Monday, October 17, 2011

obp Tech-Session - What is Special About Race CarBrake Fluid.

Brake fluid is the precious fluid in a brake system. This brake fluid is the solid/physical connection delivering the force you exert on the brake pedal to the brake calipers. The basic premise is the brake fluid is non compressible thus being able to exert the correct force through the brake lines and to the calipers.

One of the enemies of brake fluid is heat!! If enough heat is transferred into the fluid and is able to boil the fluid, this will result in brake fade. Also leaks and air in the system will result in the pedal travelling too far and you will  lose the pressure you have generated to stop the car.

A very important thing to keep in mind is when you purchase brake fluid they are not all the same. You can get Poly-glycol Ethylene and Silicon based.

Poly-glycol Ethylene based:

The key ingredient Poly-glycol Ethylene has high lubrication properties to lubricate the rubber parts. However this ingredient is not susceptible to boiling.

Poly-glycol Ethylene based brake fluid is hydroscopic meaning it has the ability to mix with water and still perform adequately. However water will drastically reduce the boiling point of the fluid. In a passenger car this is not a problem however in a race car it is a major issue, as when the boiling point decreases the performance ability will also decrease.

Silicon based:

The other option is Silicon based fluid. This type is used mainly in military type vehicles and because silicon based brake fluid will not corrode and damage paint work it is used in some show cars.

This type of fluid is highly compressible and can give the driver a feeling of a spongy pedal. The higher the brake system temperature the more the compressibility of the fluid and this increases the feeling of a spongy pedal.

Silicon based brake fluid is non-hydroscopic. This means that the oil does not mix with water. When water is present in the system it will create a water/fluid/water/fluid. Because water boils at approximately 212F the ability of the brake system to operate correctly decreases and the steam from the water creates air in the system. It is important to remember that water may be present in any brake system. Therefore silicon brake fluid lacks the ability to deal with moisture and will dramatically decrease a brake system's performance.

Poly-glycol Ethylene type brake fluids are two times less compressible than Silicon type fluids. Less compressibility of the brake fluid will increase pedal feel. Changing the brake fluid in a race car on a regular basis will greatly increase the performance of the brake system.

Brake fluids are rated by the DOT speccification. The most important characteristic of any brake fluid when used in a race car is the boiling point. A high boiling point is necessary for racing applications due to the massive heat build up in the rotors that is transferred through the calipers to the brake fluid.

The maximum boiling point is important when selecting a fluid for a race car. The minimum dry boiling point should be 500 F, higher if possible. The standard DOT types are not really adequate.

Brake Fluid Type                  Dry Boiling Point                  Wet Boiling Point

Dot 3                                                 401F                                    284F

Dot 4                                                 446F                                    311F

Dot 5                                                 500F                                    246F

Dot 5.1                                              518F                                     375F

Wet Boiling Point: The minimum temperature that the brake fluid will boil when the fluid has 3% water by volume of the system.

Dry Boiling Point: The temperature that brake fluid will boil at with no water present in the system.

It is always best to use the correct and race specific brake fluids in your race car. These are a few to have a look at.

ATE Super Blue/TYP 200. Super Blue is a very high performing brake fluid. A mainstay in German automobiles, Super Blue is arguably the best value for your money in brake fluid.

Dry: 280C (536F)
Wet: 204C (388F)

Brembo LCF600. LCF600 is the newest brake fluid on the market. Excellent choice for track use with proven low compressibility. It gives a firmer pedal feel than most other brands.

Dry: 316C (601F)
Wet: 204F (399F)

CASTROL SRF. The SRF is the absolute best brake fluid on the market, period. If you want the best, then Castrol SRF is it due to its extremely high dry & wet boiling points.

Dry: 310C (590F)
Wet: 270C (%18F)

MOTUL RBF600. The world's best selling brake fluid. Developed for all forms and levels of racing, the RBF600 is one of the most popular fluids on the market today.

Dry: 312C (594F)
Wet: 216C (421F)

APRacing 600 Brake Fluid. AP600 Fluid has been developed for racing applications where higher than normal temperatures are being experienced, e.g. when using carbon/carbon discs and the ultimate in brake fluid performance is required.

Dry Boiling Point in excess of: 312C (594F)
Wet Boiling Point: 204C (399F)

It is imperative you bleed your brakes before every event. Most top race teams remove the old fluid and replace it with new before each race. Doing this is the only way you can be 100% sure the fluid has not absorbed any water and you will get the best performance out of your brakes.

It is also a good idea not to buy fluid in large containers and when the fluid is exposed to the atmosphere make sure it is for the shortest time possible.

What You Should Do and Never Do With Race Car Brake Fluid!

    * Never use standard Silicon based fluid in a race car brake system
    * Using racing specific brake fluid will increase brake performance
    * Never mix different type or brands of brake fluid
    * Use small fluid containers that can be used quickly
    * Always make sure the reservoir tops are tightly secured
    * Purge the system (drain completely) and replace fluid often
    * Immediately replace the reservoir cap after any maintenance
    * Always bleed brakes before all events

I hope this has been useful to you.


1 comment:

Graeme said...

Obviously wouldn't mix types of brake fluids, but why not brands? Often see statements that you shouldn't, but never reasons for this. If the stuff mixes with water, surely it should mix with another brand!