Brake Performance for Luxury Cars
Today’s high performance and “luxury” high performance vehicles are designed with elevated levels of engine, suspension, steering and braking performance, and command higher price tags as a result. Owners of these vehicles demand brake system service to match or exceed the OE design in terms of stopping power. Since these vehicles tend to be driven “enthusiastically” on occasion, the customer expects a firm pedal, high levels of stopping power and predictable, no-nonsense braking.
Attention to detail when servicing these vehicles is paramount. As engine power increases, accompanied by the potential for higher speed operation, there’s more demand on the brake system, requiring the system to meet these challenges. As a result, expensive luxury/high performance vehicles tend to take advantage of braking components that provide a higher level of performance. Rotors tend to be larger in diameter, and sometimes made of more exotic materials than are found on less expensive cars.
Brake calipers tend to emulate or duplicate those found on race cars, for superior stopping power under higher speed situations, providing a larger pad contact area and often utilizing fixed caliper designs that feature multiple opposing pistons.
After all, when the customer is paying big bucks for his or her new ride, they expect all of the latest bells and whistles.
Brake pad materials are routinely selected by OEMs to maximize braking performance. With regard to high-dollar luxury and high performance vehicles, customers expect superior braking capabilities, and the vehicle makers tend to utilize the best materials available, regardless of cost, in order to maintain maximum braking performance and to avoid issues of squeals, premature wear and/or brake dust accumulation on incredibly expensive alloy wheels.
When dealing with this demanding market, you simply cannot arbitrarily replace pads with whatever is readily available from a local supplier or at the lowest cost.
Pads intended for high performance European and some domestic vehicles likely use a semi-metallic or low-metallic material in order to generate a higher coefficient of friction.
Some ultra-exotic applications employ carbon/carbon rotors and pads or other unique application-specific pad compounding.Rotors
High performance vehicles (this may include both late model OEM vehicles that push the legal limits in terms of horsepower, torque, handling and braking, as well as custom vehicles built with these attributes) require high performance brakes. As part of the system, brake rotors must be able to withstand the rigors of performance use. In addition to potential rotor wear, issues of concern involve cooling channel rust.
Premium performance rotors may feature a high carbon content. Citing Centric Part’s offerings as an example, a proprietary blend of molybdenum and chromium is used in the casting process, which boosts braking power, reduces potential squeal, resists stress cracking under extreme braking use and aids in heat dissipation.
From an appearance standpoint, this formula also resists oxidation/rust, making the rotors look good for a longer period of time, as the increased chromium and carbon content is also more resistant to oxidation. Brake Parts Inc. reports its Raybestos R-300 high performance rotors represent another example of high-carbon metallurgy that improves cooling and vibration-cancelling.
Vented and solid rotors
Vaned/vented rotors are designed to release heat from the rotor. As the rotor rotates, the vanes pump cooler air from the center of the wheel, which carries this air through the vanes, picking up heat along the way and removing a percentage of that heat from the rotor. A rotor featuring straight vanes is bidirectional and may be installed on either the right or left side of the vehicle.
If the rotor features curved vanes, it is directional and must be positioned properly to achieve full heat-dissipation performance, mounted so that the vanes curve toward the rear of the vehicle. This causes hot air to be pumped from the center area outwards (pumping air from the inner diameter toward the outer diameter).Rotor drilling/slotting
An increasing number of high performance brake rotors feature disc slots, cross-drilled holes or a combination of both. While many enthusiasts are attracted to this feature from a visual perspective, these design elements serve a purpose. Both help to keep the pads clean by providing an escape path for pad residue as the pads wear, and to reduce the gas-ramping buildup between the pad and rotor emitted by pad material resins, reducing the potential “hydroplaning” effect as the pad pushes against the disc and aiding in keeping wheels clean by reducing pad dust buildup and improving brake pad “bite” for superior braking.
Slots or holes essentially serve the same purpose in terms of a self-cleaning attribute, with cross-drilled holes also aiding in heat release. If holes are featured, they should include a slight chamfer to reduce the chance of stress cracking. Unique slotting configurations are also offered, such as designs that are non-directional (non-axle-specific).Multi-piston calipers
Many high performance brake calipers will feature multiple pistons. As opposed to a single-piston caliper, this provides greater and more even distribution of pad application force along the length of the pad, reducing or eliminating the potential for tapered pad wear. When dealing with a caliper that features a staggered variation of piston diameter, the caliper must be mounted so that the smaller piston end is closer to the entrance or “attack” of the rotor, with the larger piston end toward the exit path of the rotor.
The smaller piston end creates the beginning of the clamping force and the larger piston end provides slightly greater clamping force, the combination of which helps to compensate for pad taper wear.A multi-piston caliper that features different-diameter pistons must be mounted so that the rotor travel path hits the smaller pistons end first. This means that the calipers must be dedicated for the right or left side of the axle.
This staggered piston diameter design also helps to alleviate any potential for pad resin gas “pressure ramping” effect.This pressure begins just after the point of attack as the pad meets the rotor, and continues to progressively build along the pad until it can escape at the exit end of the pad. Depending on the brake pad compound, as the pads compress onto the rotor, heat builds and resins in the pads react and gases are released to the pad surface, building a sudden “pressure ramp,” which forces the pads away from the rotor, which pushes the pistons back into their bores. ■