The Z4 M Coupe comes with E46 M3 Competition Package (CP) brakes as standard, which perform better than most BMW stock brakes under track conditions. Heat build-up and eventual fade can be managed with braking techniques and quality after-market pads, but there's no getting away from the mushy, uncommunicative pedal feel at the limit, caused by its sliding calipers.
It was necessary, and more in keeping with its racy nature, that the M Coupe be fitted with aftermarket fixed-caliper brakes. This project, with its quantitative back-up, came about from driving a friend's E46 M3 CP, both before and after a Brembo fixed-caliper upgrade. At the track, the seat-of-the-pants change in pedal feel, effectiveness and consistency was readily apparent. As a scientist, I felt compelled to measure this difference and back it up with real numbers.
For any big brake upgrade, the main considerations are: what is available? And how much wheel clearance is there? Fortunately, Brembo launched its big brake upgrade kit for the Z4M earlier this year. I decided to stick with 18-inch wheels, due to the anticipated amount of track time, so clearance was an important issue. When the custom forged ZX3-R wheels were still at the planning stage, Forgeline contacted Brembo to ensure that the new brakes would fit behind them properly. After an exchange of CAD files, the correct offset was chosen for front caliper clearance.
Knowing there needed to be some custom trimming of the inner rotor mudguards to accommodate the larger fixed calipers, I decided to have the four-wheel upgrade installed professionally. Tunerworks Performance in Calgary did the work, along with a full brake fluid flush and system bleed. Each Brembo GT big brake kit has a pair of four-piston fixed calipers, Brembo HP1000 performance brake pads, vented and slotted two-piece floating rotors (14x1.3 inches up front and 13.6x1.1 inches in the rear) and includes all necessary adapter brackets and hardware, as well as stainless steel flex lines. The HP1000 brake pads are designed with improved control, friction levels and resistance to fade, and have a longer life when compared with OEM pads.
Each front set-up saved 3.5 pounds of unsprung weight, even though the OEM front rotor size is much smaller (13.5x1.1 inches). Because of the increase in rotor size from 12.8x0.8 inches, there was no net weight change in the rear. Note that the weight is saved or balanced with the Brembos, despite the increase in rotor size, by using aluminum hats and calipers instead of heavy cast iron (as with the OEM parts).