Friction is the force resisting the relative motion of elements sliding against each other. In the case of Cars and Trucks, it is the Brake Pads pushing against a Rotor, slowing the rotation of the Wheel and movement of the Car or Truck. The byproducts of this are heat and ‘Wheel dust’ as the Brake Pad material and Brake Rotor wear while doing their job.
Two Types of Friction
So friction is friction right? Not really. There are two types of friction when it comes to brakes.
Abrasive friction is the breaking of bonds of both the Brake Pad material and the cast iron of the Disc Rotor when the Caliper pushes them together. Abrasive friction is the wearing of the Brake Pad and Rotor to change forward motion into heat. Both components wear. Semi-metallic Brake Pads and some non-asbestos organics (NAO) use this type of friction.
Adherent (or adhesive) Brake Pad material forms a very thin transfer layer of Brake Pad material on the surface of the Brake Rotor. The two surfaces are the same materials and generate friction by breaking or shearing the bonds in the Brake Pad. Ceramic and some NAO pads use this type of friction. The transfer layer is bonded to the Brake Rotor’s surface and cannot be washed away by water or wheel cleaners. Adherent friction is easier on Brake Rotors because the Brake Pads become the primary wear component.
With both types of friction, it is critical for the Brake Rotor to have minimal runout. Abrasive friction materials will wear away at high spots, creating Disc thickness variation and Pulsation. Adhesive or adherent friction material could deposit the friction material unevenly and cause Brake Judder. If the Brake Rotors show signs of wear or unevenness, they need to be replaced for the new Brake Pads to operation correctly and quietly.
Friction Materials used in Automotive Brake Pads
How the components in the friction material shear, break and interact during Braking can determine a Brake Pad’s friction level, noise and wear characteristics. A Brake Pad may require up to 20 different raw materials. Some raw components of a friction material are abrasive, while other components lubricate. Some components, like structural fibers and resins, hold the Brake Pad together, while other components tune the friction levels through various temperature ranges.
Ceramic Brake Pads’ structural properties are very stable under high temperatures, much like CorningWare cookware, but that is where the comparison ends. Ceramic materials that go into a Brake Pad are very small strands that are engineered to be a certain length and width.
Since they were first used on a few original equipment applications in 1985, friction materials that contain Ceramic formulations have become recognized for their desirable blend of traits. These Brake Pads use Ceramic compounds and copper fibers in place of the Semi-Metallic Brake Pad's steel fibers. This allows the Ceramic Brake Pads to handle high Brake temperatures with less heat fade, provide faster recovery after the stop, and generate less dust and wear on both the Brake Pads and Brake Rotors. And from a comfort standpoint, Ceramic compounds provide much quieter Braking because the Ceramic compound helps dampen noise by generating a frequency beyond the human hearing range.
Another characteristic that makes Ceramic materials attractive is the absence of noticeable Dust. All Brake Pads produce dust as they wear. The ingredients in Ceramic compounds produce a light colored dust that is much less noticeable and less likely to stick to the Wheels. This could be an important factor if you have an expensive set of custom Wheels, or just want them to appear cleaner, longer.
Ceramic Brake Pads meet or exceed all original equipment standards for durability, Stopping distance and noise. According to durability tests, Ceramic compounds extend Brake life compared to most other Semi-Metallic and Organic materials and outlast other premium Brake Pad materials by a significant margin - with no sacrifice in noise control, Brake Pad life or Braking Performance. This is quite an improvement over Organic and Semi-Metallic Brake materials that typically sacrifice Brake Pad life to reduce noise, or vice versa.
Ceramic Brake Pads are available at a cost that is only a little higher than conventional premium Brake Pads.
Organic (Non Asbestos Organic, NAO) friction materials typically wear more than harder Semi-Metallic compounds. Generalizing about the wear characteristics of NAO and Ceramic-based compounds is difficult because there are so many variations. Wear varies depending on the formula the friction supplier chooses for a particular application. Most premium-quality Ceramic and Ceramic-based linings will provide long life and wear less than an equivalent set of NAO Brake Pads on the same application.
Semi-Metallic Brake Pads use metal fibers to give structure and provide friction. The metals used are typically high-quality steel, copper and other exotic metals.
The other part of the Semi-Metallic mix is comprised of a variety of materials like glues, lubricants and structural fibers.
Some friction manufacturers are picking and choosing the best properties of Ceramic, NAO and Semi-Metallic to make hybrid Brake Pads that are quiet, but still have aggressive performance. Some of these pads are problem-solvers for known noise-prone vehicles.
Our Brake Pad Replacement
At Benchmark Autoworks, we offer Ceramic Brake Pads almost exclusively. In our experience these offer the most satisfying Brake job both immediately in terms of stopping power and noise, and long term in terms of dusting and longevity. We also replace the Brake Hardware (some shops will cheapen out and avoid buying Brake Pads with new Brake Hardware), and fully grease the sliding surfaces. When considering having your Brake Pads Replacement, or general Brake Service, come see us at Benchmark Autoworks.
The above comparisons are general guidelines. The Brake Pad manufacturers offer a variety of formulations that can span the guidelines provided. Also, the descriptions are made with respect to street Vehicles, Cars and light Trucks, driven in consumer fashion on public roads. Race Cars, or Cars that are driven at high speed with periods of high acceleration and heavy Braking, use different formulations where wear resistance and noise are not important considerations. At Benchmark Autoworks we have experience also with Race Brake Pads for the weekend warrior, and can advise on those as well.