Brake judder can be explained as a dynamical amplification of brake torque variation (BTV) when passing through a critical speed of a vehicle. The BTV arises owing to different geometrical defects e.g. disc thickness variation (DTV), disc runout and dynamical effects. DTV is usually the most important source of these fluctuations.
Measurements have been made on a passenger car with heavy DTV on one of its front brakes. The eigen frequency of the wheel suspension was found to be 14 Hz, corresponding to a first order critical speed of 95 km/h. These measurements qualitatively verify the brake model with a maximum caliper vibration amplitude close to 100 km/h followed by a slowly decreasing amplitude.