Magazine for the auto service professional
Issue link: http://asp.epubxp.com/i/780462
32 | ASP February 2017 Technical 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 towards the rear of the vehicle. is 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 combina- tion 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 provid- ing 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. Rotor disc slots are often machined at an angle relative to the hub centerline, making the rotors directional (dedicated left or right). While some OE rotor manufacturers may specify that slots should sweep away from rotational direc- tion, in most cases, a slotted rotor (whether the slots are straight or curved) should be mounted so that the grooves sweep forward at the outer perimeter of the rotor, allowing the end of the slots closest to the outer disc edge to contact the pads first. In addition, some performance rotors feature a mixture of slot angles (forward angle, rearward angle and straight) as a design element. Unique slotting configurations are also offered, such as Raybestos' R-300 S-Groove slot 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. Some performance calipers will feature equal-diameter pistons, while others will feature pistons of progressively small-to-large piston diameters. When dealing with a caliper that features a staggered variation of piston diameter, the Raybestos' R-300 performance rotors feature an "S-Groove" slot design that simultaneously al- lows for out-gassing on both leading and trailing ends of the pad's swept area while maintaining maximum surface contact. The slot design is also non-directional, allowing the same rotor part number to be installed on both sides of the same axle. The high carbon rotor features a "black fu- sion" corrosion-preventative coating on the hat and a "grey fusion" corrosion-resistant coating on the disc, making them able to withstand 300 hours of saltwater exposure, the company says. Photo courtesy Raybestos