Project E39 M5: StopTech Front & Rear Trophy Kit Installation

by Martin Gonzales

In our Brake Refresh Article we maximized the capabilities of our E39 M5’s OE braking system by using StopTech’s Sport Axle Pack, which includes slotted rotors, stainless steel braided brake lines and Sport (formerly Street Performance) brake pads. Front brake ducting was also added in order to improve on our project’s susceptibility to brake fade. Though these improvements left us with a braking system that performed better than stock, the E39 M5’s stock system has a lot of room for improvement.

It is puzzling why the M cars of the E39’s era stubbornly stuck to using cheaper production single piston floating calipers. Exceptionally puzzling for the E39 M5 considering one of its main rivals, the S55 AMG, came equipped with 4-piston race inspired fixed calipers. Let’s also not forget the M5’s properly sized, but extremely overweight front rotors. The front one piece full steel rotors weigh almost 27 pounds each! That is a lot of un-sprung weight we could potentially save.

Many of our project cars are equipped with race level big brake kits that come with fixed multi-piston calipers, larger and better ventilated rotors, and their components are usually much lighter than their stock counterparts. The improved performance and weight savings we’ve achieved with our choice of brake components in the past is exactly what we want for our M5. We will look to achieve our goals by using a modern state of the art braking system from the brake experts at StopTech – the highly coveted Trophy Kit.

The StopTech front and rear Trophy kits come with with everything you will need to upgrade your M5’s brake system. For reference, the part numbers for our front and rear kits are 83.135.6700.R1 and 83.135.0047.R1. The R denotes the Trophy race caliper.

For the front brakes, we opted for StopTech’s Trophy six-piston ST60 caliper equipped system. The Trophy kits differ from the standard StopTech systems in more than just their finish. The calipers are CNC machined down to reduce weight after careful FEA analysis so weight is removed without sacrificing the stiffness of the calipers. Generally, this saves about a half pound from each caliper. Trophy kit calipers are also not powder coated, but rather hard anodized. Unlike powder coat, hard anodizing will not deteriorate or burn off with heat. It is also a very hard, corrosion resistant and durable surface finish and to scratch it, you actually have to damage the base metal.

StopTech also has a 4-piston caliper upgrade kit for the E39 M5 in case your wheels specs limit you to a smaller front caliper. We chose the 6-piston caliper for its much larger brake pad area. The M5 is a heavy 4,000 pound car so it needs all the brake you can put under it!

The ST60 caliper is very stiff, the black bridge is an aid to assure a stiff brake pedal and helps braking efficiency by assuring all the hydraulic force is transferred to the brake pads. A stiff caliper helps assure a consistent brake pedal and even pad wear.

Part of the ST60’s stiffness is attributable to the CNC machined bridge that spans the open area of the caliper and is bolted to the caliper body in 4 places. This is a solid part that will resist the calipers tendency to spread under load. Also why in StopTech’s benchmark testing, their calipers are among the stiffest in the industry.