New drilled and slotted rotors...
New drilled and slotted rotors from BMW Performance
In terms of bragging rights, few cars can compete with the 135i's stock Brembo-derived six-piston calipers and 13.3" (338mm) rotors, which leave cars like the M5, M3 and 335i looking under-equipped.
Thanks to the catalog of parts available through BMW Performance, owners of the base model 128i can also enjoy these brakes with a $2425 upgrade from your dealer. The kit includes funky yellow calipers and drilled/slotted rotors.
While we obviously didn't need to spend that kind of cash on the painted calipers, the rotors intrigued us. There are all kinds of theories about cross-drilling and grooved surfaces including better pad bite, release of heat and gases, etc. More than that, they look good, so we thought we'd try them!
Again, BMS took this in its stride, removing the two 10mm allen bolts that secure the caliper to its carrier. With the caliper supported, remove the 6mm allen screw from the stock rotor and replace with the new part. When refitting the caliper, use blue Loctite on the bolts and torque to factory specs. Don't use power tools because the aluminum caliper is "relatively soft".
In use, there is a marginal improvement in braking, particularly during repeated hard use. However, the trade-off is slightly more noise when the brakes are applied. You soon ignore it, though.
 6mm allen screw secures rotor...  6mm allen screw secures rotor to hub |  Two 10mm allen bolts secure...  Two 10mm allen bolts secure caliper to carrier. Use blue Loctite when replacing, and don't over-tighten. Bed-in new rotors as specified |  For factory parts, these brakes...  For factory parts, these brakes certainly look good and perform well |