouged into the rotors. As you can see this will increase the wear on the rotors, and the pads.

Brake rotors are designed to be resurfaced when this happens. Each resurfacing removes more material from the rotor plate, and makes the rotor less stable under heat and pressure stress. The Department of Transportation has specific requirements as to how thin a rotor can get before it is no longer deemed serviceable.