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Understanding the brake system and the terms used

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  • Understanding the brake system and the terms used

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    BILLET: To form a brake caliper from billet, a solid piece of cast or forged material alloy has excess material precisely removed under a multi-axis CNC machine until the desired shape is achieved. This process is used when intricate design details cannot be accomplished from the limitations of a standard forging process. Calipers made from billet can also be stronger than traditional press forged calipers depending on the material used.

    BRAKE TORQUE: Brake torque is essentially the power of the braking system. The brake caliper acts on the disc at a certain distance from the hub center, known as the effective radius. The force exerted by the caliper, multiplied by the effective radius of the system equals the brake torque. Increasing either the force applied by the caliper, or the effective radius results in increased brake torque.

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    AIR GAP: The area located between the rotor plates surface is airgap. The amount of airgap is a crucial factor in channeling airflow.

    ANNULUS: The area between two concentric circles. This dimension directly correlates to the friction surface area of the brake pad.

    UNSPRUNG WEIGHT: Unsprung weight in a vehicle is the weight of components that are below, or not supported by, the suspension of a vehicle; tires, wheels, brake assemblies, etc. This weight affects chassis dynamics and the handling of the car. High quality brake systems should have a good balance of low unsprung weight and high thermal capacity.

    THERMAL PROPERTIES: Thermal capacity, thermal expansion, thermal conductivity, and thermal stresses each define a material’s thermal properties. Depending on the brake system’s intended use and performance requirements, the materials used are selected based on their thermal properties. Iron for example is commonly used with brake discs for their high thermal capacity.

    THERMAL DISTORTION: Thermal distortion is the deflection/flex, or compressibility of a material under temperature and pressure. Both brake discs and calipers can flex and change shape when subject to excessive temperatures and pressures (load). This can result in the loss of feel in the brakes or flexing of the calipers, and eventually compromising the brake system abilities. Distortion can lead to several types of brake fade, excessive or unusual brake pad wear, unusual rotor wear, and damaged piston seals in the caliper.

    THERMAL CAPACITY: Thermal capacity, or heat storage capacity, is determined by how much weight or mass is located in the outer ring section of the disc. This is the area where the friction surface of the disc meets the internal vanes. The more mass located in this area, the more thermal capacity a disc has. Factors contributing to a disc's thermal capacity are: mass, annulus, disc width, air gap, vane design, and the disc material's thermal properties.
    Brake systems are designed to operate best within a prescribed temperature range. While modern high performance friction materials broaden this temperature range, it is critical that the brake disc in a system has adequate thermal capacity. Once the thermal capacity of a disc has been exceeded, the excess heat "spills over" to other braking components, resulting in loss of braking force (brake fade).

    OPTIMUM HEAT DISSIPATION: A brake system’s primary job is to store and release heat as efficiently as possible. The quality of materials, construction and design of a brake system dictate how effectively the system can manage heat. A brake system that cannot effectively dissipate this heat results in brake fade.

    It is a popular misconception that the slots or drillings in a disc determine the direction of rotation. In truth, for an internally vented disc, the geometry of the vanes dictates the direction of rotation. There are three vane types in use:

    1. Straight
    2. Pillar vane (comprised of many small posts)
    3. Curved vane

    The first two vane types are non-directional, and can be used on either side of the vehicle. The curved vane disc, however, is directional. A curved vane disc must be installed with the vanes running back from the inside to outside diameters in the direction of rotation. Orienting the disc in this manner creates a centrifugal pump. The rotation of the disc causes air to be pumped from the center of the disc, through the vanes, and out through the outside diameter of the disc. This greatly enhances the disc's ability to dissipate heat.
    Additionally, all of Brembo's slotted discs are directional as well, regardless of the vane geometry. The discs should be installed such that the end of the slot nearest the outer edge of the disc contacts the pad first.

    There are several reasons that a two-piece floating disc assembly is of benefit. First, by using an aluminum bell for the hub section of the disc saves a great deal of weight. Since this is both rotating and unsprung, it benefits the acceleration, braking, and handling of the vehicle. Secondly, it is better able to handle the large temperature changes that a brake disc experiences. In a two-piece floating disc assembly, the iron disc heats up uniformly, and the controlled float which is present allows for the differential expansion of the very hot brake disc, and the relatively cool aluminum bell. This allows the disc to be used under severe conditions without having a detrimental effect.

    At the speeds that stopping distance is generally measured from (60 to 70mph), the test is primarily testing the tire's grip on the pavement. As delivered from the manufacturer, nearly all vehicles are able to engage the ABS or lock the wheels at these speeds. Therefore, an increase in braking power will do nothing to stop the vehicle in a shorter distance. For this reason, we do not record stopping distances at this time. The Brembo systems will show their greatest advantages when braking from higher speeds, or when tasked with repeated heavy braking. The increased braking torque provides for maximum deceleration at speed, and the ability to absorb and quickly dissipate the intense heat generated during repeated braking insures that the braking system will perform at the same high level each time.

    Slotted discs offer increased durability under extreme conditions. They provide higher thermal capacity than a drilled rotor, which makes them a better setup in race like conditions. This is the more appropriate track setup as it constantly refreshes the pad and improves initial bite. You can also run more aggressive track oriented pads without the potential premature cracking seen with most holed discs. There are certain race pad materials that should not be used with a drilled disc.
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