Q: Why are some rotors drilled or slotted?
A: Rotors are drilled to reduce rotating weight, an issue near and dear to racers searching for ways to minimize unsprung weight. Drilling diminishes a rotor's durability and cooling capacity.

Slots or grooves in rotor faces are partly a carryover from the days of asbestos pads. Asbestos and other organic pads were prone to "glazing" and the slots tended to help "scrape or de-glaze" them. Drilling and slotting rotors has become popular in street applications for their pure aesthetic value. Wilwood has a large selection of drilled and slotted rotors for a wide range of applications.

Let's look at some common rotor "modification" and "performance" upgrades that you may have been exposed to. We'll try to separate the marketing from the engineering:

Bigger rotors will make your friends think you are cool, bigger rotors look ***y, but bigger rotors do not stop the car. What a bigger rotor will do is lower the overall operating temperature of the brakes - which is a GREAT idea IF your temperatures are causing problems with other parts of the braking system.

Take for example, a Formula 500 racer, a small 800-pound, single-seat formula car. While the brakes are certainly much smaller than those found on a 3200-pound GT1 Camaro, that does not necessarily mean that they need to be made larger. In fact, installing a GT1 brake package onto our formula car would probably do more harm than good. That's a lot of steel hanging on the wheel that needs to accelerate each time the gas pedal is pushed. So the moto of this story is bigger is better until your temperatures are under control. After that point, you are doing more harm than good, unless you really like the look. (And hey, some of us do.)

Crossdrilling your rotors might look neat, but what is it really doing for you? Well, unless your car is using brake pads from the 40's and 50's, 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." These gasses then formed a thin layer between the brake pad face and the rotor, acting as a lubricant and effectively lowering the coefficient of friction. The holes were implemented to give the gasses somewhere to go. It was an effective solution, but today's friction materials do not exhibit the same gassing out phenomenon as the early pads.

For this reason, the holes have carried over more as a design feature than a performance feature. 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 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, then these teams would be doing it.

The one glaring exception here is in the rare situation where rotors are so oversized that they need to be drilled like Swiss cheese. (Look at any performance motorcycle or lighter formula car. for an example.) While the issues of stress risers and brake pad wear are still present, drilling is used to reduce the mass of the parts in spite of these concerns. Remember that nothing comes for free. If these teams switched to non-drilled rotors, they would see lower operating temperatures and longer brake pad life, at the expense of higher weight. It's all about tradeoffs.

Slotting rotors, on the other hand, might be a consideration if your sanctioning body allows for it. Cutting thin slots accross 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 risks. (Have you looked at a NASCAR rotor lately?)

lets not forget those racers have special ducting to help cool the rotors, stainless steel brake lines and multiple pistion calipers.

truth be told, D/S rotors have less surface area. this means they will heat up quicker, espically with larger tires. we dont have the ducting to help cool them like a race car so they cant effectively transfer the heat.


Quote from (http://www.automotivearticles.com/Br...Practice.shtml)

So what cross drilled rotors do is reduce suface area decrease co-efficient of friction and are more prone to thermal shock, and cracking unless, you have a specialized braking system using, special brake fluid, stainless steel brake lines, venting all the necessary items to aid in convection