Solid and vented rotors made with gray cast iron are the most common types of rotors. Drilled and slotted rotors are a variation of the same design. A vented rotor more commonly has a space between the two friction surfaces of the rotor. This helps with cooling and is more common on the front of the vehicle because the front brakes do most of the brake work. A solid rotor is just that – solid. There is no space between the two friction surfaces. Due to the brake-proportioning valve, the rear brakes only do about 20 to 30% of the braking and do not need to endure the same amount of heat that the front brakes do.
Stock replacement parts are normally solid faced rotors that are either vented or solid. Only performance vehicles (e.g. a Porsche) come from the factory with drilled rotors. When you buy a replacement part for your vehicle, there is some confusion as to whether you will receive a vented rotor or not. If your car came with a vented rotor, then the replacement part will be a vented rotor. If the car came with a solid rotor, the replacement part is a solid rotor. No solid rotor replacements are available for a vehicle that came originally equipped with a vented rotor.
Slotted and drilled rotors are a performance modification that do not increase braking power, but might aid in the cooling of the rotors in high heat situations. The down falls of having a slotted and/or drilled rotor might outweigh the benefits for many people depending on their braking needs. One rule of thumb is that if you are just daily driving, there is no reason to get a slotted or drilled rotor other than to improve the way your rotors look. The drilled rotors will provide more friction against your pads and reduce the life of them. When a drilled rotor approaches its service limit or possibly sooner, you might find that it has a crack from one or two if the outer most drilled holes to the edge of the rotor. These holes provide a source for stress cracks, so they would not be favored for racing. This happens because of the heating and cooling of the rotor in an uneven pattern because of the proximity towards the edge. The advantages are that the scrub friction of the holes and slots, while increasing the wear on your pad, reduce the chance that the pad becoming glazed.
The slotted and drilled rotors are clearly visible as the friction surface is not completely smooth. They have a series of slotted channels, drilled holes, or both. These rotors primary purpose is to reduce the effects of brake fade. Brake fade occurs when the rotor and pad reach a higher than recommended temperature. When the temperature is too hot for the pad and rotor to work properly together, brake fade occurs, which refers to the reduced feeling of brake power. The high temperature causes the brake pads and rotors to release a gas, thus reducing the friction that they would provide at lower temperatures. The slots and drilled holes are a means to dissipate this gas and reduce brake fade. The drilled rotors may even help cool the rotor; however, the drilled holes may encourage for temperature related fractures. When the hole closest to the edge of the rotor cools, it does this at varied rates which leads to a crack that usually forms from the edge of the hole to the edge of the rotor. Of course, when you are experiencing brake fade, you are punishing your rotors to the point that you could warp or crack a rotor regardless of whether or not it is slotted or drilled.