For 1990-2009 cars

In manufacturing the brake rotor, tolerances of the braking surfaces for flatness, parallelism and lateral runout are closely maintained. The maintenance of close tolerances on the shape of the braking surfaces is necessary to prevent brake roughness or pulsation.

In addition to these tolerances, the surface finish must be maintained to a specified range, 60 Ra roughness or less. A new rotor falls into this surface finish range, as will a rotor that is refinished exactly as directed in Refinishing the Brake Rotors. The control of the braking surface finish is necessary to avoid problems of hard pedal apply, excessive brake fade, pulls and erratic performance. In addition, control of the surface finish can improve brake pad life.

Light scoring of the rotor surfaces not exceeding 1.5 mm (0.060 in) in depth is not detrimental to brake operation, and may result from normal use.