Glossary of Terms
“Balance bar or dual braking systems” refers to the brake pedal controls that use 2-master cylinders for separate hydraulic circuits for the front and rear but limited to that configuration. Their pressures can be adjusted with the use of a balance bar attached to the brake pedal. Most responsible racing sanctioning bodies require the use these controls as it offers redundancy for safety reasons. There are number of nuances with both their configurations as well as setting these systems up. See Balance Bar Setup.
“Bite” describes the response time or initial reaction the pad’s have when first engaged. This characteristic is designed into the PFC pads to maximize deceleration in the first ½ second of the stopping event while both aero and dynamic grip-traction of the racecar are at their optimum.
“Bobbins” refers to a generic term for the attachment systems used to couple a 2-piece disc designs with its mounting hats (or brake bells). There are as many bobbin designs as there is imagination.
“Boiled brake fluid” There are 2 types of brake fluids made today. Glycol-ester blends and high percentage ester content blends. Most popular is the glycol based. The glycol based fluids, normally has low compressibility but is “hygroscopic” which means it absorbs water. It is the water that gasses off and adds to the “spongy pedal” effect. This should not be confused with “brake fade”. The moment the fluid container is opened, it is absorbing water from the humidity in the air. When reviewing brake fluids, the contents label will list a dry and wet boiling point. The use of PFC caliper temperature stickers (Part # 032.0007) is highly recommended to monitor brake fluid and caliper seal condition. If the calipers exceed 210°C (430°F) for an extended period, the brake fluid and or caliper seals will deteriorate. High percentage ester blends have the promise of higher dry and wet boiling points. These type of brake fluids are usually more expensive than the glycol-ester blends. The reason is ester’s less water absorption qualities. But not all high ester blends are equal, and in many cases, although less water content to boil, compressibility may be an issue at elevated temperatures so spongy pedal effect is the same. PFC recommends Castrol SRF racing brake fluid because of decades of proven consistency and performance. Replacing brake fluid often and bleeding the brake system correctly is the cheapest insurance of consistent brake pedal.
“Brake drag” is the rolling drag that brakes incur at elevated temperatures. The goal of Performance Friction Corporation in its philosophy is to minimize this drag in the execution of all of our products. The drag not only slows the vehicle’s ability to accelerate, it reduces the ability for the brake pads to cool. It is the brake pads that are hottest component in the brake system. The drag greatly affects the pad’s ability to release and modulate as well. The key to minimizing this drag is PFC disc symmetry with all of the brake components to the interface area of the brake pads. No easy task because what is required to insure proper geometry at extreme temperatures.
“Brake Fade” is when the brake pedal is still firm but both the bite and the brake torque diminishes. There are many factors that influence fade, including excessive pad temperature, fluid temperature, vehicle traction degradation, and green effectiveness.
“Feel” is how dynamically, the bite, torque, pedal travel, and release interact with both the brake system components and the vehicle’s grip-traction level. This interaction, and the subsequent effects and their value are subject to debate from driver to driver. Certainly a moving target for all racing brake manufacturers.
“Fiddle brakes” this refers to a balance bar system that can not only control fore and aft brake bias but side to side brake bias. These systems are typically found in rally of off-road type race vehicles. Most sanctioning bodies have banned their use because of the electronic controls required to make these systems work. These systems should not be confused with modern ABS systems.
"Green Fade" occurs when either the pads or discs require an extended period of "bedding or burnishing" before they become effective. Green Fade is not an issue with PFC due to the Race Ready processing for it's brake pads and the machining procedures of it's discs. See our Pad and Disc Bedding for more information.
“Hard, Medium and Soft” brake pads, within the Performance Friction Carbon Metallic patented processes there is very little difference in the pad’s density. These terms come from earlier pad technologies where race tire terms were used to describe the pad’s characteristics. Today’s PFC pads have the different nuisances designed into them with very little change to the friction material’s density.
“Judder or brake shake” refers to the vibration the driver feel in either the brake pedal or steering wheel or both. In most cases it is caused by the increased thermal distortion of runout and thickness variation of the disc surfaces.
“Knock-back or Knock-off” This is when the brake pad has been forced away from the disc while the vehicle is in motion. The effect leads to soft or inconsistent initial pedal travel. If the driver taps the brake pedal and the brake pedal, improves, this is knock back. This can occur with both 2-piece and 1-piece design discs. There are a number of factors that influence this phenomenon. Drivers banging curbs is the leading cause. Too much or too little lateral float with the 2-piece design disc assemblies. Other areas of interest are - spindle; bearing hub deflection; the caliper’s mounting to disc concentricity at elevated temperatures; dynamic disc symmetry to the pads - to list a few.
“Knock-back springs” These are typically cone shaped springs that sit behind the caliper’s pistons. All proper race caliper designs have provisions designed into the caliper’s well area for these springs. The goal of the springs is to help stabilize the knock back. Excessive tension can lead to excessive brake drag and over heating.
“Mu” is the value of the coefficient of friction between the rubbing surfaces. Like tyres, many factors effect this value.
“Oxidation layer” refers to the pad material that has been oxidized by heat which causes discoloration. In PFC’s case, there is a patented graphite enhanced high temperature powder coating that reduces the effects of oxidation and will have a brownish tint to it. This can be a very good visual aid to determine if the brake pads have been over heated.
“Pedal Travel” is the amount of travel for a given force input or torque output.
“Prebedded or Dyno bedded or Dyno burnished” Although not required for PFC products, we offer prebedding to help minimize the perceived track time lost or to help isolate the driver’s influence. The pads and/or discs are dyno burnished in a controlled environment, with computer control plans in place to insure peak performance.
“Proportioning or prop valve” refers to a pressure limiting hydraulic valve usually inline with the rear circuit. Racing versions of these valves are typically adjustable. They can only bend or limit peak pressure, they can not add more pressure. Mechanical proportioning valves do not release pressure at the rate of pedal release, which causes poor modulation. PFC recommends the balance bar systems over the use of these valves due to inherent hysterisis, which affects release and modulation.
“Race Ready” a PFC trademark that refers to in it’s processing of brake pads regardless if they are race or street compounds. Essentially, the PFC brake pads are processed were by the “green effectiveness” is minimized and very little “bedding or burnishing” is required. New PFC pads may be used on new PFC discs with no issues. See our Pad and Disc Bedding for more information on bedding brakes.
“Recirculators or closed loop systems” refers to a hydraulic brake line system that has a series of check valves to insure fluid fill in one direction. The theory behind these systems is as the brake pads wear, a certain amount of fluid is displaced localized in the caliper’s well area. Although there may be some benefits initially with providing a promise of a firmer brake pedal, the subsequent added brake drag due to the hysterisis of the inline check valves affects release, modulation and reduces the ability for the brake pads too cool. PFC highly discourages the use of these products. These systems should not be confused with “bump cycles” strategies used in modern ABS systems.
“Release” or modulation, is the ability to control the release or time response of the decrease in braking power to prevent overwhelming the available mechanical grip of the tire’s traction with the track surface allowing the driver to optimize tire adhesion without locking wheels. This is where PFC stands out from other manufacturers, in that our superior release characteristics give the driver unrivaled control with the highest torque. Release characteristics are ultimately important in technical corners and high speed finesse braking.
“Seal pull back, seal roll back” The symptoms are the same as knock-back. The pistons in the calipers are being pulled back due to seal geometry. There are many factors that effect how the seals interact with the piston surface. Seal design, seal tension, seal groove shape, seal condition, and bore distortion are just a few areas of interest.
“Soft or long pedal” Dynamically, there are number of reasons for the brake pedal to be soft initially or go soft while the car is in motion. If initially, the area of interest is the bleeding procedures especially when a dual master cylinders when a balance bar is used. If a new brake system is installed, then ensuring the correct size master cylinder(s) is used. If the brake pedal is firm initially, but drops or pumping the brakes is needed to firm up the brake pedal feel then refer to brake fluid, knock-back, judder sections as all will affect the brake pedal consistency.
“Torque” is the amount of decel during the braking event for the given amount of driver effort. An important area of improvement for PFC is how smooth the torque delivery is for the given driver’s input.
“Transfer layer” is the layer of friction material that is transferred to the disc’s wear surface.
“Warped rotors” Although the effects are similar to brake vibration, the leading cause is the brakes have been over-heated and leaves the discs warped. Once the discs have been warped, it is seldom that they can be refinished successfully. It is highly recommended that you refer to our proper bedding procedures as well as the use of temperature sensitive paints to monitor dynamic disc temperatures. |
