The Complete Guide to BMW M4 M Compound Brakes

With the new generation of the 2015 M4, an updated brake system was introduced to these models. The M compound brakes are very much different and special than the previous models.

According to Klaus Dullinger, M Engineer responsible for the development of the new BMW M4 brake systems:

M compound brakes have a grey-cast friction ring in a floating arrangement that is connected by pins to the aluminium brake cover. The pin assembly means that as the temperature increases, it is able to expand freely in a radial direction and subsequently cool down again without any residual deformation. This connecting system has been in used since the second generation of the BMW M4.

New Generation M Compound Brakes

bmwux guide m4 compound brakes

The new M compound brakes on the M4 have fixed-caliper brakes fitted to both the front and rear axles. The front axle will hold 4 pistons while the rear axle has 2 pistons. This is a big performance increase compared to the predecessor M4’s where the axles had heavy single-piston sliding calipers.

Running-In Period

On your first full tank of gas, you should restrain from using the maximum deceleration of the brakes and avoid hard emergency braking to allow your M compound brakes to have a “running-in” period. This is when your brake pads gets accustomed to the brake discs.

Bedding of the Brakes

bmwux guide m4 friction ring compound brakes

When you first take your new M4 off the lot, within the first 500 km (about 310 miles) of drive there is a process called bedding of the brakes linking to the friction ring. These 2 surfaces must become attuned with one another as the 20 µm (micrometer) thick cross hatch of the new brake discs needs to wear away. Once gone the bedding process of the new brake pad on the new disc can begin.

Crack Patterns across the Brake Discs

At times the surface of your M compound brake discs can show formation of crack patterns when the disc is exposed to cold weather and subjected to a heavy load. For example if you were driving in a race track and suddenly perform an emergency braking maneuver, the brake disc will become very hot in a short amount of time. The temperature can go from 20 degrees to 450 degrees. This is how the surface cracks will begin to form. Fortunately the cracks only show on the surface area.

Cool Down Lap

After driving on the race track with your new M4, it is important that the M compound brakes have time to cool down in an air stream. If you park your car right away while the discs are at 500 degrees, the heat the can be transferred throughout your brake system like the brake pads, back plate, damping plates, piston seals, and dust shields. All of these parts can be damaged by the heat. 

By performing a cool down lap, the air stream can bring the temperature of the brake discs down below 200 degrees.