We have compiled what we think is critical information about racing brakes and their application. We talked to many manufacturers and experts and this is a summary of those conversations. So as to not put an advertising face on this piece, I have left out the names and companies. Our goal is to educate you, the racer, so that you can approach your brake selection and tuning more efficiently. Let’s get started.
How do I choose brake pads for my type of racing?
Pad choice is largely determined by the type of car and racetrack. Most brake experts realize that we need to consider the type of car we are racing as to weight, center of gravity height, and size of the tire contact patch as well as the amount of grip that the track provides. We don’t want to overwhelm the tire with too much brake grip.
Because of the large selection of brake pad materials and grip levels, you should probably contact a brake pad manufacturer, chassis builder or performance parts distributor who can help eliminate guess work to get a better understanding of brake pad performance characteristics.
Does front-to-rear pad size matter?
Racers are often faced with decisions on how to regulate the brake bias between the front and rear. We need to know a little about pad sizes related to creating brake bias. When increasing the contact surface area of a pad, additional stopping performance can be attained. Many caliper manufacturers offer calipers designed for different size pads yet still allow for the caliper to mount in the same location. This allows teams to change calipers and pad size without having to change the mounting bracket and location. However, most chassis builders choose the pad and caliper combination they feel works best for their particular type of car. When it’s necessary to increase stopping performance, the calipers piston size can be increased or decreased to allow for more or less caliper pressure.
How do I break in my pads?
On the first out lap, most drivers will left-foot brake with stabs on the brake for two or three laps. In the case of prebedding, it must be done in a very controlled environment and is not recommended. While break-in procedure recommendations differ slightly between pad manufacturers, the most important aspect of pad break-in is to slowly bring the pad up to racing temperature followed by a complete cool down cycle with the car parked.
What are some solutions to bias problems?
Understanding the brake bias adjuster function is important. If used correctly the adjuster can aid a driver in many ways. For classes that don’t allow the use of adjusters, using split friction (different brake compounds front to rear) or selecting calipers with different size pistons front to rear or side to side can do a lot to solve performance problems related to bias.
What are some common problem areas during installation of pads?
In our own experience working on our various projects, as we install the brake mounts, we take special care and extra time making sure our caliper mounts were straight and parallel to the brake rotors. This ensures that the pads will be flat against the rotors and all of the surface area will be used when braking.
How long do pads last? When do I change them?
All brake pads are most efficient when they are new. Good-quality pads will perform consistently their whole lifespan. The problems come with improper wear causing pad taper. If the driver complains that the brakes are not working as well as before, change the pads.
What are the different pad materials?
Although every manufacturer keeps its materials list a secret, there are certain givens associated with racing brake pad construction. Raw materials used to produce racing brake pads include many types of metallic and nonmetallic fibers.
The particle size of these fibers plays a big role in the pads’ performance level as well as the wear of the pad and rotor. Carbon-based racing pads have become very popular because they allow for extreme temperature fluctuations while still providing good braking.
Always use pads that were designed for racing, not OE or aftermarket pads that are designed for street use. The design goals for passenger car pads are completely different from the goals for racing—they are not even close to the same. Street pads are designed to operate at lower temperatures, and that combined with an effort to reduce noise and dust makes them useless for racing.
Do pads perform better when they are hot or cold and do I preheat them before qualifying if hot is the answer?
Many fast qualifiers will drag the brake on the outlap to heat the pads. Although most pads are good in a wide range of temperature, often they need to be up to a minimum operating temperature to provide the most grip.
What are the common types of rotors and how do I choose which one is right for me?
Vented brake discs are of course considered better than single-plane discs because of their cooling properties. The discs don’t pump a lot of air through the vents because if they did, we would not see the amount of brake dust that accumulates on the wheel (the rotor would blow it away). The reason why we have curved vanes is because it helps reduce the crack propagation across the disc. It has nothing to do with pumping more air. These designs help support the cheeks (the outer portion of the disc) better. Much study goes into vane design and structure.
When choosing a rotor, you must first determine the available rotor options based on size and mounting. Next, overall weight and cooling vane configurations must be evaluated. For example, rotors with an 11.75-inch diameter and an overall thickness of 1.25 inches, are by far the most popular size used on Late Models and many Modifieds.
Above all, the most important fact to remember is that a larger or heaver rotor that has complete contact with the pad face will allow for better temperature management and longer rotor and pad life, and provide for the most consistent brake feel.
That is why standard cast-iron rotors are still the primary choice of racers in many forms racing. While exotic materials and rotor shapes have been introduced in an effort to reduce the race car’s weight, in most cases the performance of these rotors falls short compared to cast iron.
What are the best methods for checking rotor temperatures?
Temperature-sensitive paints are a good choice because you can monitor what is happening dynamically. Real time infrared sensors can be very misleading because you are only getting the surface temperature of the disc.
The surface temperature runs much hotter than the core temperature, and we should be much more interested in the core temperature. Applying temperature-sensitive paint to the noncontact areas of the rotor will give a decent analysis of actual engagement temperatures.
What are acceptable brake temperatures?
Acceptable temperatures are any temperatures warm enough to allow the pads to operate effectively and cool enough to prevent a meltdown. Since it is difficult (and expensive) to get actual, on-track temperature numbers, a post-race inspection of the pads and rotors is usually the best indicator of whether the system stayed in a safe temperature range. Excessive pad wear and/or damage to the rotor faces are telling you that the brakes were too hot.
What we don’t want to see are core temperatures above 1,200 degrees F. At that point the iron will tend to anneal, which ultimately softens the metal. From an efficiency standpoint, at least with our brakes, once the brakes see about 200-300 degrees F, they start working.
When do I want to cool the brakes? Do I always need a cooling system?
Very few instances in dirt racing require auxiliary cooling from ducted air. Most of the time, temperatures on dirt are easily managed with proper rotor selection.
Racing stock cars on asphalt is a completely different story. There are a few places on asphalt where it is possible to run with the nose sealed, but more often than not, cooling ducts are an integral part of a short track asphalt car. This is where heat is truly the enemy. Pad, rotor, and fluid failures can all result from excessive heat.
How do I plumb my cooling hoses?
First, keep in mind that you are dealing with airflow. Air does not like to make sharp bends or squeeze through tight places. Start with an inlet in a high-pressure area of the nose. The highest pressure will be on the front center of the nose. Ideally, plumb the air cooling system to direct air to the center of the vented disc rotor. Seal the other areas at the center off. The air should enter the system at the highest pressure areas of the car. Teams will sometimes come off the radiator shroud to keep from upsetting the aero efficiency of the front end.
Are rotors directional?
Yes, unless the disc is a single plane or the vanes are straight from the center out. Many times with the slotted discs the pattern will determine the ideal direction of rotation. Always check with the manufacturers for their recommendation of proper installation of the rotors.
Are rotors subject to life cycles, and how do I know when to change them?
A visual inspection of the rotors should be a part of all routine weekly maintenance. Wear, as long as it is smooth-faced and even, is not necessarily a reason for alarm. Rotors with light surface cracking in the contact face can also be run as long as the cracks don’t begin to open. Rotors with structural cracks or heavily scored faces should be immediately replaced. All rotors will experience some thermal fractures through the life of the rotor. When these cracks exceed 6-8 mm in length it is time to replace the rotor.
A good rule to follow is to measure the new rotor face thickness upon installation, then during weekly maintenance check the thickness. The rotor should be discarded when the thickness of the face becomes less than half what it was originally.
Rotors should be put through the same type of break-in procedure as brake pads. This will decrease the likelihood of warping and cracking. Most rotor manufacturers advise against altering the rotor in any way, including turning the rotor down to remove uneven wear and groves. Lightly sanding the rotor surface by hand to remove excessive buildup of brake pad material is acceptable.
How do I match my brake system to the type of racing I do, such as dirt or asphalt, touring to one-track racing?
Work with your brake professional to match your system to your type of racing. Develop a technical partnership between the team and the professional. They are there to help you get the most out of your system. It does the brake company good to see you do well with their products, so they have a high interest in your success.
Effective heat management, overall stopping power, and engagement response are the primary requirements of any brake system at any event. A driver can compensate to a degree for less than perfect response or overall stopping power, but when the system becomes compromised by heat, a DNF or poor finish is usually the result. The bottom line for any brake system is that it must have sufficient cooling capacity for the event.
Optimizing a car for a specific track can be easier but still may give room for package tuning. Considerations regarding qualifying setups and race setups, or short race versus long race setups, should always be given. Sometimes the challenge is finding what is necessary for the brakes to survive an event.
With some teams, regardless of the type or style of racing, the first consideration should be: What are the performance characteristics the intended type of racing requires of your brakes, and what limits of the rules might allow us to maximize the brake components? Traveling teams would be wise to use components that allow interchanging brake calipers and rotors for optimum brake package tuning.
The overriding theme presented here is to (1) make sure your brake system is properly installed, (2) let your brake professional help you to put together the proper brake package for your type of racing, (3) always do the proper maintenance on your brake system to prevent failures, and (4) most of all, do not be shy about contacting your brake professional when you have a question or need help. They are there to assist you. The better your team does, the better it is for the company the team represents. Think smart, race smart, and don’t be afraid to ask questions of those who are smarter than we. After all, that is the best way to learn and get better.