nottheone said:
I have to disagree with this. You will find that most cars have neither holes or slots in the rotors. You will see holes in rotors of high performance cars generally and they will be bigger rotors. They are there for cooling, gas dispersion and lightening, not for debris or water. If they were there for that all vehicles would have them. The higher performance the vehicle, the more likely it will be to undergo higher speed stops more often. One way performance cars are tested is with the 0 to 100 to 0 run. This tests both acceleration and braking.
Reviving an old thread to clear away some brake dust :)
Most road cars have plain rotors (no holes or slots) primarily for 3 reasons. First they are less expensive to manufacturer without holes and / or slots. Second, there is little or no benefit on a road car to offset cost. Thirdly, slots or holes reduce the useful life of the pads and rotors.
You see them on high performance and more expensive road cars for the look and to justify the higher replacement cost. Also, if the car is used for track days there is some benefit and if it is used in a one make or restrictive racing series requiring OEM brake disc there is great benefit, as explained below.
Drilled rotors have been used in racing because they are lighter but they typically crack prematurely as a result of having the holes an especially so on a heavier car or one using drilled brake rotors with marginal mass for the braking requirements. Porsche is one manufacturer who has used rotors with holes on racing cars but the rotors are well designed for the job.
Slotted rotors are what you see on the majority of professional racing cars that use iron rotors. Here are the reasons why they are used. All vehicle brakes, racing and highway, require an even transfer of the pad friction material onto the iron disc to work at their best. Racing friction, for the last 25+ years, has had a high metallic content making the transfer layer more important and in extreme racing conditions harder to control. Slots in the iron rotor greatly improve the quality of the transfer layer and also help keep extra debris cleared away. Pad wear is higher with the slots than without so clearing debris away is an important function.
"Pad gassing" and the need for holes or slots to deal with it is a non issue and especially so with today's metallic and semi metallic friction material. All pads and disc used in pro racing are pre burnished before they go on the car to insure a good transfer layer is in place. The process was innovated by and first introduced by a company in North Carolina, Pro-System, Inc. that also manufactures racing brake parts and tests friction material, discs and other brake components. That company has special dynamometers to properly test high performance and racing brake components.
Slotted rotors or drilled rotors may be better in water but it would be marginally so.
An added benefit to slotted rotors and to a much lesser degree drilled rotors is that they give better bite to the brakes, if that is desirable to the user.