The main focus of drag racing is to go as fast as you can to reach the finish line … but that’s just part of the race. You still have to bring your vehicle safely to a stop when the pass is over. The stopping portion of the race presents some unique challenges in drag racing because racers want to save weight, and that can make designing brakes that get the job done without excessive bulk a tricky process. We sat down with Randy Cotteleer from TBM Brakes to talk about their unique Revolution rotor design and how it works in a drag racing setting.
The braking process, of course, begins the second you step on the pedal and hydraulic pressure is applied to the braking system. The master cylinder in the braking system creates pressure, and it sends that throughout the brake lines before it reaches the calipers. That pressure, when it reaches the calipers, causes the pistons inside to generate force that moves to the brake pads. When the pads receive the pressure from the pistons , they clamp down on the brake rotor and bring the car to a stop.
Drag racing still requires a vehicle’s braking system to operate under the same principles of a passenger car’s system, but it has a different set of demands. The standard wheel and tire package on a car used in drag racing has a smaller set of tires in the front with larger ones in the rear. This changes the dynamics of braking for the vehicle. With the smaller tires in the front, the lion’s share of braking force must be transferred to the rear of the car to provide stability.
Because drag racers are always looking to save as much weight as possible, the components they select for their braking systems are smaller and lighter than those found on street cars or in other forms of auto racing. All of the rotating parts, like the rotors, have any unnecessary material removed since they don’t worry as much about longevity, or have a need for the rotor to cool down from multiple high-speed stops in a row. The calipers and pads are smaller to save weight and fit within the smaller drag racing-style wheels. All of these parts are also made of more aggressive compounds to produce more friction for better stopping power and allow them to work better at higher temperatures they see at the track when they’re being used.
The TBM Rotor Design For Drag Racing
For over two decades, TBM Brakes has been developing braking systems for different forms of racing. The inspiration for their Revolution rotor that is used in their drag racing line of products actually came from their sprint car racing brakes. Sprint cars require brakes that have excellent stopping power, but are ultra-lightweight and have a high level of durability. “Adapting the design to the drag racing market was natural. The needs of the sprint car market align well with the drag race market from a rotor perspective,” Randy says.
Developing the design of the Revolution rotor went deeper than just selecting an interesting shape. The team at TBM completed a complex analysis and design process to get the best possible rotor for drag racing applications.
“The first thing we did was calculate the thermal demands of the system. We have several computer models we use to calculate the mass required to optimize braking performance in a given set of circumstances. Next, we fix the outside diameter and mounting pattern of the rotor to fit in the packaging confines for a drag racing application inside the smaller wheels. Then, we use the convolution and drill pattern to get to the calculated mass. By doing all of this beforehand, it creates a rotor that is the correct weight and dimension for the system, while still having a high level of performance,” Randy explains.
Because we are able to take weight out of the rotor with the shape, along with the fact the design allows the rotor to stay flat during temperature changes, we can run a larger diameter rotor. – Randy Cotteleer
Brake rotors have special material requirements that play a key role in how they function and wear under extreme use like a drag racing application. Generally, brake rotors are made from either cast iron, titanium aluminum, or steel.
For drag racing, cast iron isn’t the best choice, because when it’s used in thin sections it has the tendency to crack at higher temperatures, and that is increased when you try to drill cooling holes into it. Both aluminum and titanium have exceptional wear characteristics when they’re not coated; but if they are coated, they require extra maintenance with grinding and recoating. These factors, along with their expense and shortened lifespan, make aluminum and titanium an unsuitable choice for drag racing rotors.
Taking all of these factors into consideration when it comes to their rotor material choice, TBM elected to use a high-quality steel for the Revolution rotors. This allows them to provide the best option to address all the requirements that drag racing rotors have.
“Looking at all the materials out there, steel made the most sense to us with the Revolution rotors. Steel maintains its strength at elevated temperature better, provides excellent friction and wear characteristics, and is not prone to cracking or catastrophic failure under the conditions we subject it to in drag racing,” Randy says.
To help the Revolution rotor function as it was designed, TBM needed to go through a process of compromises to get the ideal size. A big rotor that is thicker will provide plenty of stopping power and be able to resist warping, but that adds more weight to the rotor, going against what you want to do when designing a brake rotor for drag racing.
Randy provides some insight on what TBM did to overcome their rotor sizing issue.
“For the rear rotors, we knew that to maximize braking power, we were going to need the largest diameter rotor that would fit inside of a 15-inch double beadlock wheel. That left us with a rotor diameter of 11.50 inches when using the TBM Caliper. This is slightly larger than some of our competitors because our calipers are slimmer over the top. We also knew that we needed a rotor mass of 3.3 pounds to meet our performance requirements. That led us to a thickness of .360-inches—thin enough to make weight, but because of the benefits of the Revolution shape, still thick enough to be dimensionally stable.”
The front rotors required a similar process, Randy shares.
“For the front, we needed enough room to get the caliper out away from the wheel and hub assembly while providing clearance for the spindle. This requires a 10.75-inch rotor. Given that outside diameter, we calculated a rotor mass of 2.6 pounds. We were left with a rotor thickness of .205-inches—too thin to be stable using our standard convolution/drill pattern. This caused us to change the pattern to take more material out of the face. We then replaced the lost mass by thickening the rotor to .285-inches, bringing the weight back up to the 2.6-pound spec.”
Low Maintenance Brakes
TBM’s Revolution rotors still require maintenance like any other brake rotor. To keep them in the best shape possible, scuffing them with 80-grit sandpaper is suggested by TBM. This process is also recommended by TBM if you experience parachute failure and have to really stand on the brakes. A simple inspection for glazing and another scuffing with the 80-grit sandpaper is all that’s needed to repair the rotors after an instance of hard use.
“The caliper design is the key to the system we decided to use with the Revolution rotor. While the caliper maybe a few ounces heavier, the overall kit weight is reduced because we use a lighter rotor, which takes weight out in the most advantageous way: rotating weight. Its stiffness creates performance, but also allows for the other components to be lighter, enhancing performance without risking safety. All of this ties back to the design of the Revolution rotor and its unique design,” Randy says.
The Function Side Of The Revolution Rotor
Having a braking system that’s able to take a large amount of punishment and not experience any serious issues adds another layer of safety to any racecar. Drag racing can be particularly hard on brakes, considering how they’re expected to assist in holding the car at the starting line before the race begins, help slow the car down with extreme precision in a bracket racing scenario, and bring the car to a stop quickly after the race is over when the car is traveling at a high rate of speed.
The Revolution rotor combines its eye-catching design, engineering, materials, and proprietary coatings to create a high-performance braking system when combined with its other parts.
“It’s really a systems-based approach. The stiffer calipers and race-spec pads allow racers to run lighter rotors like the Revolution, which enhance performance. The calipers stay stiff, even when they get hot, and the pads have a broad temperature range, so even in the event of a parachute failure, you can rely on your brakes to keep you out of the sand. The Revolution rotors are the backbone of the entire system with their design that assists them to perform so well in these harsh conditions and provide a consistent braking feel, pass after pass,” Randy explains.
Going with this larger rotor adds a nice increase to braking power, while not sacrificing performance by adding rotating weight. – Randy Cotteleer
Heat is the enemy of any brake rotor, and it can lead to brake fade and even failure in extreme cases. When slowing a car down that could be running in excess of 200 mph, a large amount of heat will be generated, so TBM made sure the Revolution rotors could fight the heat while still bringing a racecar to a stop quickly.
“There are several facets to the Revolution rotors that help them deal with the heat. First, the steel we use is able to withstand higher temperatures than cast iron will. This is important because the very lightweight rotors we see in drag racing can see temperature spike in excess of 1,400 degrees Fahrenheit at the end of a pass when braking is at its heaviest.
“The second factor is the thermal processes we put the rotors through when they are being made. This relieves internal stresses and adds toughness to the base material we use to create the Revolution rotor. By following this process it can prevent the material from moving as temperature changes when the rotor is being used.
“Third, and most important, is the convoluted shape of the rotors we use in their design. This creates a consistent thermal cross section, so the rotors heat up evenly across the entire friction face. The issue with a solid disc rotor is that the outside edge, because it is moving faster, heats up more than the inside of the rotor. This causes the outside to grow more than the inside and create the “coning” or “beveling” that we see on full disc rotors. The convoluted shape prevents this, which reduces drag and heat input allowing them to stay much cooler overall,” Randy says.
The reduced amount of material in the Revolution rotor plays an important role in how it functions as a part of the overall braking system. By lowering the weight, there is a certain level of performance gain that occurs and that works well with the lower drag provided by the rotor along with an extended lifespan.
“Because we are able to take weight out of the rotor with the shape, along with the fact the design allows the rotor to stay flat during temperature changes, we can run a larger diameter rotor. Going with this larger rotor adds a nice increase to braking power, while not sacrificing performance by adding rotating weight. All of this lets the Revolution rotor do more with less, and, at the same time, not give up any stopping power,” Randy explains.
The Revolution rotor by itself is a great piece of braking technology for drag racing, but it still has to function as part of the TBM braking system as a whole. Everything that TBM built into the Revolution rotor was designed to work with the rest of their braking system, and that’s what makes the rotor so special.
“Everything we packed into this rotor comes back to a systems approach in brake rotor design. Our calipers are stiffer and have less drag, so they put less heat into the rotor. The brake pads have a wider operation range, so they can withstand higher temperatures without sacrificing cold bite. Because the pads can take more temperature and the calipers create less heat, we can run a lighter rotor. We are able to run a lighter rotor because the design and engineering of our Revolution rotors allow them to withstand temperature and stay flat, which prevents drag, which improves performance,” Randy explains.
TBM decided to go above and beyond in the design process of their Revolution series of rotors for drag racing. The careful thought and design put into these rotors are what makes them have such a unique look and makes them work so well in the drag racing environment. By thinking a brake rotor is more than just a metal disc, TBM created a product that provides a high level of performance for any drag racing application.