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.