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Automotive

Understanding Today’s Performance Brake Components

Over the past decade, there has been an impressive intellectual property crime happening in the world of brakes. Instead of knocking off the latest movie, app or gadget, some Chinese companies have been creating caliper covers that make an ordinary single- or dual-piston floating caliper look like a six- or eight-piston racing caliper. While it is one of the most laughable modifications an owner can perform, it does demonstrate that there is demand for performance brake upgrades or at least brake components that have a high-performance appearance.

Is this an opportunity in the shop? Yes.

In my opinion, this passion for the appearance of the brake system can be a way to actually elevate the importance of brake system performance, while giving you a new sales opportunity, and a way to differentiate brake service offerings from other shops.

Knowing Your Customer

The first question to ask yourself and the customer is what does brake performance mean and how does it apply to their vehicle? A driver’s expectations can vary depending on their experience and how much propaganda they have absorbed. If you get to know the customer, you will find out if he or she is more concerned with appearance, performance, or both. This is not necessarily just for race cars or hot rods. For some customers, it might mean better brake performance while towing or enhancing a set of wheels.

There are three questions to ask a customer about what is most important from any brake system upgrade:

  1. “Are you experiencing any current issues with your brakes?” This question can help to address any problems with the current system like a low pedal or longer-than-normal braking distances.
  2. “What do you expect from the upgrade?” If the customer thinks a set of pads or rotors will instantly give their vehicle supercar-like brakes, they will be disappointed. This question is a chance to find out if they are looking for a stiffer brake pedal, decreased stopping distances or just a better-looking brake package.
  3. “How do you use the vehicle?” Drag, road and autocross racing each put different demands on the brake system and require different performance attributes. Even if the customer does not race, frequent stop and go traffic as well as frequent towing can make better brakes a valuable improvement.

What is Performance?

If you ask any engineer, you’ll find that it is tougher to engineer a brake system for the street than the track. On the track, the key is to stop – now. With street brakes, noise, efficiency and developing enough stopping force for specific situations dictated by federal standards must be considered.

The primary function of any brake system is to convert forward kinetic energy into heat energy using friction. How friction levels and heat are managed is what sets a high-performance brake system apart from a stock system.

When the OEMs are engineering a brake system, there are specific Federal Motor Vehicle Safety Standards (FMVSS) testing procedures for brake systems. The most demanding test for brakes involves a V-max test that consists of accelerating to a vehicle’s top speed (V-max) and stopping within a specified distance. The other stressful FMVSS requires performing ten successive stops from 30 mph. Both tests involve measuring the temperature of the brake pads.

High-performance “street” brake systems need to meet the same requirements and even exceed these test parameters.

Racing brake systems can vary due to the different types of racing environment. Drag racers need to perform a single stop from high speed with cold brakes. Circle track cars might have to make two stops a lap for 20 laps or more. Road racing cars might have to use the brakes 7-20 times during a lap.

These different performance requirements on both street and racing vehicles dictate the size of the rotor, caliper design, and formulation of the friction material. However, the limiting factor for all brakes are the tires. You could install rotors the size of garbage can lids and brake pads with the highest level of friction, but if the tires don’t have traction, the wheels will lock, causing the driver to lose control.

Almost every high-performance brake component improves the looks of the brakes on a vehicle. These cosmetic improvements are essential because late model cars and trucks are no longer using stamped steel wheels and the brakes can be seen through the spokes of the wheels.

Friction Materials

When NHRA Top Fuel classes switched to carbon fiber brakes in the early 2000s, there were several crashes attributed to the drivers not having experience with the new pads and rotors. Drivers were familiar with cast iron brakes and their ability to generate friction when the pedal was first applied.

Carbon fiber brakes reduced the rotating mass and were less susceptible to catastrophic failure due to heat shock. But, carbon fiber brakes did not start generating significant friction levels until they got hot. Many drivers panicked when they first applied the brakes and assumed it was a hydraulic failure and started to pump them rapidly in the shutdown area.

The same phenomenon can happen to street driven vehicles if the brake pads are replaced with a “race only” or overly aggressive friction material that needs heat to work. A lot of street performance pads can balance friction levels, meaning the driver is not caught off guard by cold brakes.

When most people think performance brakes, they automatically think semi-metallic brake pads. Semi-metallic friction materials use metal fibers to give structure and provide friction. The metals used are typically steel, copper, and other metals. Semi-met friction materials use the abrasive qualities of the metals in the pad and the rotor to generate friction. On an atomic level, the atoms and molecules of the pad and rotor are ripping their bond to create heat and friction of mechanical forces are applied. This phenomenon causes wear to the rotor and brake pad at different rates.

In some street applications, a performance pad with a non-asbestos organic or ceramic formulation might be the best choice for a customer’s daily driver where the cosmetic appearance of the brakes might be more important than late braking performance. These friction materials use adherent (adhesive) friction, in which the pad seasons or transfers a layer of material to the rotor. As the brakes are applied, the pads replenish the transfer layer. The layer can reduce rotor wear and even minimize brake dust if the driver is concerned about brake dust.

Rotors

A brake rotor absorbs and dissipates the heat energy generated by friction. How well the rotor can absorb and then release it into the surrounding air will determine the efficiency and capacity of the brakes.

The design of the rotor determines how it can handle the heat. On vented rotors, the thickness of the plates and how well air flows through the vanes helps to transfer heat to the surrounding air. Curved vane designs on some vented rotors help to pull air through the center of the rotor to the outer edge and act as a pump. For curved vanes to work, they must be mounted on the hub in the correct direction, just as a directional tire must be mounted on the right wheel.

Slots cut into the face of the rotor have two functions. First, they provide leading edges for a better initial bite from the pad. Second, each groove provides a path for the gases being released by the pad. If the slots fill up with pad material, the brakes system is operating at too high a temperature. Slots are radiused when milled to prevent stress in the rotor. Most slotted rotor manufacturers will not cut the slot to the edges of the rotor; doing so will compromise the strength of the rotor.

Holes drilled in the rotor can provide another path for the gases to escape from the pads and help with the initial bite of the pad. In some cases, the holes can reduce the weight of the rotor and improve cooling as well. But there is a science to the holes, so the structure or the rotor is not compromised. Too many holes or holes near vanes can cause cracks. Also, the hole should have a chamfer to avoid creating a stress riser that can cause a crack.

The size of the brake rotor determines the rotor’s ability to generate brake force or torque. The best analogy is to try to turn a steering wheel using an inner spoke and then again using the outer wheel portion. The further you move your hand out, the easier it is to turn the wheel.

Two-piece rotors included on some cars and in “big brake” kits have two advantages. First, two-piece rotors reduce rotational and unsprung mass. Second, the hat that is made of aluminum acts as a heat dam to prevent heat from being transferred to the hub, bearings, and knuckle.

The most significant trend in rotors is using slots, holes and finishes on the hat and vanes to improve the cosmetics of the brake system.

Calipers

For any brake pad to be 100% effective on the street or track, the caliper must be able to translate the hydraulic force evenly to the pads. To do this, the caliper must be able to float on the slides/brackets and/or the pistons must move freely in the bores.

Performance fixed calipers with four, six, or even eight pistons improve the braking performance by increasing the effective area of the brake pads. With more pistons, the hydraulic pressure from the master cylinder can be evenly distributed to the backing plate and friction material.

New calipers can also improve the cosmetics of the brake system. Many lines of premium brake calipers include high-quality coating, plating processes and finishes on the caliper, so it looks great behind the wheel.

Trends

Recently, we have seen a lot of companies entering the performance replacement market with kits that include drilled and/or slotted rotors packaged with brake pads for one or both axles. These kits are typically available online and rarely stocked by the traditional distribution chain.

Another option is to build your own brake kit. Many brake suppliers have lines of high-performance rotors and pads. You can pick and choose the right rotor and pad combination to suit the customer. For a customer that wants the appearance of a racing brake system but low maintenance, you can select a drilled and slotted rotor and then select a ceramic friction formulation to reduce noise and brake dust.

Some of these kits and components are the real deal and can improve not only the performance but the cosmetics of the brakes behind the wheels. Unfortunately, some kits are not – they’re really nothing more than the same old low-quality rotors and pads but with holes and slots in the rotor. Drilling and slotting a low-quality rotor will not change the metallurgy or configuration of the vanes. Do your homework.

Article courtesy Brake & Front End.

Categories
Automotive Featured

High-Performance Brake Jobs

high-performance-brakes
Brake jobs are a good source of parts and labor income for shops. When brakes wear out, most motorists just want you to fix the problem and restore their brakes to like-new condition with OE-equivalent replacement parts. But in some situations, there may be an opportunity to sell your customer on the benefits of upgrading certain brake components. We’re talking upgrades like:

Premium-grade pads that can handle higher brake temperatures without fading or wearing excessively.

Performance rotors that are slotted and/or drilled or dimpled to improve cooling and grip.

Multi-piston calipers to replace the stock floating calipers to increase swept area.

What type of customer is a likely prospect for brake upgrades? There are a few: those who tend to go through brakes rather quickly because of their driving habits; owners of sporty or performance import makes; and especially those who have already replaced their stock wheels with larger diameter aftermarket alloy wheels and low-profile tires.

Nothing looks worse than a set of stock rusty rotors and calipers behind a set of expensive alloy wheels.  The rear drum brakes on many imports are rather puny and certainly don’t do much to enhance a vehicle’s performance image. Converting the rear brakes from drums to discs is a major upgrade that improves both braking performance and appearance. The only mistake you want to avoid here is installing rotors that are too large for the rear brakes.

The larger the rotors, the more brake torque they can generate when the brakes are applied. Up front, that’s a good feature to have. But in the rear, too much brake torque can upset the vehicle’s brake bias and cause the rear brakes to feel grabby and lockup prematurely. The fix is to either use a properly sized rear rotor or to install an adjustable valve in the rear brake line(s) to reduce the pressure so the rear brakes don’t exert too much pressure when the brakes are applied.

ROTOR UPGRADES

Slotted and drilled or dimpled replacement rotors can be installed in place of the stock rotors without having to make any modifications whatsoever. Slots help sweep away the debris that forms on the surface of the pads as the pads wear. This improves their grip for better braking performance. Cross-drilled rotors or ones with dimples cast or machined into the surface allow the pads to breathe and help promote air circulation for better cooling.

A well-designed performance rotor may also have directional cooling fins between the rotor faces to help pump more air through the rotor. This helps the rotor dissipate heat so the pads don’t get too hot and start to fade when the brakes are working hard.

For highly modified cars, larger diameter rotors can provide more braking torque because of the “lever” effect. The larger the diameter of the rotor, and the farther out the pads are from the center of the rotor, the greater the braking leverage they can exert when the brakes are applied.

The limiting factor here is the inside diameter of the wheel. With stock diameter wheels, there’s usually no room inside the wheel to accommodate a larger rotor because the caliper would hit the wheel. But if a vehicle that originally had 14-inch or 15-inch wheels is fitted with 17-inch to 19-inch or larger aftermarket wheels, there’s usually a lot more room inside the wheels for larger brakes. A stock 10-inch rotor could probably be replaced with a larger 11-inch or even 12-inch rotor.

Another advantage of going to larger rotors is that larger rotors can handle larger pads. The greater the surface area of the pads, the more friction they can generate to stop the vehicle.

Larger rotors also help fill out the void behind large diameter, open-spoke-style aftermarket wheels. Some customers may not need the extra stopping power of larger rotors, but are more concerned about appearance and want larger rotors because of how they perform.

CALIPER UPGRADES

Replacing a set of calipers with remanufactured or new calipers certainly ups the total price of any brake job. Caliper replacement is usually necessary in high-mileage vehicles because of fluid leaks or because the calipers are sticking. But if a customer is serious about improving braking performance, replacing stock single-piston floating calipers with aftermarket multi-piston fixed calipers is the only way to go.

Most import and domestic vehicles come factory equipped with single-piston calipers. Why? Because they are adequate for normal braking and they are cheaper to manufacture than multi-piston calipers. Aftermarket performance brake kits typically include rotors with the same or larger diameter, multi-piston fixed calipers that replace the stock calipers, new performance pads (typically some type of semi-metallic or ceramic/metallic formula), new braided stainless steel front brake hoses and new caliper mounts (if required). Installation requires removing the original rotors, calipers and caliper mounts (if necessary depending on the size of the replacement rotors and the type of caliper).

Some of these kits can be rather pricey, depending on the brand name and whether the kit is designed for the street or for serious racing. A customer can spend several hundreds to thousands of dollars for such a kit. We did some price shopping online and found brake kits that ranged in price from $600 to $7,000 depending on the application.

Most of the aftermarket performance brake kits use fixed calipers rather than floating calipers. This is done so the calipers can squeeze the pads evenly from both sides. But this requires changing the caliper mounts and carefully aligning the calipers to the rotors when they are installed so that the pads wear evenly. If a fixed caliper is not perfectly parallel to its rotor, the front and rear edges of the pads will not wear evenly.

There are several reasons why most aftermarket performance brake kits use multi-piston calipers instead of single-piston calipers. One is to multiply brake force. The amount of clamping force the caliper applies to squeeze the pads against the rotor depends on the surface area of the caliper piston and the amount of force generated by the master cylinder. If hydraulic pressure from the master cylinder remains the same as before, then increasing the surface area of the piston by using more than one piston multiplies braking force.

The amount of clamping force generated by a caliper can be calculated as follows: First, calculate the surface area of the caliper piston. You can do this by multiplying the diameter of the caliper piston times itself, and then multiply by 0.785 to get the total surface area. Or, use the formula 2 x 3.14 (pi) x half the diameter of the piston (the radius).

Once you have the piston area, multiply that by the line pressure generated by the master cylinder that’s needed to lock up the brakes (typically 800 to 1,400 psi, depending on the weight of the vehicle, the brake system and tire traction).

Let’s say the stock brake system has single-piston calipers with 2-inch pistons, and the line pressure from the master cylinder is 800 psi. In this case, each caliper will generate 2,198 lbs. of clamping force at the rotors.

If you replace the stock single-piston calipers with dual-piston calipers, the pistons are smaller (1.5 inches), but there are now two pistons instead of one. So the clamping force is now the surface area of each piston times two, times the line pressure. Do the math and you’ll see that a dual-piston caliper with smaller pistons actually generates more clamping pressure at the rotor than a single-piston caliper with a much larger piston: 2,471 lbs. versus 2,198 lbs.

If you upgrade the brakes even more and install a set of four-piston calipers, the clamping force doubles again (four pistons now vs. two). The four-piston caliper with 1.5-inch pistons now has a total piston surface area of 7.06 square inches and generates a hefty 4,942 lbs. of clamping force with the same line pressure. That’s why race cars and true performance cars have multi-piston calipers.

Another reason for using multi-piston calipers is to reduce pad flex for better clamping effectiveness and braking friction. If a caliper has a single large piston and a relatively short pad, pad flex is usually not an issue. But if a caliper has longer pads (to increase the friction surface area), applying pressure only in the middle of the pad with a single piston may cause the ends of the pads to bow up slightly, with the most force being applied in the middle. So to ensure the full length of the pad contacts the rotor, two or more pistons are used to more evenly distribute the clamping force along the entire length of the pad.

To even out clamping force, some multi-piston performance calipers use different-sized pistons, typically smaller diameter pistons on the leading edge of the caliper, and larger pistons behind it.

Most aftermarket performance calipers are aluminum rather than cast iron and come powder-coated in a variety of bright colors. Some are also available with a clear anodized coating or are bright plated to help resist corrosion and enhance their appearance. Installing a set of brightly colored calipers will certainly dress up the appearance of any vehicle and enhance the look of the brakes behind open-spoke alloy wheels.

UPGRADING FRICTION MATERIALS

For street-driven performance cars, premium-grade pads are a must. Standard-grade pads are fine for everyday driving, and usually deliver OE-equivalent stopping performance, face resistance, pedal feel and wear characteristics. But for heavy-footed drivers or those who tend to eat brake pads, standard replacement pads may not be the best choice.

Premium pads are typically made with better materials. The backing plates may be plated to resist corrosion that can cause sticking and lining separation. The ingredients in the friction material are top of the line and provide the best combination of wear, fade resistance, pedal feel and noise control. Consequently, they cost more — sometimes a lot more, up to two or three times as much as standard pads. But for customers who want the best, upgrading to premium pads is often well worth the extra cost.

Notice we’re recommending “premium” pads, not racing pads. There is a difference. Racing pads are formulated for extreme temperatures and driving conditions. This usually means racing pads don’t perform well at normal braking temperatures on a street-driven vehicle. As stated earlier, racing pads don’t generate much friction until they get hot, which means increased pedal effort and increased stopping distance until they get hot. Noise and rotor wear may also be an issue with hard, high-metallic-content racing pads.

Another upgrade to consider is to replace OE-style pads with ceramic pads. Ceramic pads are a good upgrade for many passenger car applications. Ceramic pads are typically quieter than semi-metallic pads and generate much less dust than non-asbestos organic pads like those on many BMW, Mercedes and other European makes. Some aftermarket ceramic pads are specially formulated to duplicate the performance and feel of OEM “Euro” linings without the dust issues.

For serious performance, though, some type of premium-grade semi-metallic pads is usually best.

Courtesy Brake & Front End.