by Brian Berk ©2002
Modern racecars need good brakes. Good brakes will allow you to drive faster. High performance brakes have improved tremendously over the years with Formula 1 and GT leading the way using the latest carbon/carbon brake technology. The Formula One world champion, Mika Hakkinen, once was quoted saying The most important thing in a sports car in not the engine but the brakes.
There are many types of rotors available for racing applications such as steel, cast iron, carbon/sic, carbon/carbon to name a few. Rotors can be solid, vented, drilled, or have slots on the friction surface.
Cast iron rotors are the most common and readily available for many applications. Cast Iron rotors should not operate at a bulk temperature over 610 C and above 3000 rpm.
Carbon/carbon composite rotors perform well at high temperatures, much lighter (less rotating weight and unsprung weight) and are very expensive. Carbon is typically used in F1, GT, and is showing up more in drag racing, motorcycle and Champ cars (depending on regulations).
Brake Pad Notes:
Brake pads typically wear more on their leading edges. High end multi-piston racing calipers have smaller pistons on the front going to larger pistons on the back of the caliper to even out brake pad wear.
Pad break-in or bedding: always break-in according to the manufactures recommendations. They spend hours testing on brake dynamometers to develop procedures for bedding the pads. It is not the best practice to race with new out of the box pads.
Use a DOT 4 with the highest boiling temperature that is available. Some race fluids have a boiling temperature of over 600 F.
Limit the exposure to the atmosphere. Brake fluid will absorb water which will lower the boiling point. With moisture in the fluid the boiling temperature can be reduced to the 212 240 F range.
It is a good practice to flush the brake system with fresh fluid after a race that required hard braking. Once the brake fluid has been very hot or near the boiling point, the boiling point can be lowered.
If time permits, a great way to bleed is gravity bleeding.
Open all 4 calipers with master cylinder full
Use clear tubes off each bleeder into a drain pan on each caliper
Bleeders should should be pointed up for this to work properly
Watch for bubbles in the tubes. Once there are no more bubbles, close the bleeders tight.
Brakes convert kinetic energy to heat. KE=1/2 MV2, or the amount of heat generated increases by the square of the increase of speed (V). The faster you go the more heat the brakes will generate.
Cast rotors should not operate at a bulk temperature over 610 C
Caliper temperatures should be kept well within the working range of the brake fluid to prevent fluid vaporization and loss of braking.
Peak fluid temperatures should not exceed 240 C or operate over 200c for over an hour. Either case the seals will most likely need replacing.
Stainless is a good choice for pistons due to slower heat transfer than mild steels.
For optimum performance, operate at the correct brake temperature (refer to manufacture recommendations). All discs should operate at similar temperatures front/back and side to side (balance).
Use temperature paints or stickers to monitor or investigate rotor, pad or caliper temperatures. When testing for brake temperatures it is important to complete several laps in succession (say 10 laps) at race conditions.
When using ducted air for cooling, most of the air flow should be directed up the discs vents. It is important not to overcool, but keep enough air flow to keep the temperatures stable within the working range.
Project Engineer, Honeywell Aircraft Landing Systems
* Article by Brian Berk. Visit http://RacingArticles.com for more "how-to" on Racing.
© 2005 - 2007
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Drilled rotors offer improved bite but are more prone to cracking more so than grooved or solid discs. Rotors should be discarded of cracks emanate from the mounting holes, slots, ID or OD. If in doubt, change the rotors to be safe. It is not worth the risk of a rotor failure to save a few bucks
A grooved disc improves cleaning of pad surfaces and provides more consistent brake performance and longer life than cross-drilled rotors.
Runout: With the rotors on the racecar, the runout should be less than 0.005
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