For all that we ask them to do, disc brake pads don't get a lot of consideration, let alone respect. As long as they fit in the caliper and do a reasonable job of stopping the vehicle, a pad is a pad, right?
When it comes to high performance and racing, that common perception of brake pads is not only wrong, it can be downright dangerous. You can't throw a set of typical auto parts store pads on your high-powered street machine and expect them to hold up for any length of time. On a circle track or road race car, those pads can fail without warning, costing you a race or worse, your car.
Once you dig into the world of performance brake pads, you will find a bewildering array of compounds with different materials, wear ratings, friction values, and temperature ranges. Companies like EBC Brakes, Hawk Performance, Power Stop, and Wilwood make brake pads for very specific performance levels, both street and race. Even OE-replacement manufacturers like Bendix offer pads tailored for everything from Grandma's go-to-church-on Sunday sedan to high performance sports and musclecars.
In this article, we'll explain the basics of disc brake pad materials, how to choose a pad based on intended use, and the proper procedure for bedding in those new pads.
Brake Pad Materials
A disc brake pad is a simple thing, composed of a formed pad of friction material on a steel backing plate. The composition of the friction material is one part science and one part black art. Some pad manufacturers have more than 50 different compounds tailored for specific uses-and those compound formulas are more top secret than the alien spaceships the government says it doesn't have over in Area 51.
Back in the good old days, manufacturers used asbestos to bind the friction compound materials together. It resisted high temperatures, and the barblike composition of asbestos fibers held the friction material together quite well. When asbestos was phased out back in the early 1990s, pad makers went looking for a new material. The industry settled on three types-non-asbestos organic, semi-metallic, and ceramic. When you see a brake pad advertised as metallic or ceramic, for example, they're really talking about the binder that holds the friction material together.
Organic pads have a non-asbestos organic friction/binder material; the pads must have less than 20% metallic content to be labeled organic. The main benefits of a qaulity organic pads are quiet operation and longer rotor life. Because they are not as hard as semi-metallic pads, organic pads typically do not last as long and don't perform as well in high temperature applications like towing or racing. EBC Brakes Greenstuff 2000, Greenstuff 6000, and Greenstuff 7000 series pads are high-quality organic street formulations that offer stopping performance on-par with semi-metallic pads without the metal-to-metal confact and accompanying rotor wear.
Semi-metallic pads are made of a hard resin matrix with steel fibers added to increase hardness and prolong pad life. It's probably the most common pad available-most cars and light trucks on the road use semi-metallic pads. One big advantage of a metallic pad is improved high temperature performance; its grip actually increases as the pad warms up to operating temperature. That makes semi-metallics ideal for heavy- duty use (high performance street, towing, etc.) and racing, especially circle track and road racing. A downside to semi-metallics is noise-the pads' hardness and steel fibers increase metal-to-metal contact with the rotors, and tend to magnify noise-producing vibrations rather than dampen them.
Ceramic pads are the latest type on the disc brake scene. As the name implies, the friction material contains ceramic fibers as part of the binder. Ceramic is a good choice for the street because it offers stable, predictable friction characteristics, especially at lower temperatures. Ceramic pads also provide a consistent pedal feel that is unaffected by hot or cold (unlike semi-metallic pads, ceramic's coefficient of friction does not drop off as quickly when the temperature changes). Ceramic pads are quieter than semi-metallic and organic pads, and generate low amounts of light-colored brake dust so it isn't as noticeable on your wheels.
So which type of pad is the right one for your application? If you are looking for stock replacement pads on a street-driven vehicle, stick to the type specified by the factory. If your truck came with semi-metallic pads, for example, use semi-metallic replacement pads to maintain proper braking performance.
Fortunately, there is no problem upgrading to performance-oriented brake pads. You can safely switch from organics to semi-metallic or ceramic pads, or go from semi-metallic to ceramic and vice-versa. Upgrading your pads will help decrease stopping distances and improve pedal feel-and make you safer.
Here is a general guideline to help you choose the right type of pad:
• High-horsepower street cars
• Tow vehicles and heavy-duty hauling (passengers or cargo)
• Racing, especially circle track and road racing
• Severe-duty applications that generate high brake temperatures (hilly/mountainous terrain, city or other heavy stop/go driving, etc.)
• Daily-driven vehicles
• Performance-oriented, street-driven vehicles
• Applications where improved pedal feel, longer rotor life, and low noise/low dust are important
A rule of thumb: when shopping for pads, stick with proven brands. This is especially important when choosing pads for racing or towing, where brake failure can lead to disaster very quickly. Choosing a quality name brand is especially important when buying ceramic brake pads. There is currently no standard defining how much ceramic material a pad must have to qualify as a “true" ceramic. Some pads labeled as ceramic may contain very little of the stuff and will not perform as desired. High-quality brands may cost more, but you will get the performance you're paying for.
Choosing a brake pad for a race car is a more involved than choosing a pad for a street-driven vehicle. The pads must be able to function at the temperatures reached on the track; in other words, the brakes should not fade at operating temperatures. According to the folks at Wilwood, pad compounds rated for temperatures of 1,000 degrees Fahrenheit and up are usually necessary for most asphalt circle and road race applications. Dirt track, drag racing, and high-horsepower street performance applications can use pads rated at temperatures between 500 and 1,000 degrees Fahrenheit.
Keep in mind that these are general recommendations, not absolute values. Things like track length, brake cooling (airflow to the brakes), weather, and tire selection can affect brake temperatures. Like any other upgrade, the best way to find the right brake pad is run 'em at the track. You might have to go through a couple sets to find the pad that provides the best overall performance. Fortunately, Wilwood and other performance brake companies offer a wide range of pad formulations to help make your selection chores easier.
Bedding Your Pads
To ensure your new pads will work as advertised, they must be broken in, or bedded. Subjecting new pads to hard service right out of the box will result in poor performance or even damage to the pads and the rotors due to extreme temperature variations between the rotor surface and the body of the pad. Think of the bedding process are a "heat cure"; the new pads are gradually brought up to temperature and then slowly cooled over a period of time.
Here is a widely-accepted procedure for bedding brake pads for your street vehicle. It can be used with any pad type.
Step 1: Make 8 to 10 gentle stops from 30 miles per hour to 15 miles per hour. Allow 20 to 30 seconds between each stop so the brakes can cool down.
Step 2: Make 8 to 10 moderate stops from 45 miles per hour to 30 miles per hour. Again, allow a 20 to 30 second cooldown period between each stop.
Step 3: Make 8 to 10 hard stops from 55-65 miles per hour to 25 miles per hour, allowing 20 to 30 seconds of cooldown time between each stop.
Step 4: You should notice a more positive brake feel during the bedding process. If you notice any significant brake fade during the hard stop phase (Step 3), it may be an indication that the brakes are overheating. Immediately do some light driving without using the brakes to allow the brakes to cool down, then repeat Step 3.
Step 5: Drive at a moderate cruising speed, using the brakes as little as possible, until most of the heat has dissipated from the brakes. Avoid using the brake pedal to hold the car at any stops you make. Park the vehicle and allow the brakes to cool to ambient air temperature.
Alternative Bedding Procedures
Bedding Street Pads
Step 1: Drive smoothly and gently for the first 100 miles, avoiding harsh braking unless in an emergency. Try to do most of your driving in urban and stop/go situations. Freeway driving will not provide enough opportunities to use the brakes for proper bedding.
Step 2: From 100 to 200 miles, gradually increase the pressure when applying the brakes.
Step 3: After 200 miles, you can do the final bedding. Find a quiet, unused section of road. Get the vehicle up to 60 miles per hour, then apply the brakes and slow down to 10 miles per hour. Do this five times in a row. After the fifth slowdown, drive around slowly for a few minutes to allow the brakes to cool. Avoid coming to a complete stop while the brakes are still hot.
Step 4: Repeat Step 3 one more time after the brakes have totally cooled down. You may notice an odor from the warm brakes-this is normal. Once the final bedding procedure is done, it may take up to 1,500 miles for the pads to reach their full performance potential. Some noise is likely during the first 1,000 to 1,500 miles of use.
Bedding Race Pads
If you are using race pads on a dual use (street/race) vehicle, use the bedding procedure outlined above before going to the track. If this is not possible, use the following procedure to bed in the pads at the track:
Step 1: Make two laps around the track, steadily applying the brakes every few seconds. Make a cooldown lap, avoiding any unnecessary braking to allow the pads and rotors to cool down.
Step 2: Drive a third full lap and apply the brakes as in Step 1, but use slightly harder pressure each time. Make another cooldown lap. Do not park the car with hot brakes-try to let them cool as much as possible before coming to a stop.
Step 3: If you have excessive fade during competition after taking these steps, you must repeat the bedding procedure. Some brake fade early on is OK; this is called green fade and will eventually disappear (you will know this when the odor disappears). If you are getting fade after 20 laps and the pads are partly worn, try bleeding the brake system, altering your driving style, or trying another pad compound.
We hope this brake pad primer gives you a better idea on what types of disc brake pads are available, what each is best for, and how to break them in for optimum performance. Thanks for reading and happy stopping!