Friction and Fiction
“I would like a more aggressive or high-performance brake pad.” If you work at a typical shop you will hear this statement at least once a week. It is a complex request that requires a line of questioning to flush out what the customer wants, needs and expects.
“Aggressive”, “high performance” and “racing” can mean many things to the general public. It could mean a controlled stop at the end of a sweeping freeway off ramp, a series of hard stops on a twisty road, or some extra help while towing. But, for most people it means a more positive brake pedal that is not too soft and not too hard while encountering many driving conditions. You may be scratching your head to which one is right for the customer while wading through all the marketing jargon. But, the secret is to understand the customer before you try to understand the brake pad.
The first question should be: “What do you dislike or like about your current brakes?” A number of conditions can cause the customer to think the brake pads are to blame. The customer may have a problem with the master cylinder, calipers or other hydraulic components that could cause long stops or a sinking brake pedal.
Ask them when was the last time the brake pads were replaced. If they can’t remember, you might be better off recommending a set of premium pads that might return the brakes to “like-new” performance before they step up to a high-performance brake pad.
Ask the customer what they expect from an aggressive, high performance or racing brake pad. Their perception of what these pads can do for their vehicle may be 180 degrees from reality. Don’t worry about losing the sale, chances are the “up sell” has already been done for you by a magazine article, advertisement or product placement.
After you find out what they what, it is now the time to find out what they need. Ask about what kind of driving they do during the vehicle’s “normal” operation. Ask them if they carry heavy loads. Find out if they primarily drive on the freeway or twisty roads where the brakes are consistently being applied. The objective of these questions is to find out when, where and the frequency of critical brake applications. Creating a performance profile determines if the rotor and pad are cold during a critical stop, or if the brakes endure high temperatures for an extended period of time.
Now that you know what they need, you now have to move on to what they expect from their new set of brakes in terms of life, drivability and possible noise. This is insurance against miscommunication and possible comebacks.
Now that you hopefully have a clear picture of what the customer wants, needs and expects, it is time to source and recommend a replacement brake pad. This is the most difficult part of the process. Sometimes the customer may have a brand in mind because of a recommendation from a friend, a sticker on the side of race car or even Internet forums. In these cases, most of the burden is on the customer, but issue warnings accordingly. Most of the time the driver will leave it in your hands to select the pad.
When sourcing a set of high-performance brake pads, you have to sort out the marketing from the truth. The first thing to do is to leave all assumptions and generalizations at the door when it comes to these types of pads. Do not assume anything, and do your research, the manufacturers would not have it any other way.
What is High-Performance Friction Material?
In plain and simple terms, a friction material with a higher coefficient of friction or µ will use less pedal pressure to stop the vehicle. With lower pedal pressures, the driver’s right foot may be thinking, “These are really great brakes compared to my old friction material.” But, it goes much deeper than that when it comes to true high-performance brake pads.
High performance is an over used phrase in brake pad catalogs because it is both subjective and relative. The litmus test for most high-performance pads is if the friction material has the characteristics to meet or exceed the OEM specifications for coefficient of friction and/or temperature.
Under this definition, even some aftermarket premium brake pads that may not be labeled as high performance fall under the category of high-performance pads. This is because they offer a more stable friction materials that are formulated with the aftermarket age vehicle in mind.
The Total Package
A high-performance pad is more than some slapping a high µ or coefficient of friction material on to a backing plate. You have to look for the total package.
One defining characteristic of some high-performance pads is the backing plate. Backing plates can play a distinct role in creating a positive pedal feel and stopping ability. The backing plate creates a foundation for the friction material that must be stiff and stable. If a backing plate is flexing, the friction material is not in full contact with the rotor. This can cause longer stops, a softer brake pedal, and it increases the potential for unwanted noise.
High-performance backing plates might use thicker and better quality steel, but that is impossible to see. One visual clue is on the back of the pad. Look at the holes for integral molding (IM) on the backing plate. These holes might be in a different configuration than a conventional pad. With fewer or a different configuration of holes, the manufacturer can make a stiffer foundation for the friction material.
Some pads use backing plates without any holes. Without the IM holes, the backing plate is theoretically stiffer. These backing plates use mechanical attachment methods to attach the material to the pad. In some cases, the backing plate may use special surface treatments in conjunction with an adhesive to eliminate the IM holes.
Fade resistance is another feature of high performance pads. Brake fade can be caused by the out-gassing of the pad that creates a boundary layer of gasses between the pad and rotor. This happens when water, uncured resins and other components are heated to the point that they generate gases. The gases create a barrier between the pads a rotor that prevents friction from being generated.
Some manufacturers will try to minimize this from happening by heating or “scorching” the pads in ovens to cure the resins and remove moisture. This process can reduce the chances of brake fade, but it has benefits for the technician and driver. For the technician, the process can reduce bedding and burnishing time during the test drive. For the driver, it can eliminate the new brake pad smell that they might experience during the first few hard stops.
The high performance friction material market can be broken down into three segments. The categories can be looked at in terms of level of friction and temperature instead of drawing line between semi-metallic and NAOs. The field can be broken down into race, street-performance and high-quality/high-performance friction materials.
Race friction materials are the most aggressive. The edge codes for these materials might have the last two letters of gg, hh or higher. The coefficient of friction of these materials is around .4 to .55µ. These materials are typically semi-metallics.
When these pads are cold, they may be near impossible to deal with on the street because they do not reach the optimal operating temperature during normal driving. But, when they are warm, the braking performance of the vehicle is greatly increased. Also, these high µ friction materials have superior resistance to fade.
If customer insists on a set of these pads on their street vehicle, it is almost a necessity to install a brake bias adjuster valve for the rear brakes even if they install the same friction on all corners.
Noise? Some of these friction materials can produce a lot of noise when they are applied and even when they are not. But, they are made for racetracks and not the street.
These are pads for the weekend warrior. Typically these pads will have great cold torque and good high-temperature performance. These pads will not have the same overall coefficient of friction the racing brake pad, but at lower temperatures they will generate more brake torque and be more consistent as temperatures increase.
These pads are great for vehicles that may be taken to an autocross, track day or drag strip. There is no one material type for this category. Pads can be semi-metallics, non-asbestos organics (NAOs) or ceramics.
This category of pads include most premium pad lines from major manufacturers. Many of these lines are engineered to meet the needs niche applications and environments like severe-duty towing and fleet vehicles.
These friction materials closely mimic the friction characteristics of the OEM application. But, they typically improve on the OEM pad’s performance in critical temperature ranges and NVH performance. If a customer is looking to upgrade their performance from old brake pads, this could be their best choice.
Many aftermarket manufacturers have also gone out of there way to create lines and applications for popular light trucks, SUVs and fleet vehicles that can vastly improve on the OE’s friction formulation. These materials are formulated using aftermarket performance data that goes beyond the OEMs warranty time frame and intended operating conditions.
A brake pad is as only good as the rest of the brake system. If the system is compromised by worn rotors, leaking master cylinder or bad tires the high performance brake pads cannot work to their full potential.
Always try to sell high performance brake pads in complete sets for both the front and rear. Having a significant difference in the coefficient of friction between the front and rear can cause brake bias and vehicle stability problems.
High-performance rotors that are slotted or drilled can improve the performance of any brake pad. The slots and holes are designed to help redirect the boundary layer of gasses away from the pads. Also, the slots and holes create surface area to cool the rotor.
Braided stainless steel flexible brake lines are an upgrade that can give a more positive feeling brake pedal. These lines expand less under pressure when compared to OE flexible brake lines. This means that the hydraulic forces are used to push the caliper piston instead of pushing out the sides of a brake hose. These lines are available for a wide variety of vehicles and use the same installation procedures and mounting hardware as conventional brake lines.
Customer #1: “Freeway Phil”, Detroit, MI, 2004 Hummer H2
“I want a more aggressive pad that will bring me to a quick stop on the freeway or at the end of an off ramp. I drive about 30 miles to work on I-75. At the interchanges for M59, I-696 and I-94, it is not uncommon that I will go from 80 mph to 0 in a very short distance. There has even been occurrences when the ABS activates. I admit it, I like to drive fast and I like to have confidence in my vehicle. What do you recommend?”
Phil’s braking behavior is one where his brake pads and rotors must generate a lot of friction when they are cold. The three panic stops that Phil has to execute occur about 7 to 10 miles apart, so the brakes cool completely before the next panic stop.
One of the best choices for Phil is a NAO or ceramic-based friction material that has a lot of cold torque. These materials typically have a very flat friction curve when it comes to brake torque and temperature. This means that there is not much change in the level of friction from the start of the stop to the end.
Some manufacturers have made high-quality/high-performance semi-metallic and NAO pads specifically for Phil’s Hummer. These pads offer great performance in terms cold torque and higher temperature stops. Also, if Phil tows a boat or snowmobile trailer, these pads can offer extra confidence.
Customer #2: “Boat Anchor Bob”, 1998 Camaro, Atlanta, GA
“I drive my car to work everyday in stop-and-go traffic. On the weekends, I like to go to the drag strip and have attended several track days at Road Atlanta with my car club. I have had several incidents where my brake pedal has gone soft or dropped to the floor on the track. What do you recommend?”
Going with a full racing pad might be great at the track, but in Atlanta’s stop-and-go traffic it might be scary due to the lack of cold torque. In Bob’s case, a street high-performance pad will make a marked difference at the track. Also, Bob’s rotors may not last as long as he would like with racing pads.
Also, a set of braided stainless steel brake lines will help give him a firmer brake pedal, both on the street and at the track.