If you want to try endurance racing — a race more than six-hours long — you have to assess more than how much more fuel and tires you need. You should also consider other consumables — especially the brakes. With a thorough and honest assessment of what you have on your car now, you can ensure your race doesn’t prematurely come to a halt due to a lack of stopping power. We asked Darrick Dong, the director of motorsports at PFC Brakes, to offer his expert insight to help you go the distance.
Know Your Limitations
The rule book often restricts how much you can beef up your brake package. Keep it handy, as we discuss several aspects of your braking system to see if what you should do aligns with what you can do.
In addition to the rules, the wheel-and-tire combination determines how much you can modify the brake system. The larger the tire, the smaller the wheel, and/or the larger the amount of wheel backspace, the smaller the brake package you can run.
“The maximum package typically in a TCR car has a 35mm disc and two 25mm pads,” Dong says. “That’s an 85mm total stack of pads and discs. So, they may have to change the front brakes twice during a 24-hour period, depending on various factors.”
Despite small confines to work in, racers can get more brake material to work with. “[It may be a] 16mm pad, but it’s got 189mm worth of length into it,” Dong notes. “The pad volume is equivalent to a 25mm-thick pad.”
Front-Wheel Drive vs. Rear-Wheel Drive
Front-wheel-drive cars have more mass in the front — and with that comes an increased amount of load on your brakes.
“If you’re planning to go endurance racing with a front-wheel-drive car, then the challenge is how to present a brake package big enough to support not only stopping the car, but also the engine, and the gearbox,” Dong says. “Eighty- to 90-percent of the demand is on the front [with a front-wheel-drive car]. Whereas, with a rear-wheel-drive car, you’ll have between 60- and 70-percent of the demand on the front, which has a whole different set of parameters than a front-wheel-drive car.”
Some wheel designs can trap brake heat. Others help evacuate it. The key is to have a big enough air gap from the hot brake components and the wheel’s barrel. —Darrick Dong
The cooler the brakes, the longer they last. Adding a brushless fan and/or ductwork to your brakes increases their life. Dong recommends keeping the fans and hoses to the brake package as short as possible, with the least amount of bends to reduce stalling cool air.
Wheels play a role in cooling, too. “Some wheel designs can trap brake heat,” Dong emphasizes. “Others help evacuate it. The key is to have a big enough air gap from the hot brake components and the wheel’s barrel.”
Don’t Take Stock in Stock
The stock calipers may not be the best choice for a long-distance race. “Typically, a production car comes with a pin-slider caliper,” Dong says. “When the [OEM engineers] put the car together, they weren’t thinking about guys doing the 25 Hours of Thunderhill.”
A pin-slider caliper has pistons on only one side, and that side does most of the work. Meanwhile, the other side basically hangs out, all the while maintaining more contact with the disc than other types of calipers.
“A pin-slider caliper has more parasitic drag than an opposed caliper [with pistons on both sides] for the same amount of force,” says Dong. “That means the outboard pad tends to runs hotter than the inboard pad. With a pin-slider caliper, the maximum I’ve ever seen is about 17mm thick for the brake pad. Whereas with an opposed caliper, it’s not unusual to have 20mm to 25mm thick for the pad.”
Less brake pad volume results in less material to go through over the course of a race. Add to that, more wear to the outboard pad, and it results in a package that struggles with longevity.
If your car comes stock with drum brakes, Dong strongly recommends replacing them with discs. The complex drum brakes make monitoring wear and replacement more difficult and time-consuming. With more parts, more can also go wrong with a drum.
Ditch the Assistance
If your car comes with an anti-lock braking system (ABS), stability control, traction control, or torque vectoring — turn them off if the car permits. “Expect the wear to be 20- to 30-percent greater with ABS installed,” Dong exclaims. “These driver aids add drag to the brake system to reduce tire slip. Drag’s byproduct is heat. Heat affects wear.”
Don’t Forget the Back
Many racers focus on the front brakes, but you have four brakes for a reason.
“The rear of the car is just as important as the front,” says Dong. “The rear obviously needs balance and stability, but it also reduces demand on the front, to gain better performance and durability. For a front-wheel-drive, front-engine configuration, even that 10- to 15-percent rear brake becomes just as important to help balance the car.”
What Increases Braking Demand
With brakes, keep this physics principle in mind — force equals mass times acceleration (F = ma). Increase the mass or acceleration, and you increase the load on your brakes. Therefore, a heavier car taxes the brake system more than a lighter one.
Likewise, acceleration equals the rate of change in velocity over time (a=ΔV/ΔT). Simply put, the faster you go and the quicker you decelerate from that top speed, the more your brakes endure. So, if you race a track loaded with long straightaways and hairpin turns, you experience more brake wear.
Pit Stops for Brakes (Pros)
In long-distance racing, pit stops serve more than to refuel the car, put on fresh rubber, and replace the driver. You must add changing the brakes to that checklist.
“[Teams] have to figure out what is the millimeter-wear per lap or per hour [of brake pads],” says Dong. “What is the strategy [as far as when] to change the brakes? It’s no different than putting fuel or tires in the car.”
Your wear rate increases exponentially as the brake pads’ mass decreases. “Again, it’s no different than a tire,” Dong notes. “It goes 15 to 20 laps and doesn’t have much wear at all. Then, it starts to deteriorate rapidly. It’s the same thing as you lose mass in the brake pads.
“When doing calculations of [brake-pad] wear, you start off with what the brake pad does brand-new, and then you calculate what it does as it gets to 50-percent worn. [At that point] the wear rate goes up from when it was brand-new.”
To speed up pit stops — and reduce chances of component failures due to wear — professional teams install quick disconnects on the brake lines to swap out the entire corner’s brake assembly — disc, pad, and caliper.
“They change the whole corner so when they do the change, they have fresh brake fluid, seals, calipers, pads, and discs that have been bedded earlier in the session,” says Dong. “You have the least likelihood of having a seal failure because you ran the calipers too long or ran the pad too thin.”
Pit Stop For Brakes (Average Joes)
Ok, so the average racer probably can’t afford to change out the whole assembly as the pro teams can, but there are some things you can do make a pit stop for brakes smoother. Different manufacturers have different ways to change the pads, so make sure everyone is familiar with the race car. Have a plan in place before the race — even do some practice runs in the driveway. The more you practice the smoother it will go come game time!
And, first things first — it’s going to be HOT — make sure everyone has the proper equipment, especially gloves! Know who is going to be responsible for each step — write it on a whiteboard if necessary. Who makes sure the new pads are on the wall, ready to go? Who is on the jack? Who is on removing the tires? Who is on getting the old pads out? Who is responsible for pushing the pistons back in the caliper? Who puts the new pads in? How do you signal the rest of the crew if there is a problem, or even when your job is complete?
We turned to four-time NASA Honda Challenge Champion and regular-contributor to TURNology, Rob Krider, for some insight on how his Double Nickel Nine Motorsports team (www.team559.com) performed their pitstops to become the WERC Series E3 class champions in 2010. “For the 25 Hours of Thunderhill, we knew we wouldn’t be able to get through the long race without changing front pads,” Krider says. “The rears would make it, but the fronts would have to be changed at least once, maybe even twice if the drivers were super aggressive in the race.
“We didn’t have the budget to swap an entire brake assembly and use the quick change method on the brake line. Instead, we invested in some good welding gloves to protect our mechanic’s hands from heat. Then, we took a pair of large pliers and welded a couple of pieces of metal to the ends of each jaw that fit perfectly within our brake caliper to push the pistons back. We used the pliers in the opposite direction they were designed for — we opened them instead of closing them.
“The car came in, we jacked it up, yanked the wheels, unbolted the calipers, used our homemade tool to clear the pistons out of the way, slapped in some fresh pre-bedded pads, and bolted the whole thing back together again. The entire stop was less than four minutes. We would use that same stop to do other maintenance on the car and a driver swap.”
As you can see, planning for every scenario ahead of time will gain you valuable seconds, or even minutes, over those who aren’t prepared.
When racers go endurance racing, consumables, such as the brakes, factor in as the laps tick off. Luckily, with some preparation, brakes don’t have to spoil the marathon of fun racers can enjoy by going the distance. Upgrading to a premium brake pad such as those from PFC Brakes will help, but pads won’t do it alone.
Taking the time to assess your entire brake system before you enter the event will pay off for the long-haul. Knowing the demands on your equipment and taking into account the length of the race, will give you a better understanding of the strengths and weaknesses of your components and help you be better prepared to go the distance.