Few things on a race car are as regularly underappreciated as the brake system. Yes, stock car racing is about going fast, but that's all the way around the track, not just the straightaway. The best braking system for your race car is one that allows you to slow the car quickly without upsetting the car so you can roll through the turn smoothly and get back on the gas as soon as possible.
Pleasing the Driver
Of course, when it comes to brakes, it's as much about finding the pedal feel the driver is looking for as it is pure stopping power. How firm do you like the pedal? How much pedal travel do you prefer? Do you like the front brakes to be significantly stronger than the rear so that the brakes will not cause the car to be loose on turn entry, or do you prefer a more balanced feel? These questions are all about making the driver comfortable behind the wheel, but they are important.
Finding the right brake balance...
Finding the right brake balance means optimizing everything from the brake pedal to the pads. Fortunately, many companies have already done the grunt work for you. Performance Friction, for instance, regularly tests all of its pad and rotor combinations with every caliper they're designed to fit.
Try to think of your brakes as a comprehensive system, from the pedal all the way to the rotors. In fact, let's go further than that: Continue your consideration all the way to the cooling duct inlets in the front bumper cover. After all, brakes that receive a steady flow of cool air will last longer and feel better late in the race than brakes that have boiled the fluid in the calipers and are only a little more effective than dragging your feet on the asphalt.
When it comes to pedal feel, the master cylinders are an important consideration. All things being equal, a master cylinder piston that is smaller will push less fluid for a given amount of pedal travel, but will create a higher line pressure. A larger master cylinder piston will have less line pressure but will push a greater volume of brake fluid, which means less pedal travel.
"The bigger the bore size you have, the more volume it pushes and less line pressure it creates," explains Derek Spencer of Perform- ance Friction. "You can use this to dial in a pressure split [balance] between your front and rear brakes. The most common setup with dual master cylinders for a typical short-track asphalt car is a 71/48-inch bore master cylinder for the front brakes and 1-inch bore master cylinder on the rear brakes.
A brake bias bar and adjuster...
A brake bias bar and adjuster assembly can provide for easy and quick tuning as to how much pressure is applied to the front brakes versus the rear. This can be a valuable tool, as conditions change a car's handling during a race.
If the driver wants more feel, you can drop the bore size-perhaps to a 131/416 in the front and a 151/416 in the rear. That will give you more feel and also a softer pedal, or more travel. That's because the smaller pistons are pushing less fluid, and it takes more pedal movement to push the pistons out of the brake calipers. If you go the other way with larger master cylinder bore, it will give you a stiffer, harder pedal. The greater volume of fluid moved by the larger pistons will require less pedal movement to move the pistons in the calipers, but because it produces less line pressure you have to push harder to get the same amount of braking forces.
"The opposite is true if you are working with the piston area in the brake calipers. A larger piston requires more fluid to move it, so it makes the pedal feel softer and requires more pedal travel. Racers will run into this when they change racing classes and run a different style of calipers. For example, I have witnessed a lot of racers have trouble when they move from Late Model Stock with the GM single-piston slider caliper to a series where four-piston racing calipers are allowed-like Super Late Model. They are used to the single, huge piston in the calipers that can contribute to a softer pedal, and when they go to a four-piston caliper, which is really better for racing, they have a hard time getting used to the stiffer pedal it produces."