Managing Brakes for the Road Course

Many car clubs have annual events that include track outings, both at the drag strip and on road courses. SHO owners benefit from an annual convention that also usually includes road course time for those who are interested. Many people consider the road course events the highlight of the meeting and often it is the first or only time that drivers get a chance to experience driving their cars at speed. These events are most enjoyable when they aren't cut short by foreseeable mechanical failures and this discussion is intended to help you avoid brake problems at the track, or, at least, to help you recognize problems before they become too serious.

To best understand how to set up and manage your brakes for the track, it is important to understand the physical function of the brakes. Brakes are energy converters. They stop your car by turning the kinetic energy of your moving car into heat energy. You may remember from high school or college physics that energy is never created or destroyed, it is just changed from one form into another. In order to stop your car the kinetic energy related to its motion has to be converted to another form of energy. Regenerative brakes in electric cars turn some of the kinetic energy back into electrical energy which typically gets stored in a battery or other electrical storage device. Without such an electrical conversion system, though, something else has to be used and converting kinetic energy into heat is straightforward with a friction system of some kind. In the case of the SHO there is a four-wheel disk brake system that relies on the friction between the brake pads and the iron rotors to generate heat from the kinetic energy. The number one problem in managing your brake system at the track is handling the heat generated from lap to lap.

So what is kinetic energy? Anything in motion has energy associated with the motion and this form of energy is called kinetic energy. It takes energy to get something moving, i.e., convert some sort of motive energy into kinetic energy, and when the object in motion stops the kinetic energy gets converted into some other form. The amount of kinetic energy stored in a moving object is described by

where E is the amount of kinetic energy in Joules, m is the mass of the object in kilograms, and v is the velocity of the object in meters per second. For example, a 3400 lb (1,542 kg) SHO moving at 100 mph (44.7 m/s) has (1542*44.7*44.7)/2 = 1540527.39 Joules of energy. To put that into perspective, if you wanted to dissipate all of that energy in one second you'd be dissipating 1.54 Megawatts of power in the form of brake heat. That's hot. That's REALLY hot. Since the kinetic energy is proportional to the square of the velocity, doubling the speed increases the energy by a factor of four. So the same 3400 lb SHO moving at 50 mph would only have (1542*22.352*22.352)/2 = 385201 Joules, which would be 385.201kW dissipated over one second.

That's a big difference in heat dissipating requirements between a 100 mph stop and a 50 mph stop. Typical braking events last longer than a second, especially if you're slowing down from highway speeds. Panic stops or emergency stops that do occur quickly don't occur often, so brakes for street cars are designed to handle the heat associated with one or two successive stops from a reasonable highway speed within a short period of time. A car on a road course may see applications of the brakes to slow from high speed several times per lap. If the heat continues to accumulate the brake component temperatures may climb above their designed operating temperatures. When brake pads or fluid overheat bad things start to happen and that's when a track event may become a lot less enjoyable or even dangerous.

So how do you manage the brakes to keep them from overheating? A simple model of heat accumulation in your braking system is a bucket with a small hole in the bottom. Applying the brakes adds heat, which is the equivalent of dumping water into the bucket. The amount of heat generated by braking from 100 mph to 50 mph is constant and that can be thought of as a certain amount of water. For illustration purposes only, let's imagine that that is equivalent to one gallon of water. Braking from 100 to 50 mph in one second adds one gallon to the bucket in one second, and braking more lightly to slow from 100 to 50 mph over two seconds just adds the same gallon of water to the bucket over two seconds rather than one. The hole in the bottom of the bucket represents the ability of the brakes to dissipate the heat. Again for illustration purposes let's say that the hole will drain one gallon from the bucket in ten seconds. Although the water goes out of the bucket more slowly than it goes in, as long as the water is allowed to drain before more is put in the bucket won't overflow. Adding water slowly, perhaps at a rate just above the rate of the leak, will prevent the water level from rising very quickly in the bucket. Waiting until it is drained completely lets you dump a lot of water in at once without overflowing it. The water level in the bucket will be the equivalent of the amount of heat in the brakes or the temperature of the brake components.

Heat management in the brakes can be conceptualized using the water-in-the-bucket model. If you brake hard frequently without allowing the brakes to cool, you'll be doing the equivalent of dumping a lot of water into the bucket without letting it drain back down. As the water level rises, so will the temperature of your brake components. If you brake more lightly over a longer period of time the brakes can dissipate some of the heat as they're braking which helps to keep the peak temperature (the water level in the bucket) from rising too much. Keeping the peak brake temperatures low helps to minimize the chance of heat related problems in the brakes. Being careful to not apply the brakes too hard too often will also allow the brake temperatures to fall as the brakes cool between pedal applications.

So there are really two primary ways to keep the temperature of your brakes from rising too much: driving technique and brake cooling. Driving technique can be used to control how much heat is generated (water dumped in the bucket) and brake cooling controls how fast the brakes can dissipate the heat (the size of the hole in the bottom of the bucket). We've already touched a little bit on techniques that can reduce the amount of heat put in the brakes by braking lighter and longer. We can also increase the size of the hole in the bottom of the bucket by cooling the brakes. We'll also talk about some simple things that you can do to increase the amount of heat that your brakes can handle which is like making the bucket bigger.

The brakes can dissipate more heat by providing supplemental cooling. European racing trucks often cool their brakes by spraying water on them, but that's a bit more sophisticated (and dangerous) than we need to get. Getting more air over the brakes also helps to keep them cool and this can be done by adding cooling ducts that direct ram air to the rotors or calipers. The more air directed over the brakes the better their ability to dissipate heat and the bigger the hole in the bottom of the bucket. Whether the air should be directed at the center of the rotor or the caliper depends on whether you expect the pads to fail before the brake fluid boils or not. On front wheel drive cars it is often difficult to get air directed to the rotor center anyway, and cooling the caliper can be very effective. Figure 1 shows an example ventilating duct installation on a SHO with an aftermarket brake kit. Short of installing ducts, just removing the fog lamps will increase the amount of air moving through the brakes. On Gen IIs this makes a noticable difference (note: it could be on Gen Is as well, I just don't have any experience with them). Removing the fog lamps is not difficult and they can be replaced after a track event. This is a simple, effective, no-cost mod that can help to keep your brakes effective at the track.

Figure 1. This is a SHO 12.5" Baer aftermarket brake with a cooling duct routed from the fog lamp opening. The duct deflects ram air toward the caliper and rotor area to provide supplemental cooling ventilation.

The stock SHO brake system uses iron calipers that retain heat once heated. Aftermarket "performance" brake systems often use aluminum calipers that not only weigh less but don't hold heat like iron calipers and respond well to supplemental air cooling. The iron calipers are good for street use where they can absorb a lot of heat associated with one or two panic stops, but this can work against you on the track.

As heat gets added to the brakes there are two components that are most likely to suffer from overheating first: the brake pads and the brake fluid. Brake fluid comes in all different kinds with many different wet and dry boiling points. On a road course we know that the brake temperatures can be expected to be much, much higher than what is encountered in typical street use, so we want a fluid in the system with a high boiling point. Brake fluids typically specify two boiling point conditions: wet and dry. Most brake fluids are hygroscopic which means that they absorb moisture from the air. In most street cars, including SHOs, the brake fluid can absorb water through the plastic reservoir. Brake fluid that has been in the car for very long has probably absorbed enough water so that the wet boiling point will represent the expected boiling point of the fluid. Most brake fluids have big differences between the dry (new fluid) and wet (water saturated fluid) temperatures. One way to keep the highest boiling point that we can for track use is to put fresh fluid in the system before a track event. There are many economic brake fluids with high dry boiling points but mediocre wet boiling points. One good economic example is Valvoline Synthetic fluid which has a dry boiling point around 500F, which is comparable to many racing fluids. The downside of this fluid is that it absorbs water quickly so it needs to be very fresh for track use.

It is very important to realize that the fluid that needs to be fresh and have a high boiling point is the fluid in the calipers, not the fluid in the reservoir. Just draining and filling the reservoir will do very little to improve the on-track performance of the fluid. Bleeding the brakes so that the fresh fluid gets into the calipers is critical for improving the performance. A reasonable reference for brake bleeding can be seen here on SHOtimes.

A good discussion on brake fluid properties can be reviewed here on the SHOtimes website. Although some of the technical data is dated the general discussion is very good. The ATE Super Blue and Amber fluids are still popular among racers and are available from several SHO vendors. The Ford heavy duty fluid is no longer sold in metal cans and may not be a good option for that reason.

The other brake component that is sensitive to temperature is the brake pad. Racing pads are made to have a very high coefficient of friction and the ability to handle very high temperatures. Many street pads are engineered to provide quiet operation, low dusting, and long life, with a lower coefficient of friction to extend the life of the rotor. Since street pads aren't expected to encounter the temperatures seen at the track, some may lose critical properties when overheated. Some pads used to be constructed with organic binders that would vaporize and turn to gas when overheated. The expansion of the gas generated under heat would create a pressurized region between the pad surface and the rotor surface that would effectively push the pad away from the rotor. This phenomena came to be known as "brake fade" because the brake performance would fade as the temperature of the pad increased. Fortunately, most contemporary pad compounds no longer do this so this sort of brake fade is a thing of the past. Modern street pads can still fail when overheated which may result in pad disintegration or a brake fire if the maximum temperatures are exceeded.

Racing or track pads can not only handle the high temperatures but they have a higher coefficient of friction than street pads. This helps you stop faster, but the result is that the bucket gets filled faster...the brakes will get hotter, faster, because they're stopping the car more quickly. This tradeoff has to be managed carefully at the track, since good brake performance helps by helping you stop quickly, but it heats the brakes while doing it, which is bad if overdone. The higher coefficient of friction also means that the wear on the rotor will be accelerated. This tradeoff can be managed to best suit your needs by careful selection of pads for the track and careful management of how the brakes are used on the track. A wide variety of brake pad compounds are available including pads engineered to provide a reasonable compromise between street and pad use. Plan ahead so that you can select pads that can meet your expectations for what you want to do. It isn't a bad idea to take an extra set of pads to the track with you in case they wear faster than you expect.

Some of the reputable SHO aftermarket vendors stock different pad compounds for street, track or combined use and keep the latest information available related to the pads. When changing pads and or rotors be careful so that the pads are bedded and the rotors surface loaded (seasoned) before going on the track. This can be accomplished by a week or two of street use or by using the bedding and seasoning procedures available on StopTech's website. StopTech has a lot of good technical data including bedding procedures available on their website here: http://www.stoptech.com/technical/.

So far we've covered the basics of heat management and things that we can do regarding the brake fluid and pads. There are other components in the brake system that can also be affected by heat, like the rubber dust boots around the caliper pistons. Under high temperatures these boots can disintegrate or burn away. The boots are there to keep dust and dirt out of the calipers and damaging them won't affect the short-term effectiveness of the brakes.

We've discussed some things about brake components, now we'll discuss a bit about actively managing brakes at the track. By now you understand how applying the brakes "fills the bucket" and you may not have much control over how fast the bucket drains. It is important to not overuse the brakes in such a way that the heat accumulation exceeds the ability of the brakes to dissipate that heat. The temptation at the track is often to go as fast as possible and then brake hard at the end of the straights. While this is a lot of fun it also puts the maximum amount of stress and heat generation on the brakes. While the SHO is not the heaviest sedan on the street, it is heavy for a track car and the brakes can accumulate heat quickly. Since there isn't a practical way to monitor the brake temperature from the driver's seat it is important to be able to recognize and respond to signs of changes in the behavior of the brakes while on the track.

Many times road course sessions are started with a few parade laps in order to allow the drivers to assess the track conditions, the condition of the car, and to warm up the car and driver for the session. This is a good time to get a feel for the braking zones on the track and how the brakes respond in each zone. The pedal should be high and hard and not require any pumping to build pressure in the system. The brake operation should be consistent and smooth. Having a feel for the response of the brakes when operating properly is key to detecting changes that may indicate an impending problem and this should be checked during the warm up laps. If during the event the pedal starts getting "long" or requiring more depression than normal to engage the brakes, this is an indication that something is changing in the system, most likely due to heat. If the pedal comes back up after repeated applications (i.e., pumping), then the fluid has boiled and released gas into the system. Overheating the fluid can also result in a soft or "spongey" pedal feel. Extreme wear of the pads may result in a long pedal that does not return to normal height with repeated applications. Any of these situations will only get worse with continued use and the degradation may be accelerated by continued overheating of the brakes.

If you begin to experience a soft or excessively long brake pedal, or need to pump the pedal up to get good braking, the best thing that you can do is slow down and safely exit the track to address the problem. Continuing to overheat the brakes when these symptoms appear may lead to further degradation or failure of the brakes. The good news is that if you do experience overheating symptoms it can be easily treated in the paddock in time for your next track session. If you come prepared with a spare set of pads, a good set of mechanic's work gloves, and spare fresh brake fluid, you can be back on the track in short order. Bleeding the brakes (usually just the front calipers) can be done in the paddock in a short amount of time and will restore fresh fluid to the calipers. If inspection of the pads reveals a problem there, it's not too much more work to change those, too, which can also be done in a short amount of time. Allowing the pads to wear down to the backing plates will damage the rotors, which are a bit more time consuming and expensive to change. If you do have to change pads or rotors at the track, be sure to take a short trip to bed the new pads before going on to the track, according to the procedures already cited on the stoptech website or elsewhere.

If you do manage your brakes well and you get through your track session successfully, take advantage of the cool-down lap to cool your brakes off before exiting the track. Use the brakes lightly and keep the car moving fast enough that the air removes heat from the brakes. If the brakes are left hot when you exit the track, the heat in the rotors and pads may soak into the caliper and boil the fluid while you're sipping coffee between sessions. When you get back in the car to return to the track it is always a good idea to check the pedal pressure before moving very far in the paddock to make sure that this hasn't happened. Light use of the brakes during the cool-down lap is usually very effective at removing enough heat to prevent this from happening.

Another thing to remember when returning to the paddock after a track session is that you should not apply the parking brake once you've stopped the car. Holding a hot pad in a fixed position against a hot rotor (like by applying the parking brake) can lead to pad "imprinting" which leaves a higher concentration of surface loading in the rotor under the pad than elsewhere on the rotor. This changes the coefficient of friction in the imprinted area with respect to the rest of the rotor and can subsequently be felt as a pulsating feeling under braking. This effect is often referred to as "warped rotors" and can also be caused by holding the brakes applied after a stop from high speed.

The disscussions that we've just been through apply mostly to the front brakes, but monitoring the rear brakes is always prudent as well. The rear brakes don't do as much work or suffer the same amount of stress as the fronts, since under braking much of the weight of the car transfers to the front wheels. The rear brakes are kept small to prevent the rear wheels from locking, and the weight transfer makes the front wheels the most efficient at stopping the car. This is why the front brakes are always larger than the rear brakes and do most of the work. SHO brakes are no different and the amount of work done by the rear brakes is much less than the fronts. If you do experience brake problems at the track it is much more likely that you'll have to address the front brakes than the rear. That being said, it is still prudent to make sure that the rear pads are in good shape and the rear calipers filled with fresh fluid when going to the track.

Track events are intended to be enjoyable experiences that provide a fun way for a driver to enjoy the capabilities of their car. They're also learning experiences that can be beneficial in understanding the limits of the car as well as your own limits as a driver. Brake failure during an event is not only dangerous but it also detracts substantially from the fun and experience that you could otherwise be getting from the missed track time. In order to maximize your track time and minimize the risk of brake failure, make certain that your brakes are adequately prepared before arriving at the track. Fresh brake fluid and suitable pads with plenty of friction material on them are critical. Inspect the rotors for cracks as well. With the brakes in good condition it is then up to you to manage them carefully during the event. It is a big secret among racers that braking hard and late is not only hard on your brakes, it also often results in longer lap times. Experienced racers can often obtain very short lap times with much less application of the brakes than novice racers. Braking early to save your brakes is not a wussy cop-out, it can actually be a smart thing to do for your lap times as well since it lets you accelerate for the next straight earlier in the corner. The bottom line is that it isn't necessary to overuse the brakes to get good performance out of the car and enjoy the event. Taking it easy and braking early allows you to find the limits of the car gradually while maintaining the integrity of the brakes.

When you go to the track have fun, take care of your equipment, and above all be safe.