What's the difference between the stock rotors and the same rotors from an aftermarket?
Well, aside from the warranty, which is REALLY important to me, the stock rotors are spin-balanced at BMW after the OEM manufacturer (Brembo, Ate, Balo, etc.) ships them to BMW. Some manufacturers claim to spin balance their rotors, but they may use less reliable clip-on or glue-on weights, whereas BMW shaves metal off the rotor to achieve the proper balance. My experience is that from a reputable BMW dealer with an aggressive parts department, you can buy rotors CHEAPER from the factory. The aftermarket dealers that advertise in Roundel have been, in EVERY case, MORE expensive (to my surprise as well), and there is rarely a warranty with their products.
My Jet Black's
'03 3.0i Z4 Loaded
'02 325Ci Loaded
'06 330xi Loaded