BMW is renowned for soft brake rotors, they give much better stopping performance, but tend to wear out fairly quickly. Despite this, it is not always necessary to replace the rotors with every brake pad change - if the rotors are within tolerance.

The major reason for replacing rotors is due to excessive lip on the outer circumference of the contact area. A large lip will cause the pads to sit on an angle, reducing contact between pad and rotor to less than half of the pads width. This results in very low pedals, and diminished braking capacity.