APPLICATION-SPECIFIC FRICTION MATERIALS CONTINUE TO EXPAND
Whether they say so or not, most of the major aftermarket brake suppliers today sell brake pads and shoes with friction materials that are formulated to match specific vehicle applications. In some cases, the friction materials in the aftermarket linings are the same or very similar to those in the OEM linings. In other cases, a different formula may be used — but it is typically a material that has been engineered for a specific vehicle platform or type of application rather than a broad spectrum "one-size-fits-all" friction material.
One leading brake supplier told us they now use about 40 different friction compounds in their various product lines to achieve application-specific coverage. Another supplier said they currently have 25 different compounds in their line, and will be adding more as needed to keep pace with new models and changes at the OE level.
Why so many different types of linings?
One obvious reason is that the braking needs of a Corvette are considerably different from those of a Kia. Likewise, the brakes on a Lincoln Navigator work a lot harder than those on a Cavalier (unless the kid who drives it is delivering pizzas).
The fact that asbestos is no loner used in new OEM brake linings is another reason why we have so many new application-specific friction materials today. In spite of its over-publicized health hazards (and the ongoing litigation that has spawned), asbestos was an excellent brake material. When brake manufacturers made the switch to non-asbestos organic (NAO) materials, they found it wasn’t so easy to replace asbestos with something else. They also discovered how hard it is to develop a single friction material formula that works well in every possible application from mini-cars to SUVs.
About the same time asbestos was phasing out, front-wheel drive was rolling in. The higher operating temperatures of the front brakes in most FWD cars and minivans required a material that could really take the heat. This lead to the development of various semi-metallic linings.
Then everybody started complaining about noise. Hard semi-metallic linings do tend to be noisy, so other new high temperature materials have been developed that contain ceramic fibers, aramid fibers, carbon, titanium, copper and numerous other "secret ingredients" that reduce noise and improve braking performance.
The widespread use of anti-lock brake systems has also played a role in the development of more application-specific brake materials. The threshold at which the wheels start to lock up depends on vehicle weight, speed, traction and the coefficient of friction of the brake linings themselves. Because the ABS control electronics are calibrated to the OEM brakes, aftermarket replacement linings should closely match the friction characteristics of the OEM linings — which, in most cases, requires the use of application-specific materials. That’s one reason why a growing number of aftermarket brake suppliers now "certify" that their linings perform at the same level of performance as the OEM linings they replace.
Speaking of performance, all OEM brake linings must meet government safety standards. The Department of Transportation standards require vehicles to stop within a certain distance, and the latest FMVSS135 rules require an even shorter stopping distance. Consequently, some OEMs have had to upgrade their brakes and go to more aggressive linings to meet these standards.
Yet there are no equivalent standards for aftermarket brake linings or any other aftermarket brake parts. The safest course of action for aftermarket brake supplies, therefore, is to use friction materials that are the same or closely match the OEM brakes — and to voluntarily certify their compliance.
The "J.D. Powers factor" is another driving force in the ongoing development of new brake pads and application-specific friction materials. Every vehicle manufacturer wants their cars and trucks to be ranked at the top of the latest J.D. Powers’ survey. A high ranking means more sales. To achieve higher customer satisfaction ratings, the OEMs are leaning on their suppliers to do everything they can to minimize noise, vibration and harshness (NVH) — which includes tweaking and fine-tuning the brakes.
Right now, all the major brake manufacturers seem to be fixated on the word QUIET. No squeaks, no squeals and no comebacks. The quieter, the better. That’s what everybody wants, right?
But achieving quiet hasn’t been easy. When a new friction compound is being developed, compromises often have to be made. The goal is to come up with a material that delivers quiet operation, has great stopping power and fade resistance, and delivers long pad life. But, the reality is you have to give up some benefits to improve others. Reducing noise often involves some degree of sacrifice in pad life.
As time goes on, we will continue to see the development of more and better application-specific friction materials from both OEM and aftermarket brake suppliers. We’re seeing more new classes of vehicles, such as "crossover" vehicles, that blur the distinction between cars and small SUVs. There’s also been a tremendous resurgence in street performance, with all kinds of hot new aftermarket brake products hitting the market such as slotted and cross-drilled rotors, high performance calipers and linings.
Right now the marketing guys who package and sell aftermarket brake linings are mostly emphasizing QUIET (and "ceramics") over other features of their products. But the fact remains; application-specific brake formulations are here to stay and will continue to expand with each new model year.