Jeff Eicher, brake specialist for Joe Gibbs Racing, works on the new Alcon design calipers.
“Racing in today’s NASCAR circuit is more competitive than ever. With the field so evenly matched, an advantage like better braking can easily make the difference between winning and losing.” So says Jimmy Makar, senior vice president for Racing Operations with Joe Gibbs Racing.
What are the challenges in designing a NASCAR brake system? A vehicle in motion accumulates kinetic energy proportional to its mass and to the square of its speed. So to stop that vehicle or to even just slow it down, that energy has to be transferred somewhere else. The easiest method is to convert that kinetic energy into heat, and that’s exactly what braking systems do through friction between the pad material and the rotor. The vehicle we’re designing for is a 3,400-pound, 800 hp rocket ship capable of speeds of nearly 195 mph. That’s a lot of energy to convert!
And not every track is the same. In fact, many engineers designate NASCAR venues as super speedway, intermediate tracks or short tracks. Road courses like Watkins Glen fall into the short track category. Each has its own braking challenges. Super speedway cars, for example, use pad and rotor combinations similar in size to conventional passenger car systems. Other than avoiding the “big one,” these brakes aren’t called into use very much. Their biggest challenge is slowing that 195 mph car down to pit road speed in just a few seconds.
This shows (in red) how much more downforce is exerted on the COT (foreground) versus the old style stock car (background).
Because the brakes are cold when applied, it’s not unusual to see cracks in the rotors from the thermal shock load incurred. Speedway systems are built as light as possible to reduce unsprung weight and improve handling. They also are designed to produce near zero drag when the brakes are off, using special caliper seals and pad retraction springs. This adds to overall speed and increases fuel mileage, a factor that has determined the winner of more than one super speedway event.
Working With a ‘Paper Clip’
On the other side of the spectrum is Martinsville, better known as the “Paper Clip” to the teams that compete there. It is a half-mile oval shaped like, well, a paper clip, with two 800-foot long straights. Cars run up to 120-plus mph before stomping on the brakes and slowing down to 60-plus mph. On a 500-lap race, the brakes are hit more than 1,000 times, and the drivers are on the pedal nearly 35 percent of the time.
Brake fluid leaks and hot rotors equals fire!
This generates tremendous heat, and if you’ve ever watched a short track event on television, you’ve seen the undercar camera shots of disc rotors glowing cherry red. Those rotors are about 40 mm thick, and the pad linings start out approximately 32 mm thick. That’s each pad!
When the Car of Tomorrow (COT) first was introduced on these demanding tracks, it soon became obvious that the braking systems in use at the time couldn’t handle the new car’s needs. Because the new car design has the front spoiler so close to the ground, and airflow across the front is so different, insufficient air was getting to the braking components. That heat is going to go somewhere, and it did. It went into the front suspension components, wheel bearings and even the tires. Caliper piston seals were melting down, and even a newbie in the shop understands what that means: instant loss of pedal and an introduction to the wall.
PAGE 2Raybestos, the official brakes of NASCAR, was one company working to develop a solution. Before the 2009 season, Raybestos partnered with Joe Gibbs Racing and the British company Alcon. Alcon already was well known in international racing circles, noted for its experience in racing brake and clutch systems for Formula 1, IndyCar and others.
Using a system they call Optimized Structure Caliper Architecture, Alcon engineers were able to design calipers to meet specific needs and demands rather than take a one size fits all approach.
The method uses actual track data and software that incorporates Finite Element Analysis methodology to virtually test new designs before they are even made and tested on the track.
“The optimization process is all done using software,” says Phil Stubbs, president of Alcon, USA. “The whole process can be done on the screen and we manufacture the part using five-axis machining, which is the key to our ability to cut development time and improve the overall design.
“(Each caliper is) specifically tuned for each type of track,” he adds.
Integrating Requests
Meanwhile, Raybestos engineers are testing new friction materials in their own brake dyno labs. Using these machines, engineers can replicate the braking conditions incurred by the racecar at any track on the circuit. This reduces development time and cost, but final tests are performed on the track in partnership with NASCAR teams. Getting the pads to the teams is no problem either, with a dedicated facility and staff ready to fill the requests. Should a savvy crew chief want a little something special in his pads, or want them a little thicker or thinner than normal, the Raybestos staff can accommodate that as well.
Brembo is another supplier of braking systems to NASCAR teams, and also developed solutions for the braking problems suffered by the COT. All of its new calipers have internal body brake fluid passages, eliminating the wrap around lines that could be damaged by debris or from an over anxious tire change. Cooling is now integrated in the caliper, using a carbon fiber air duct that passes across the body. This duct also forces cooling air between the caliper pistons and the brake pads, limiting the migration of heat from the pads into the caliper. Caliper core temperatures are greatly reduced, helping to protect the internal seals and minimizing the risk of sudden fluid loss.
COT cars use more brakes than the old cars did, so more brake volume is required to make sure there still is some pad left by the end of the race. Brembo’s Intermediate track system married the old with the new, including a front six-piston monobloc caliper matched with four-piston monobloc rear calipers. The calipers use slightly larger pads for that added volume, in contact with lighter, yet stronger, rotors.
NASCAR fans enjoy watching their favorite drivers screaming down the front straight at Daytona or Talladega at speeds approaching the 200 mph mark. But the drivers and crew chiefs know that a race is often won or lost by the use of that middle pedal – the brake pedal – as much as it is by the pedal on the right.
