The Design of Brake Rotor Styles

  In addition to the standard solid face brake rotor design found on nearly all production vehicles, there are other types of rotors available, two of which have grown in popularity over the years. These include cross drilled and slotted, as well as a combination of the two, usually referred to as drilled and slotted. Cross drilled rotors became a part of the automotive lexicon in the 1960's after race teams and their drivers began experiencing a drastic decrease in their brake's performance after repeated hard stops. The problem was caused by brake pad gassing, which was common in organic and asbestos based pads. As the temperature of the pads increased, the bonding agents in the pads would break down, causing a layer of gas to form between the pads and the rotor. To solve the problem, holes were drilled in the rotor surface. Wilwood Disc Brakes explained the reasoning behind the practice, cross drilling provided an escape route for some of the burnt particulate and gases that were generated when the brakes were applied. This became known as degassing. The cross drilling process also provided a favorable byproduct of reduced rotating mass and unsprung weight. By removing some material from the brake rotors, it effectively lowered the weight of the race cars equipped with such rotors, giving them an even greater performance advantage over using standard solid face rotors. Similarly, adding shallow grooves, or slots, to the face of a brake rotor also proved to assist in degassing. In addition to degassing, the slots were determined to be effective at wiping debris from the pad surface and preventing a characteristic known as pad glazing, which can happen when brake pads are overheated leading to decreased braking ability. While beneficial to brake performance, slotted rotors didn't offer race cars the noticeable benefit of reduced weight.

   As with many technological advancements bred on the race track, both cross drilled and slotted rotors eventually made their way onto the street. This technology, which was born out of necessity, was introduced to vehicle owners as original equipment on many of the world's elite sports cars. This association with ultra high performance vehicles reserved a spot for these race bred brakes in the hearts of many performance enthusiasts, due in large part to successful marketing aimed at convincing consumers they need cross drilled brakes. But, just because they proved successful on the track and are standard equipment on the likes of Ferrari and Lamborghini doesn't mean they're the best option for street use. When it comes to selecting brake rotors for street use, the choices are typically more about style than performance. But, for track use, it's the never ending battle to find the lightest, lowest inertia parts capable of surviving the race. Making a good rotor decision requires understanding what the rotors really do.