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5 Ways Temperature Helps Racing Experts Choose The Right Brake Pad
BY Front Street Media //
April 8, 2020
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Guest Author: John Butler, Lead of Product Development at Hawk Performance

Photography courtesy of Hawk Performance

Racing is brutal. It’s brutal on the car, it’s brutal on the equipment, and it’s brutal on you. But we love that brutality. It’s part of what attracts us to motorsports. We aim to push ourselves as far as we can as drivers, and we build the cars to be capable of being pushed to that limit. This is one of the reasons that race cars are built differently from street cars. The key to a proper race car is inherently found in the pieces that make it up, and of those pieces, one of the most critical is braking. 

100 percent of racers surveyed by Hawk Performance in early 2020 said that braking performance was a top priority in their race car. Not a single racer disagreed. So, what does that mean? Well, there are a few parts that go into a braking setup, all of which are important components to the equation—the caliper, the rotor, the fluid, the cooling. However, the most crucial part of the brake system is unequivocally the material that generates the friction to slow the car: the brake pad. With so many brake pad compounds available to us today, the topic of our discussion arises. 

Is it better to have a lower-friction pad operating well within your designated brake temperature heat ranges, or a high-friction pad barely inside the temperature operating window, and why?

I’ll give you a hint; when it comes to friction, everything is temperature-dependent. But to understand why that is, we need to understand what the brake pad is doing, and what we desire from its performance.

5 Ways Temperature Helps Racing Experts Choose The Right Brake Pad

How Do Brake Pads Work? 

The answer to what initially sounds like a redundant question may surprise you. Contrary to popular belief, a brake pad does not work by squeezing itself against a rotor. In fact, the brake pad squeezes itself against itself. During the ever-so-important bed-in process of a brake pad, the brake pad material transfers onto the face of the rotor as it wears. And it continues to do so with every push of the brake pedal. This creates a layer of brake pad material on the rotor that then offers a proper surface for the brake pad to generate friction with. These two surfaces are then forced together by the brake caliper, creating friction as that pressure increases. This friction is measured in something called mu, often shown as µ. That friction slows the car and generates an immense amount of energy, which is released in the form of heat. So, as we brake harder, we create more energy, which generates more heat. 

The tricky part is that the very friction material creating that heat is also directly affected by it. As we mentioned before, friction materials are extremely temperature-dependent, and the temperature that they are operating in not only affects the friction (or µ) they generate but also their behavior.

What Do We Want Out of a Racing Brake Pad? 

Braking in the motorsports world has never been as simple as stopping the car in the shortest range possible. It’d be a lot easier if it was! Instead, braking performance is the culmination of a variety of characteristics. The best racing drivers in the world find the limit of both their cars and themselves. For these limits, there are other characteristics in the braking performance that are just as important as its actual stopping capability. In fact, in that same recent survey of American amateur and professional racers, they ranked modulation, longevity, and fade resistance as the three most important factors behind outright stopping power.

5 Ways Temperature Helps Racing Experts Choose The Right Brake Pad

Stopping Power

This one is kind of a given, admittedly. Obviously, the later that we can brake into the turn, the faster we can go. Generally speaking, the stopping power of a brake pad is how much µ it will be creating at the temperature range in which it will operate. For example, a Hawk Performance DTC-80 brake pad is capable of generating nearly .7µ—double that of even the best street materials on the market. Triple the friction of the brakes on your average daily driver. More so, it will continue to generate that amount of friction even as temperatures climb above 1,700 degrees Fahrenheit. Because this DTC-80 material is designed to live in such an abusive environment, it needs that environment to function correctly. The DTC-80 will be at home in a 1,000 horsepower hill climb car with Hoosier tires that start with the number 3 and aero that will stick it to the ceiling. But no matter how fast you drive your Miata, you’ll likely never get a DTC-80 brake pad into its optimal temperature range. As we can see from the friction graph shown above, it will create more friction than any other material, and it will do so at as low of a temperature as 500 degrees Fahrenheit.

“But, of course, I can get my Miata brakes to 500 degrees Fahrenheit, so why would a DTC-80 not be my best choice?”

Because a material’s ideal operating range is different from its torque curve—it lies within the curve. And within that ideal operating range lies the below characteristics of which are just as important as outright friction.

5 Ways Temperature Helps Racing Experts Choose The Right Brake Pad

Modulation

Very rarely do we actually use 100 percent of our vehicle’s braking capabilities. Instead of a light switch, your brakes function as a dimmer switch. How bright that light gets is just as important as how easy it is to dim the light, and this is where the importance of an ideal temperature range truly comes into play. For example, the Hawk Performance DTC-60 is one of our most popular pads. The DTC-60 has an operating range of 400 to 1,600 degrees Fahrenheit. However, it’s optimal temperature range is actually 700 to 1100 degrees Fahrenheit. While the DTC-60 will stop the car incredibly effectively anywhere between 400 and 1,600 degrees Fahrenheit, the material itself is on its best behavior between that 700 and 1100 degrees Fahrenheit mark.

This means when within this temperature range, the material will create the most consistent results with the smoothest initialization and release. A brake pad that is now predictable, controllable with just the smallest movements in your big toe, and reactive to your input. A brake pad that you can use to pinpoint exactly how close you’re going to get to the car in front of you, precisely how late you’re going to brake, and specifically how and at what speed you will apply and release the brakes. This modulation—or feelis what gives us confidence in the car’s braking performance, along with the courage and the delicacy to dance on the edge of the limit of the car’s capabilities. This is what makes a brake pad fast because it gives the driver the tools they need to push harder throughout the entirety of the turn—not just the major deceleration areas. It’s important to acknowledge the distinction between the torque curve of a friction material and its optimal temperature range. Just because the pad is generating the friction to slow the car does not mean it is operating in its ideal temperature range.

Longevity

Let’s be honest, racing is expensive. Cars, in general, are expensive. In fact, anything with an engine is typically going to drain your wallet. Therefore, we naturally look to stretch every dollar we spend on our toys—and the longer those brakes last, the less they cost us in the long run. The lifespan of a brake pad is also hugely temperature-dependent, and as you may expect, overheating a brake pad does expedite its wear rate. But running a brake pad too cold also accelerates its wear rate. Rotor wear is also hugely dependent on the operating temperature of the brake pad. For example, most fully race-oriented pads—such as the Hawk DTC line—are very abrasive when cold. So not only will they wear themselves down faster, they’ll wear your rotors down more quickly as well. As they heat up and approach their operating temperature, they begin to behave better, and in turn, both pad and rotor wear approaches optimal rate.

5 Ways Temperature Helps Racing Experts Choose The Right Brake Pad

Just like modulation, brake pad longevity finds its peak right in the middle of the optimal temperature range. So a DTC-60 will find its best wear rate between 700 and 1,100 degrees Fahrenheit. The Hawk Blue, between 300 and 800 degrees Fahrenheit. And a DTC-80, between 1000 and 1500 degrees Fahrenheit.

Fade Resistance 

We’ve talked a lot about pushing the limit because that’s a lot of what racing—or high-performance driving in general—is. Spend enough time pushing that limit, and you’re bound to go too far. Our first line of defense when that happens is our brake system. As we’ve seen, brakes typically operate in a bell-curve relative to temperature. Brake fade is when we go too far, overheating our brakes and finding the end of that bell-curve and, thus, losing the brakes.

The graph below shows the average µ (or friction) that a Hawk DTC-60 creates across its operating temperature range. At Hawk Performance, our goal is to flatten that curve as much as possible. The flatter the curve, the broader the temperature range. The more extensive the temperature range, the easier it is to use across a more general application range. Friction materials will always inherently be based on a bell curve of friction relative to temperature. Blow this graph out, and we’d be able to identify the utmost limitations of the material. As a Hawk DTC-60 pad approaches 1,700 degrees Fahrenheit, it will begin to fade. At 2,000 degrees Fahrenheit, it’s struggling to stay alive.

While fade is scientifically inevitable, at Hawk Performance, we’ve put countless hours and dyno tests into ensuring that if that limit is reached and the material begins to fade, it does so slowly with consistency and predictability. Because the last thing anyone wants is to hit the middle pedal and have nothing happen.

5 Ways Temperature Helps Racing Experts Choose The Right Brake Pad

Ensuring that your brake pads have proper fade resistance is dependent on choosing the right brake pad manufacturer and ensuring the brake pad itself is operating within its optimal temperature range. If working within its optimal range, the brake pad will always have at least 500 degrees Fahrenheit of buffer room before brake fade becomes prevalent. Under-powering a brake system, or otherwise operating at the upper limits of a brake pad’s thermal range, means that brake fade can be just one wrong move away.

5 Ways Temperature Helps Racing Experts Choose The Right Brake Pad

Braking Environment

This brings us to our final point, which is the critical importance of understanding your braking environment. Do you know the range of temperatures in which your brakes typically operate? Most racers don’t. Brakes gain and release thermal energy exceptionally quickly, and gathering that data can prove to be difficult sometimes. This also means that using a thermal gun on your brakes after you pull off track is not always accurate, because the brakes can release hundreds of degrees of temperature just in the drive down pit-lane. Using a thermal gun can still be advantageous, but it’s crucial to understand the variance between real-world on-track temperatures, and what we are seeing long after the fact when we pull into the paddock.

There’s an abundant variety of expensive thermal tools you can use to measure live temperature ratings of your brakes. With proper—and expensive—instrumentation, the ability exists to measure thermal differences between the inner and outer edges of the rotor, peak points, low points, and other elements of the system. And that’s all great for an IMSA team with a seven-figure annual budget, but not very obtainable for the Miata in your garage. We recommend buying an easily affordable bottle of temperature-indicating brake paint. There are two types of temperature paint. Some indicate temperature by oxidation, and some by changing color. Temperature paint does not show you your average brake temperature, nor will it supply you with any detailed information. It will only help gauge your peak brake temperature, and that’s okay. On average, the typical car will operate mostly within a 400-degree-Fahrenheit temperature range, which peaks in the most substantial braking zone, and cools off in the straights. Armed with this knowledge, we can use our peak temperature to identify the thermal operating range of our own car and driver.

5 Ways Temperature Helps Racing Experts Choose The Right Brake Pad

Choosing the Right Brake Pad 

Choosing the right brake pad for you will always be a personal preference. Brakes are a vital part of any car, let alone a race car. The preferred behavior of its braking components is and always will be open to individual interpretation. That said, let’s boil this back down to our original question:

Is it better to have a lower-friction pad operating well within your designated brake temperature heat ranges, or a high-friction pad barely inside the temperature operating window, and why?

It is better to use a lower friction pad well within your designated brake temperature heat ranges. As we’ve discussed, not only is all-out friction capability only a fraction of what makes a brake pad ideal, but an appropriate temperature range directly affects all other aspects of a brake pad’s performance. A predictable brake pad that offers ideal modulation and fade resistance provides the driver the confidence to push harder, with the ability to use as much (or as little) of the brakes as possible. Choosing a brake pad that is operating on the outer edge of its operating range can result in a brake pad that may behave entirely differently in turn 10 than it did in 9 as it goes in and out of its thermal range. It will also wear exponentially faster, and often act as an on-off switch. This inconsistency stems from driver confidence, meaning the driver never even pushes hard enough to see the upper ranges of the friction capabilities. Often deferred as a poorly engineered brake pad, these symptoms usually mean one simple thing—you bought the wrong brake pad.

By using temperature-indicating paint applied to our brake rotor, we can identify the peak of our thermal range in our brakes and use that to identify what brake pads may work best for us. Let’s say you applied the temperature paint to your BMW E30’s brake rotors, and after a track day at Michelin Raceway Road Atlanta, that paint was brown. This tells us that our peak brake temperature is somewhere between 800 and 1,000 degrees Fahrenheit. Account for a generally accepted 400-degree thermal range on track, and we can make an educated guess at a thermal range of 500 to 900 degrees Fahrenheit. Using the operating range information available on HawkPerformance.com, we can decipher our options:

  • DTC-70 = 800°F – 1,200°F Optimal Range. Likely overkill.
  • DTC-60 = 700°F – 1,100°F Optimal Range. Close! Can work. 
  • HT-10 = 500°F – 1,100°F Optimal Range. Optimal Thermal Range. 
  • Blue = 350°F – 800°F Optimal Range. Potential to exceed the optimal range, but still within the acceptable range.

More importantly, what this shows us is that a DTC-80, which is optimal between 1,000 and 1,500 degrees Fahrenheit, or an HP Plus that is optimal between 300 and 600 degrees Fahrenheit, is not ideal for our application. We still have options for personal preference in feel and performance, but we are now assured that they are within our performance range. Many different compounds can work on many different cars, but understanding the thermal environment of your vehicle’s brake system can help you narrow down that list of options to what is appropriate for your unique vehicle and driving style.

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