When setting an M3 or M4 for high performance driving, properly setting the rear camber and toe will yield significant results. The rigidly mounted rear subframe and relatively low count of rubber bushings in the back of the car means that alignment changes translate very directly into the car’s behavior, and can be felt immediately when a change is made. The factory eccentric suspension bolts have a reasonable amount of adjustment range for a variety of ride heights and possible alignment settings, but are not a perfect solution.
The rigid camber shims will allow a technician to precisely set camber by choosing one of 5 shim offsets to install in the rear suspension. The shims can be used in either the normal orientation, or flipped, resulting in 9 different positions, divided into 1mm increments. This will give an exact camber setting, and ensures absolutely no change in alignment even in the harshest driving conditions.