DPI has a new rotor design--it...
DPI has a new rotor design--it has scalloped the rotor. This reduces the weight and some of the moment of inertia. This manufacturer has taken a 9-pound rotor and made it 5.5 pounds.
Dirt racers should use smaller piston calipers on the front and calipers with bigger pistons on the back. Some dirt chassis builders run the same size caliper on each corner, but use big pistons on three corners and smaller pistons on the right front. Before buying any brake components, check with the brake manufacturers for their latest recommendations.
Ducting
Getting air to the rotor is critical to extending pad wear. The hotter the rotor gets, the faster the pads wear. The racer wants to get as much air as possible to the rotor. Run the biggest duct possible without interfering with the suspension travel. It needs to be as straight as possible and run into the plenum, or center of the rotor. Rotors pump air from the inside out. A second duct can dump air on the surface of the rotor.
DPI's Dan Press says, "We have worked with racers who were losing their pedals at the end of a race. For the next race, the only change they made was to add a brake duct. That solved their brake problem. The key is to get as much air blowing through the rotor as possible to cool it off."
Use a high dry boiling point...
Use a high dry boiling point racing-brake fluid. Change it before every race. Once the can is opened, the fluid starts attracting water and begins to lose its boiling point. The lower the boiling point of the brake fluid, the quicker your brakes will fade.
Brake Fluid
Change your brake fluid before every race! In order for the brake system to work its best, you must have a brake fluid with the highest boiling point possible. Begin with a racing brake fluid like AP 600, AP 550, or Wilwood 570. They all have very high dry boiling points--around 570 degrees F. The dry boiling point is the minimum temperature at which the fluid in a sealed bottle, in its most uncontaminated state, will boil. The racers should be concerned with the dry boiling point--not the wet boiling point mandated by DOT rules. The wet boiling point is when the fluid cannot absorb any more moisture. At that point, the fluid cannot boil at a temperature lower than 284 degrees. DOT 3 fluid has a dry boiling point of only 401 degrees F.
All brake fluids absorb water. Water gets into brake fluid from humidity, washing your car, and from natural condensation when the fluid gets hot and then cools. As water accumulates in brake fluid, it slowly deteriorates the performance of the fluid. It lowers its boiling point. When the fluid heats up, it expands. This gives you a spongy pedal and brake fade.
Only buy brake fluid in small sealed cans. If any fluid remains after topping off the system, toss it. Do not try to save the small amount left in the car. It will become contaminated while sitting on the shelf. The most common complaint is "My pedal is spongy." This problem can be remedied by changing the brake fluid before every race.
Wilwood's Doug Burke cautions racers, "DOT 5, silicone brake fluid should not be used in racing. It is highly compressible, due to the fact that aeration occurs very easily. It is not hygroscopic, so water will accumulate into little drops, and at high temperatures will turn to steam and expand. You can actually get a little brake drag because the fluid is expanding and putting pressure in the pads. At the high temperatures in racing, you will get a spongy pedal."
Because racers use the biggest-diameter...
Because racers use the biggest-diameter rotors possible for more brake leverage, very little air comes through the wheel to cool the brakes. Ducting cool air from the front of the car is mandatory. One hose should go to the plenum, or inside center of the rotor. Rotors pump air from the inside out through the vanes. Additional ducts can direct air to the surface of the rotor to cool it.
Maintenance
How do you know when it is time to replace the rotor? Dan Press at DPI and Sierra Brakes answered, "As soon as you start feeling some ridges on the surface, take them off. You will see a wear pattern developing. If you catch it early, the rotor can be blanchard-ground five to ten thousands. This will make the rotor as good as new.
"I don't like turning the rotors. A blanchard grind takes the surface molecules in different directions. It is not going in just one, as on the brake lathe. With a lathe, you are already putting grooves on the rotor. The pads will follow that groove when breaking it in. When you grind them, the pad will wear more evenly.