DRILLED AND SLOTTED VS. SLOT-ONLY ROTORS
When larger-diameter and thicker rotors were introduced to the car-buying public in the early 1980s via the C4 Corvette and some imports, street-compatible pad-formulation technology lagged.
As a result, pad outgassing (the pad boiling off the resins and binders used to hold the friction materials together) became a significant issue. You’ll know you have brake fade to pad overheating when the brake pedal stays hard, but the car won’t stop. If the pedal goes soft, you’ve boiled the fluid.
The answer was drilled rotors, which gave the gases a ventilation path. Slots allow the rotor to actively clean contaminants off the pad face, keeping the best elements of the friction material in use. As a result, drilled and slotted rotors—along with zinc plating to eliminate oxidization from the unscrubbed parts of the rotor—as introduced by
Baer Brakes in the 1990s became the default standard for high-performance brakes. You can see this today, as even the carbon-ceramic brakes on Ferraris and Corvettes are drilled. In the last five years, pad technology has evolved dramatically, and as a result, properly selected, high-quality pads don’t have outgassing issues. Instead, the additional heat generated can cause radial cracks at the drilled holes, especially with big-power, heavy drag cars or frequently used track-day cars. If the cracks are fingernail-width-thick or thicker, the rotor should be replaced. For these applications, slot-only rotors are recommended. For pure road-racing applications with no street driving, some racers will use a plain rotor with no zinc plating to speed up rotor seasoning and pad bedding. Talk to your brake provider’s tech support to get the right answer for your specific application.