An updated brake system was introduced to the new generations of BMW M3s (2016 and later models). These brakes are very much different from the past models.
The new BMW M3 M Compound Brakes have fixed-caliper brakes fitted onto both the front and rear axles. The front axle holds four pistons while the rear axle has two pistons. The setup is a significant performance increase compared to the predecessor M3 where the axles had heavy single-piston sliding calipers.
According to Klaus Dullinger, the BMW M Engineer responsible for the development of the new standard BMW M brake system:
“M compound brakes have a grey-cast friction ring in a floating arrangement that is connected by pins to the aluminum brake cover. The pin assembly means that as the temperature increases, it can expand freely in a radial direction and subsequently cool down again without any residual deformation.”
On the first full tank of gas, drivers should restrain from using the maximum deceleration on the brakes and avoid hard emergency braking to allow the BMW M3 M Compound Brakes a “running-in” period. This is when the brake pads get accustomed to the brake discs.
Within the first 500 km (about 310 miles) drive of a new M3, there is a process called bedding of the brakes which links to the friction ring. These two surfaces must become attuned to one another, as the 20 µm (micrometer) thick crosshatch of the new brake disc needs to wear away. Once gone, the bedding process of the new brake pad on the new disc can begin.
At times, the surface of the BMW M3 M Compound Brake discs can show crack pattern formation. This happens when the disc is exposed to cold weather or is subjected to a heavy load.
For example, if you were driving on a race track and suddenly performed an emergency brake, the brake discs can become very hot in a short amount of time. The temperature can go from 20 degrees to 450 degrees in a few seconds. This is how the surface cracks begin to form. Fortunately, the cracks will only show on the surface area of the discs.
After driving the M3 around the race track, it is essential for the BMW M3 M Compound Brakes to cool down with air streams. If the car is parked while the discs are close to 500 degrees, heat can transfer throughout the brake systems and damage brake pads, back plate, damping plates, piston seals, and dust shields.
By performing a cool down lap, air can bring the temperature of the brake discs down below 200 degrees.