In order to inspire confidence in your track day car with responsive brakes at every corner, an understanding of basic braking function and a few well-chosen modifications are all that are necessary. In fact, the ceramic eight-piston calipers that you’ve been dreaming about might not even be your best overall choice. All the track day brakes you need might be (mostly) on your car already.
Getting brakes to work properly on track is more about the integration of the parts involved than a giant rotors and multi-piston calipers. For most taking a street car to a track, the basic elements of proper brake fluid, brake pads, and rotors can be more than enough if they’re optimized to handle the demands of the event. To better understand how to properly set-up a braking system for track day use we’ve turned to the engineers at PFC Brakes.
Big, Heavy, Fast Cars. Tiny Little Rotors.
Though PFC offer brake pads, rotors and calipers for track cars, Porsche Cup racers, IndyCars, and just everything in between, their brakes used in Trans Am’s TA2 category caught our eyes for two reasons. As one of the most affordable professional road racing series out there, TA2 mandates reasonably-priced consumables, and the brakes are subject to plenty of cost constraints. In this department, calipers costs are capped at $550 each, and pads limited to $125 per pair. The iron-only rotors measure just 12.19″ in diameter in front and 11.75″ in the rear. The rotors diameters aren’t so different than the OEM set-up on many street cars.
Though TA2 cars rely on relatively small brakes, they are responsible for stopping a a vehicle that weighs nearly 3,000 lbs. with almost 500 horsepower. Despite these traits, the TA2 machines stop strongly and repeatedly. So, how does PFC do it?
To get their brake system to perform as needed, PFC went to lengths to ensure they achieved the correct levels of stiffness, heat dissipation, resilience, and efficiency for the application. First, the pad and rotor needed to meet certain deflection criteria to ensure even pad distribution as making the most out of the limited rotor surface area is a must.
A Hot Match.
With the amount of heat a TA2 car can generate when braking at the limit, it’s quite easy to get the rotors glowing red. Therefore, the goal is to minimize the differences in temperature across the surfaces of the pads and rotors. Since rapid heating and cooling means expansion and shrinking, PFC strove to engineer the entire assembly to heat-up as evenly as possible. “One of our main concerns is avoiding ‘hot spots,’ ” says Paul Rankin, Design Engineer at PFC. Otherwise heat differential can cause cracking of the rotors.
During a braking event, you want the force exerted by the pistons to be evenly spread across the friction face of the pad
“During a braking event, you want the force exerted by the pistons to be evenly spread across the friction face of the pad. This keeps temperatures consistent across the face of the pad as well as the face of the disc. By keeping consistent temperatures you reduce thermal stress, reduce thermal distortion, and reduce disc and pad cracking and failure,” he continues.
One of the ways to do this is by matching the rotor’s radial depth to the pad’s radial depth, so that no area on the rotor goes without contact with the pad. Rankin elaborates: “Let’s say, for example, that there is 10 mm of unused disc face below the inner diameter of the pad. You could say the radial depth of the disc is 10 mm greater than the radial depth of the pad. During race conditions, the portion of the disc that is in direct contact with the pad may experience temperatures in excess of 1300 degrees F, yet the 10 mm of unused disc will be many hundreds of degrees cooler. This large temperature gradient over a short distance causes a substantial thermal stress to occur in the disc,” he added. This stress can contribute to premature rotor failure.
Pro Tip: This is an area that any track day participant can explore with their stock braking system, either by matching the pads to their existing rotors or purchasing two-piece replacement rotors that better manage heat as well.
Remaining Stable in a Jarring Environment.
James Borner, PFC Design Engineer, explains that “the backing plate of the pad is being supported by the pistons and the tangential force on the face of the pads is located some distance away from the piston face. This creates a ‘moment’ that tries to pull the leading side of the pad into the face of the rotor. This causes the leading side of the pad to dig into the rotor and the trailing side to want to pull off the face of the disc. To counteract this, the trailing side of the caliper generally has a larger piston to exert more force on the trailing side of the pad to counteract the tendency for the back of the pad to lift off of the disc.”
To help stabilize the pad in the TA2 configuration, the calipers use offset bores, with trailing pistons larger than the leading pistons, which has the effect of stabilizing the pad. The front brakes use larger pistons than the rear brakes; the front pistons measure 41 and 44 mm, while the rear pistons measure 29 and 36.6 mm, respectively.
Pro Tip: For those running stock calipers on the track, the message is to make certain that the calipers on your car are operating smoothly without any hang ups or delays from one side to the other. In those cases the calipers need to be replaced or rebuilt.
What a Track Day Driver Can Learn From PFC's Experience with TA2 Brakes
Though TA2 might be more extreme than most novice or intermediate track addicts might be interested in, the wisdom used there still applies to the hobbyist with a less-than incredible brake setup. For those who have the chutzpah to challenge braking zones, they need to make the most out of their existing setup—minimal modification is what’s usually necessary.
Track-oriented pads and brake fluid come first. These two upgrades can be had for relatively little money and take a properly driven car to the end of each track session without an annoyingly spongy middle pedal. These modifications might provide more in terms of stamina, while competition-specific tires are able to increase overall braking force at the same time.
Still, threshold braking is requires confidence, strong technique, and a strong package. Eventually, even those with a more aggressive street/track pad and a confident, experienced driver can generate enough heat to run into issues. For those who push harder, “ducting might be a good intermediate stage,” adds Borner. When the heat spikes to a certain level, “Typical one-piece rotors have a tendency to morph into a cone-shape—upgraded two-piece rotor prevents this deformation, and also allow for some axial float,” he concludes.
Beyond that, the wisdom above can provide many ambitious drivers with that competitive edge they’re after. If the brakes and all ancillary components are understood, optimized, and treated with the appropriate combination of force and caution required, a driver once intimidated by the braking markers can smile confidently and sail many feet deeper than ever before.
Optimizing Temperature in Hellish Conditions
Though the TA2 pads can withstand 1472-1652 degrees F before performance starts heading south, to ensure strong braking performance PFC have implemented several features to keep the pads operating within their optimal range.
The tilted, directional vanes inside the rotors work like a centrifugal fan pressurizing the charge of air more than a conventional setup using straight vanes can, which necessitates left and right-hand side rotors.
On slower tracks or exceptionally hot tracks, even these vanes aren’t enough. Electric blower fans are employed to make sure the brakes remain cool when the natural airflow isn’t sufficient. Additionally, at exceptionally hot tracks, the ducts might be directed to cool the calipers as well as the rotors, to prevent the brake fluid from boiling.
Pro Tip: Track day cars can benefit from brake duct cooling. Often there’s an opportunity to remove a fog light or otherwise open up an area at the front of the car, like in a spoiler, for an air inlet. In many cases there are preformed brake duct covers available for popular track days cars, which direct cool incoming air to the right places.
Despite the small diameter required of TA2 brakes, with his PFC-setup John Atwell can run entire weekends without any issues whatsoever. After maximizing the cooling setup, he’s been able to run an entire weekend without loss of braking performance. Earlier this year at Sebring, Atwell started with a used set of pads for practice, and then replaced pads as well as the front rotors for qualifying.
Interestingly, Atwell doesn’t use a fan setup—even when running in serious heat. He found that, even in ambient temperatures of 90 degrees F, proper mounting of the twin-duct system was enough. “The first is set up to aim at the middle of the rotor; it blows through the center and then out of the vanes. The second duct is aimed at the rotor face for a little additional cooling,” he explained.
Be Mindful of not Over-Cooling The Brakes.
There is also such a thing as too much cooling. On a cold day a heavy stab of the brakes on a chilly rotor results in what is called “thermal shock,” and as the rotors are then subjected to a rapid climb in temperature, the rotors can quickly expand at a rate beyond what they’re capable of without cracking. This can also occur on a day with moderate temperatures at a track with long straights before heaving braking areas.
If that occurs, the ducting needs to be taped-off, altered, or even removed to reduce airflow and keep the rotors from cooling too much. It’s a tricky business finding that happy middle ground, but the mechanics in TA2 use a classic, time-tested technique to do it.
Because telemetry is strictly limited in TA2, teams use heat-sensitive paints on their rotors, which change color when they reach a pre-determined temperature. This helps the team determine the temperature each rotors is achieving. This also helps spotlight any differential in brake temperature across all four corners.
Pro Tip: This paint is fairly inexpensive and should be in the tool box of drivers participating in track day events.
Tuning to Achieve Full Deceleration Potential.
For TA2 PFC has developed four pad different pad compounds, each configured to accommodate different driving styles; some provide more initial attack, while others will ensure a smoother application.
Pro Tip: PFC offers up to seven different pad compounds for road racing. Talk with your PFC representative or dealer to determine which pads best meets your on-track needs.
Knowing how a brake will respond gives the driver true faith in their brakes; to predict the brakes’ response provides the driver with the confidence needed to push ten-tenths. “When the brakes are dialed in, the car hunkers down and just grabs the track,” Atwell adds enthusiastically.
If you end up dealing with low grip situations, you could send more bias towards the rear. Though this might seem counter-intuitive, it helps compensate for the loss in front traction
At the same time, even though the fluid must travel different distances to the front and rear axles. To ensure ideal “brake timing,” which is the rate at which fluid is sent to the respective calipers, the length of the pushrods in a TA2 car, or any car with dual racing master cylinders, can be adjusted to make sure the brakes trigger in the right order and at the correct speed.
For example, adjusting a slightly faster trigger of the rear brakes can help encourage a little rotation into a corner if desired. Essentially, getting the two axles to brake at roughly the same time, often with the rear just a hair behind, provides a safe and predictable car under deceleration.
For more information, regardless of whether you own a TA2 Camaro or a track-day NA Miata, please feel free to contact a PFC Technical Representative through the Source box below.