Disc thickness variation (DTV) is the main cause of brake judder. Cold judder can be caused by a number of mechanisms. Uneven wear leads to disc thickness variation as the wheel rotates. The thickness variation leads again to torque variation that is sensed as vibrations by the driver. Hot judder occurs due to heavy usage of the brake that results in uneven heating or hot spots that cause the distortion of the rotor of a disc brake, which also causes brake torque variations.

This paper presents a practical way of measuring operational in-service DTV at constant speed and during braking application, and how this information, together with its corresponding DTV orders, can be correlated with the real vehicle body deformation (bending & torsion) due to realistic brake torque fluctuations.

García J.J, Ferrer B, Squadrani F, Mateu, R, Applus+IDIADA, Santa Oliva, Tarragona, Spain