Brake fade
In any vehicle, such as an automobile or motorcycle, that utilizes a friction braking system, fade, or brake fade is the reduction in stopping power (i.e. the reduction of friction between the brake pad and the brake rotor or drum) caused by a buildup of heat in the braking surfaces (and in the case of drum brakes the change in dimension of components in response to heat; the curvature of the brake shoes then failing to match the curvature of the brake drum). This reduction of friction can be caused by the gasification of organic materials in the brake pad causing a gas cushion to form between the pad and disk, or by the melting of the binding resins in the pad that then act as a lubricant. The former is most common on new pads and is termed "green fade"; brake manufacturers typically bake new brake linings to minimize green fade. In both of these forms of fade, the brake pedal feels firm but there is reduced stopping ability. Fade can also be caused by the brake fluid boiling, with attendant release of compressible gases. In this type of fade, the brake pedal feels "spongy". This condition is worsened when there are contaminants in the fluid, such as water, which most types of brake fluids are prone to absorbing to varying degrees. For this reason brake fluid replacement is standard maintenance.
Brake fade occurs most often during high performance driving or when going down a long, steep hill. Owing to their configuration this is more prevalent in drum brakes. Disk brakes are much more resistant to brake fade and have come to be a standard feature in front brakes for most vehicles, although the brake rotors can become warped due to excessive heating.
Brake fade and rotor warping can be reduced through proper braking technique; When running down a long downgrade that would require braking simply select a lower gear (for automatic transmissions this may necessitate a brief application of the throttle after selecting the gear). Also, periodic, rather than continuous application of the brakes will allow them to cool between applications. Continuous light application of the brakes can be particularly destructive in both wear and adding heat to the brake system. Finally, new brakes should used as gently as possible for the first 100 miles or so to "break them in" and eliminate green fade.
High performance brake components provide enhanced stopping power by improving friction while reducing brake fade. Improved friction is provided by lining materials that have a higher coefficient of friction than stock brake pads while brake fade is reduced through the use of more expensive binding resins with a higher melting point along with slotted, drilled, or dimpled rotors that reduce the gaseous boundary layer in addition to providing enhanced heat dissipation. Heat buildup in brakes can be further addressed by body modifications that direct cold air to the brakes.
References and sources
Times Online article accessed 2006-10-23
Tire Rack article accessed 2006-10-23