Brake Tech

Racing would be so much fun if it weren't for motors, tires and brakes.  All three lose life expectancy exponentially to the level of fun you are having.  Further, just like an engine that is abused with over-revving, brakes can be easily abused as well.  The difference though is in the fact that an engine can have a prescribed set of parameters to operate for a given output/lifespan ratio.  Rev limiters, gauges and lights can aid the driver in keeping the engine together.  Whereas current brake technology requires the driver alone to moderate rotor and pad life by operating within the varying parameters required. This is not easily learned by everyone.   I started racing when brakes were junk compared to today, I always had to favor them with driving technique.  Today, driver’s of heavy high powered cars that want good brake life need to learn to manage their brakes as well.  I also learned that driver aside, most brake problems are a result of chassis problems.  If you have a properly set up GR40, then we at Griggs Racing know the chassis can be ruled out and that just leaves the driver. 
What we have found with drivers that have rotor problems is:

1)Most do not understand the bedding process.

2) Most do not understand that threshold braking is NOT the fast way around a track in a heavy car.

3)Most do not understand how to warm and cool their brakes.

4)Most do not understand how to, or cannot balance the brake bias and run too much front bias.

5)Most all have power assist.
All of us in the performance world seek BIG NUMBERS because with the exception of weight, BIG is usually FAST.  However, BIG has some mathematical rules attached.  The BIGGER the power number, and more than anything, the BIGGER and stickier the tires, the BIGGER the MPH indicator at the end of the straight, the BIGGER the amount of energy your brakes have to dissipate. Another mathematical rule of BIG is; how BIG your eyes get as you charge into that corner is directly proportional to the amount of pressure you place on that brake pedal.   If scaring yourself is the aim, you will pay for it in brakes.  This is exaggerated with a power assisted heavy street car on most any track.  How do we control the destructive power in our foot?  Just like we save the engine by not over revving, DON’T OVER BRAKE.

It is important to understand the bedding process of high temperature pads.  It is important to raise the temperature of a brake rotor slowly and cool it slowly.  It is important to understand what too hot is, and how much pressure and for how long you can run your brakes hard.  It is especially important to understand what properly unbalanced brakes feel like, so you can keep yours balanced.  About 20% of the energy you pour into your gas tank will eventually be absorbed into your brake rotors if you use them as hard as you can.  A 5oohp 3500 pound car uses about a gallon every 3 miles on a moderate speed road course.  That means you are pouring about a quart of burning gasoline into your wheel wells every lap. Have you ever seen how much fire and heat a quart of gas can make?

Thermal treating of metals is not an exact science and engineers that design stressed metal products search out and rely heavily on the experience and expertise of a good industrial heat treater that has mastered the art form of stress relieving and stress inducing thermal processes.  Yet, every time you use your brakes on a race track you are heat treating them for better or for worse; you can either stress relieve, or induce stress, depending on your foot.  In most cases, cracking is caused by thermal shock; two rapid or irregular an increase or decrease in temperature.  Varying characteristics in track configurations, traffic, ambient conditions, and performance demands make this an art form for the driver to master, and even in the pro ranks few get it right all the time.  

Bedding is super important, but I am not going into that here. I’ll save that for the referenced article below.   After bedding them properly, do what the pros do, the good ones.  When you go out on the track, use at least one if not two laps to warm up the brakes, gently at first.  Not just so they will work, but so that they are warmed up progressively.  And really important is after the checker flag.  Do not just get off the gas, and gradually slow down without using your brakes.  Your brake ducts are still working and unless you apply pressure to the middle pedal you can shock the rotors with too rapid cooling. 
 The faster the car goes the faster the rotors cool due to airflow, so slow the car way down using the brakes and them gradually reduce your usage of them  during a slow cool off lap, slowly reducing the pressure as the lap unwinds.  When you stop NEVER sit with your foot on the brake.  I know some smart drivers that drive around the paddock as their brakes cool to prevent irregular cooling that can occur when the car sits.

 When you are driving, never threshold brake repeatedly if you want good life, and good performance.  I never threshold brake at all, unless it is the only way to make a pass, and that is rare.  “Glide in, Power out”  is the way to make good lap times in a heavy high powered car and generally is the best way to position for a competitive pass. 

Design and structure of the rotor is another factor.  We believe in using the lightest and smallest diameter rotors we can get away with for the job to reduce moment of inertia and unsprung weight for the obvious advantages.  However, if all things are being done right, and rotors still fail, then the trade off in weight for a heavier rotor should be considered. 

I am often heard making the statement that auto racing is the same as going to war.  If both sides have the same resources, the one that manages his resources best wins.  My experience winning races has been with very few brake problems.  Early in my career I got into a late model stock car that at first terrified me because it was so hard to stop.  The pedal felt like pushing on concrete, and the car just didn’t feel like it would stop.  Complain as I did, the old crew chief would just smile and say “You go fast with the throttle, not the brake.”  I felt like if an emergency on track occurred I couldn’t stop.  I can’t remember how many races we won with that car, but it was many, and it did stop when I needed to.  I learned from that experience that I was over braking almost all the time in my own cars. After that I decreased pedal leverage in my cars and in cars of many others and though all then complained about the brakes, they all went faster.  These were all manual braked race cars.  Power assist is much harder to deal with if you are trying to go fast.  We need a booster on the street for when the brakes are cold, but on the track when I drive a car with boosted brakes, I have to constantly remind myself to press really easy on the pedal so as to not over brake.
Know how hot you are getting your rotors.  Use the commonly available thermal paints which usually come in green orange, and red.  If you are burning off the red color,  then expect short brake life.

To sum up:
 The faster the corner is taken the less you have to slow for it. Chassis problems mean slowing more for the turn, more brake is needed. Threshold braking upsets the chassis inducing understeer and therefore more slowing is needed to make the corner, exacerbating brake abuse.  Use it only when you have to overtake. Power boosters not only induce over braking, but reduce modulation, and therefore finesse is thwarted.  What a driver perceives as fast with confidence may not be.  If a car is comfortable to stop without feeling your leg muscles working hard, it is not suitable to race.

There is no such thing as a “warped” rotor.
Carroll Smith wrote the book on brakes for drivers to understand and dispels the myth of warped rotors.  In the ‘60s Smith was involved in what was probably the largest disc brake development campaign in road racing history on the Ford GT40 for Shelby American and Kelsey Hayes with some of the best drivers in the world at that time.  His document is very complete and concise, except it predates the current ceramic carbon pads we use on race cars today, which are harder still on rotor life when brakes are power assisted and/or abused. 

If you understand the physics involved and take care of your brakes, they will take care of you and reasonable life can be achieved.