Originally Posted by 1MOREMOD
what is the value of slotted vs cross drilled?
StopTech provides rotors slotted, drilled or plain. For most performance applications slotted is the preferred choice. Slotting helps wipe away debris from between the pad and rotor as well as increasing the "bite" characteristics of the pad. A drilled rotor provides the same type of benefit, but is more susceptible to cracking under severe usage. Many customers prefer the look of a drilled rotor and for street and occasional light duty track use they will work fine. For more severe applications, we recommend slotted rotors.
Crossdrilling your rotors might look neat, but what is it really doing for you? Well, unless your car is using brake pads from the '40s and 50s, not a whole lot. Rotors were first drilled because early brake pad materials gave off gasses when heated to racing temperatures, a process known as "gassing out." ...It was an effective solution, but today's friction materials do not exhibit the some gassing out phenomenon as the early pads. Contrary to popular belief, they don't lower temperatures. (In fact, by removing weight from the rotor, they can actually cause temperatures to increase a little.) These holes create stress risers that allow the rotor to crack sooner, and make a mess of brake pads--sort of like a cheese grater rubbing against them at every stop. Want more evidence? Look at NASCAR or F1. You would think that if drilling holes in the rotor was the hot ticket, these teams would be doing it...Slotting rotors, on the other hand, might be a consideration if your sanctioning body allows for it. Cutting thin slots across the face of the rotor can actually help to clean the face of the brake pads over time, helping to reduce the glazing often found during high-speed use which can lower the coefficient of friction. While there may still be a small concern over creating stress risers in the face of the rotor, if the slots are shallow and cut properly, the trade-off appears to be worth the risk. (Have you looked at a NASCAR rotor lately?)
And Zeckhausen Racing, a leading brake parts distributor:
Slotted rotors offer improved bite (initial onset of braking) and slightly higher friction level than smooth rotors. Slots prevent reduction in friction due to pad outgassing or brake dust trapped between pads and rotors. Pad coefficient of friction is maintained over the lifetime of the pads, since slots shave away glaze formation and expose fresh pad surface each time brakes are applied. Slotted rotors are by far the number one choice for cars used in competition or open track events. Best choice for heavy trucks and SUVs, particularly when extra bite is needed for towing. Disadvantages include slightly reduced pad life, some low frequency rumble and pedal flutter when braking hard from high speeds. If the slots are improperly machined all the way to the outside edges, then rotors may develop cracks sooner than plain or properly slotted rotors.
Drilled rotors offer slightly more bite and friction than slotted rotors. As with slotted rotors, pad coefficient of friction remains consistent over their lifetime. Wet bite is improved over plain and slotted rotors, so these may be the best choice for areas with heavy rainfall, like Seattle or Singapore. Weight is reduced by about 0.2 pounds per rotor, depending on size and drill pattern. Disadvantages include possible uneven rotor wear, typically concentric groove formation, although this is mostly an aesthetic concern. A major disadvantage is accelerated formation and spreading of cracks under racing conditions. For this reason, drilled rotors should be avoided for track cars, unless required by the rules.