BRAKES ARE CRITICAL FOR YOUR SAFETY!
Brake components need to be inspected regularly and replaced as necessary.
Street and Highway Use
Brake pads should typically be replaced when approximately 1/8" to 3/16" of friction material remains on the steel backing plate.
Brake rotors should be replaced before their thickness has reached the prescribed "Worn Rotor Minimum Thickness" limit (expressed in millimeters) engraved on the edge of the brake disc.
MINI does not recommend 'turning' used rotors for re-use. New brake rotors should be installed when replacing brake pads.
Track and Competition Use
Due to the extremes of heat and pressure encountered by brake systems used for track and competition applications, all brake system components (pads, rotors, calipers, lines, hardware and fluid) must be compatible and should be inspected between sessions. Brake pads and rotors should be replaced before they reach the wear limits described above.
Just a FYI:
BMW suggests: Servicing and Upgrading Brake Components should only be performed by a competent and qualified auto mechanic. Any incorrect installation may cause serious safety problem or an accident. If you are not a competent and qualified mechanic, you should not attempt to service your brakes. Take your vehicle to the dealer or competent and qualifed mechanic for servicing.