Before jumping into a monster-rotor full-tilt upgrade it is wise to remember that a deep pool awaits you. With four-digit prices tags lurking about this is a serious investment in a serious system of the car so you need to know the score before stepping to the plate. Beyond the usual intended usage, driving habits, street/circuit ratio and other criteria; an understanding of some basic tech surrounding the braking system is important. Things such as the effects of certain upgrades, misconceptions when it comes to big brakes, and definitions of key jargon are paramount to making an informed, proper decision without breaking the bank for a pumped-up set of stoppers. We enlisted the help of Carl Bush, Product Applications, Customer Field Service Specialist from Wilwood Disc Brakes to guide us through the highlights.
Q: What is the simplest, quickest way to improve braking performance? How does it improve performance?
A: Two of the easiest ways to improve brake performance can be from a pad and/or fluid upgrade. In the same way that a tire compound can have dramatic impact on traction, brake pad compounds can have a tremendous impact on stopping power, temperature range (fade resistance) and wear rates. Brake pad compounds can be formulated to provide higher friction values relative to their temperature operating range. The driver feels a measurable difference in deceleration; much the same way he would feel improved acceleration from a better tire compound.
Brake fluid is a little different. Brake fluid will not necessarily add stopping power, but it will keep the brakes operating over long sustained high-temperature runs by preventing pedal fade. Pedal fade occurs when the fluid boils from excessive heat and becomes aerated. This causes the fluid to become compressible and the pedal gets a very spongy feel. Good fluid will keep the pedal firm throughout the event. Running good quality race fluid and making sure the system is well bled with fresh fluid before the race is the best and usually cheapest insurance that there won't be pedal fade issues during the event.
Q: Explain the importance of, and compromises in, brake pad selection.
A: Brake pad compound selection is one of the most critical aspects of braking performance. For any race application, the concerns are stopping power (friction value), temperature range and wear rate The correct pad compound will be capable of generating enough friction to stop the car in conjunction the mechanical and hydraulic capacities of the vehicle. The compound must also be able to maintain those friction values within the temperatures that will be realized during the course of the event. Finally, the pad must possess adequate wear resistance to survive the length of the event.
Noise and dust are generally secondary considerations for all out competition. For street driving, or dual-purpose street/track vehicles, noise and dust become considerations and become compromises to overall stopping power and heat range. Pads heavily laden with metallic elements, in an effort to provide long wear and high friction in the upper temperature ranges, are often noisy, dusty and lacking in low temperature response.
A lack of low temperature response can be detrimental during highway driving or even in the staging zones of drag racing. Sometimes, it may not be possible to find one single compound that suits all driving conditions for one particular vehicle.
Q: What component system is under the most duress/abuse in a stock braking system and what does an upgrade do to the performance envelope of the system?
A: Pads, rotors, and fluid are usually the first items to fail when a stock system is subjected to heat from the rigors of competition. OE pads are a compromise between safe stopping distances in normal driving conditions and quiet operation for driver satisfaction. Pad fade is often the first failure when OE parts are put to the test. The car may still have a firm pedal feel, but the car isn't slowing down as well. Brake temperatures have gone past the effective temperature range of that particular compound. The fix is a performance or race pad compound with higher temperature range and hopefully an increased friction value.
Overheating of the pads, and the overall system for that fact, are often a result of the rotor weight and cooling capacity. One potential upgrade for an undersized rotor is increased cooling. Ducting cool air to a rotor can certainly improve cooling. Installing a heavier weight rotor or a rotor with more vanes or vane surface area will also help cooling.
OE grade fluid is marginal at best when it is new, let alone old fluid that has been previously heat cycled and allowed to deteriorate over time through moisture absorption. Having fresh fluid in the system before an event is essential. Using a premium grade fluid that is compatible with your system is often cheap insurance against pedal fade
Q: What are the most popular misconceptions regarding performance brake upgrades?
A: Most misconceptions involve the rotors. First, rotors can only increase stopping power if their diameter is increased. Installing bigger rotors also requires moving the caliper farther from axle or spindle centerline. This gives the caliper more leverage to stop the wheel.
Drilling, slotting, or any other machined surface treatments do not improve stopping power. They can have some effect on pad performance and longevity, but in of itself, the stopping power does not change.
There are cases where specialized coatings have been applied to rotor surfaces in order to use them with specialized friction materials for increased friction. But be wary of any sales pitch that offers increased stopping power from an iron rotor that has merely been modified by a surface-machining operation.
Second, many believe that drilling a rotor improves cooling. This is a catch-22. While the lighter mass of a drilled rotor may dissipate its retained heat faster than a heavier part, it also heats up faster and often to a higher critical temperature than a heavier part. And since cast iron does not like abrupt changes in temperature, many racers who have installed drilled rotors on high-temperature applications have experienced cracking.
The real purpose behind drilling a rotor is weight reduction where cooling capacity may not be an issue. If you're experiencing cooling issues, installing a drilled rotor may not be the answer unless the drilled part is overall heavier (more mass) than the un-drilled rotor you have removed.
Q: What are the advantages/disadvantages of multi-piece rotors versus one-piece units?
A: The only real disadvantage associated with two-piece rotors is that they generally cost more than a one-piece rotor. With a two-piece rotor, the hat portion is usually replacing a cast iron section with aluminum. This reduces weight.
The next advantage comes to rotor selection. Bolt-on rotors come in many configurations. This can give the racer or enthusiast options on rotor selection to match weight and cooling capacity, or appearance on any one given application. A two-piece hat assembly could give the option of running a lighter 32 vane rotor in the same place as a heavier 48 or even 72 vane rotor, without changing anything else in the brake system.
Another option with a two-piece rotor is the option for dynamic or "floating" mount rotors. Floating rotors can be very effective at eliminating stresses between the rotor and the mounting hat by isolating the difference in thermal expansion rates in two dissimilar materials. This can be very beneficial to durability in sustained high-heat conditions.
Q: What questions/considerations should one have prior to purchasing a brake upgrade?
A: First and foremost, you have to have a clear idea of what aspect of the brake performance you are hoping to improve. Do you merely need more stopping power? Do you need more stopping power at a different temperature range? Do you need more cooling capacity? If heat is not an issue, are you looking to reduce weight? Do you need to address premature pad or rotor wear issues? Do you need to adjust front to rear bias to optimize handling?
You may only be interested in a more custom look inside the wheel. If you're involved in sanctioned racing, are there rules that regulate brake upgrades?
Wheel size can also be a limiting factor. In addition to wheel size, compatibility with other components must also be considered. For example, consideration must be given to master cylinder output capability when considering caliper upgrades. Rotor size, weight, and configuration are also critical.
In addition to helping with the leverage that the caliper has over stopping the wheel, the rotor acts as the radiator for the brake system. It must be able to effectively absorb and dissipate the heat being generated, in any particular application, to effectively prevent the system from failing due to excessive heat.
Brake pad compounds must also be matched to the application for overall friction and stopping power, heat range, and wear rate.
It must always be remembered that the brake system is a system and that changes to any one component will most likely have an effect on another.
A: Swept area is the radial width where the brake pad is "sweeping" the rotor face. It is defined by the effective width of the pad, as opposed to the length of the pad.
Q: Are six-piston calipers better than four? Why? Are four better than two?
A: Piston count, and its effectiveness, is usually a function of caliper size and pad length. Increasing piston count does not necessarily increase overall stopping power. Hydraulic clamping force is a function of the combined effective area in square inches of the piston bores.
A caliper with four large pistons, or even a single, very large piston, could in reality generate more clamping force than a caliper with six smaller pistons. If a caliper with four pistons has the same effective piston bore area as a six-piston caliper, they will both generate the same amount of hydraulic clamping force.
The advantage of piston count has to do with pad length and how the clamping force is distributed over the length of the pad. Increasing piston count is more often a contributor to better pad wear and better consistency in pedal feel than overall stopping power.
Q: What is the value of upgraded brake lines?
A: Teflon lined, stainless-steel braided hoses will expand less under pressure than fabric reinforced rubber hoses. By eliminating line expansion, as well as compliance anywhere else in the system, the driver feels a more positive and firmer pedal response. Good pedal response can work wonders for driver confidence on corner entry.
Q: Do brake upgrades interfere with ABS operation?
A: Properly engineered, vehicle specific upgrades should be designed to work in conjunction with that vehicle's ABS system. If not, you may want to reconsider that particular upgrade. Upgrades that require disabling the ABS should not be considered for street purposes.
Upgrades such as calipers with the wrong piston area and mismatched volume requirements can affect pedal travel, mechanical advantage, and front to rear bias. All of these can contribute to adverse performance of the ABS. Choosing a kit or component that is ABS compatible is the best approach to avoiding potentially unsolvable problems and wasted money.