What Is Brake Fluid In A Race Car? Motorsport Tech-sessions

Hello, how are all you motorsport nuts doing?

Today I want to talk about Brake Fluid and what is the best fluid to use in your race car.

Brake fluid is the precious fluid of 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 to far and loose 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 Polyglycol Ethylene and Silicon based.

Polyglycol Ethylene based:

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

Polyglycol 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, due to 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 212 F the ability of the brake system to operate correctly decreases and the steam from the water then 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 decreases a brake systems performance.

Polyglycol 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 specification. 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 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.

DOT Brake Fluid Type

Dot 3 – Dry Boiling Point 401F – Wet Boiling Point 284F

Dot 4 – Dry Boiling Point 446F – Wet Boiling Point 311F

Dot 5 – Dry Boiling Point 500F – Wet Boiling Point 246F

Dot 5.1 – Dry Boiling Point 518F – Wet Boiling Point 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 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 main stay in German automobiles, Super Blue is arguably the best value for your money in brake fluid. Dry: 280°C (536°F) Wet: 198°C (388°F)

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 then most other brands. Dry: 316°C (601°F) Wet: 204°C (399°F)

CASTROL SRF The SRF is the absolute best brake fluid on the market, period. If you want the best the Castrol SRF is it. Due to it’s extremely high dry & wet boiling points. Dry: 310°C (590°F) Wet: 270°C (518°F)

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 fluid’s on the market today. Dry: 312°C (594°F) Wet: 216°C (421°F)

AP Racing 600 Brake Fluid AP 600 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 are required. Dry Boiling Point in excess of: 312°C (594°F) Wet Boiling Point: 204°C (399°F)

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 have 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 and Never Do In A Race Car!

# 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 fluidUse 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 maintenanceAlways bleed brakes before all events

Thank you for your time.

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