Quick Tech With Marlan Davis
We’ve previously discussed the possible pros and cons of cross-drilled brake rotors. The supposed upside of cross-drilling was preventing brake fade by improving gas venting of traditional disc brake pad compounds when they begin to break down at extreme temperatures, plus improved “bite” due to the numerous small holes improving the coefficient of friction. However, the big downside, particularly for long-term street use, was the possibility of microcrack formation that can result in catastrophic rotor failure.
Fortunately, there’s a way to obtain most of cross-drilling’s benefits without the danger of cracks: Slot the rotor face instead. Adding slots or grooves improves brake bite and ensures that as the pad friction material wears, debris particles are cleared away from the pad face and rotor. The slots may also help deglaze the pads.
Slots may be machined into the rotor either as a series of straight lines at an angle not perpendicular to the rotor radius, or as a series of curved lines. Grooves are directional; with the rotor mounted, they should sweep rearward at the rotor’s outer edge. The groove should not extend all the way to the disc face inner diameter.
Summit Racing [ This StopTech rotor fits the front driver-side on many 1999–2005 F-250/F-350 Ford trucks. Besides the slots, it also has a cryogenic treatment for greater strength during repeated heat cycling as well as resistance to internal oxidation and warping. Summit Racing sells it for $153.
TEN Archives [ Machining slots into the disc brake rotor face provides most of the benefits of cross-drilled brake rotors without the danger of cracking. As shown here, the slots should sweep toward the rear in the as-mounted position, and not extend all the way towards the disc’s inner edge.