Project EVO X Part 2, Making Great Brakes Even Better!
By Mike Kojima
When we last worked on Project EVO X we installed a very comprehensive yet very streetable suspension system from KW and Whiteline. In continuing our theme for building the ultimate EVO X without compromising its daily driveabilty, we now turn our attention to the brakes, wheels and tires.
The EVO X comes with pretty good brakes from the factory, big Brembo 4 piston front and 2 piston rear calipers squeeze big 13.8″ front and 13″ rear rotors. The front rotors are 2-piece floating type with alloy center hats and anti rattle clips. In other words the stock brakes are already quite good, what would have been state of the art just a few years ago. So why would we want to change them out with something else? The main reason is that since our car is going to see some occasional track use, we want to upgrade our brakes so we can drive our car to the track for an event without the hassle of having to switch pads at the track. The big brakes will allow us to run at speed on a streetable brake pad. Bigger more powerful brakes will also be easier to modulate. The third reason is admittedly that big brakes just plain look cool!
|When comparing the stock brembo 4-piston caliper to the much larger Stoptech STR caliper, it is easy to see that the Stoptech part can accommodate a much larger brake pad.|
We chose Stoptech as the brake system of choice for its combination of daily driveability and track performance. We selected Stoptech’s Trophy STR big brake kit. The Trophy kit features an enhanced version of Stoptech’s venerable ST-60 six piston front calipers and ST-40 4 piston rear caliper. The Trophy calipers feature a forged aluminum alloy body. Forging is a superior method of forming aluminum when an aluminum billet is heated and basically smashed into shape using many tons of force into a die. Forging produces a part with compressive stress for increased strength. It also orients the metal’s grain in alignment to the part’s shape. Putting the grain in the right direction increases strength and dimensional stability, much like how putting the grain of a piece of wood in the direction of stress makes for a stronger wood part. The pressure and stress of working the metal during forging also refines the aluminum’s grain making it finer and eliminating voids and other internal flaws that can weaken the structure. This also makes for a much stronger part.
|The rear 4-piston Stoptech caliper is considerably larger than the 2-piston Brembo part|
All Stoptech calipers are forged but the Trophy STR calipers are additionally shaped optimized using finite element analysis or FEA. FEA allowed Stoptech’s engineers to figure out where material could be pared from the caliper body without affecting stiffness. These areas were then hogged out using a CNC machine for a 20% reduction in caliper body weight without any loss in rigidity. A stiff caliper is important because it makes for a firmer brake pedal with better feel and modulation. After machining, the STR caliper bodies are hard anodized for a tough corrosion resistant finish. Hard anodizing is an electrically converted surface of aluminum oxide that is thicker and harder than regular anodizing. Aluminum oxide is used as an industrial abrasive so you can imagine how hard this is.
|The Stoptech STR caliper has a bridge assembly, (the black part in this picture which greatly increases the stiffness of the caliper). The silver things bolted to the bridge are anti rattle clips. They preload the brake pads reducing noise and brake squeal. Note the CNC milling of the caliper that reduces weight making the STR caliper weigh about 20% less than the standard Stoptech ST-60 caliper.|
The STR calipers use standardized FMSI D1247 front and FMSI D372 pad shapes shared with Brembo, AP, Alcon and other common racing brakes. The important part about this feature is that this means that there are many pad choices from many manufacturers in this size so the end user can select pads from a pool of at least 15 different compounds. The calipers have a bolt in bridge to span the open area of the caliper where the pads are inserted which greatly contributes to caliper stiffness without contributing to additional bulk and weight. The STR calipers are also equipped with stainless steel abutments that the brake pad backing plates can ride upon to prevent them from gouging into the softer aluminum caliper body in long term use. The smooth hard stainless also makes the brake action smoother with a more consistent pedal as the pads can move more freely when the brakes are applied.
|The light gray brake pads are the Stoptech parts, note that they are much larger than the stock Brembo pieces. More pad area = more stopping power.|