Info - Visual Brake Rotor Surface Cracking

Important: DO NOT replace OR resurface rotors for small surface cracks that are described below.

The pass criteria for thermal fatigue testing specifies that the rotor is allowed to have small thermal cracking up to 2/3 of the brake plate surface. The brake plate surface for the front rotor is 50 mm (1.96 in) radially which means cracks are permitted up to 33 mm (1.29 in) radially across the rotor brake face in length. This would be the pass criteria for the end of severe testing. To have a large safety margin, a rule of thumb -- "small" thermal cracks are allowable and the rotor does not need to be replaced unless the cracks connect from hole to hole or the crack reaches the OD of the rotor.