Originally Posted by gangstadirty5

From the Mercedes-Benz new SLK brochure:

"At first glance, those little holes may not seem like much. But in a high-performance braking situation where rotors can get red-hot and brake fluid can boil, the ability to dissipate heat and vapors is vital. Rather than simply drilling holes in the discs- a method that can cause 'stress risers' that weaken the metal- the perforations in the SLK front brakes are cast in place to help maintain maximum strength."

Originally Posted by CKwik

None of my cross-drilled rotors on my previous car ever cracked. I went through 2 sets and tracked the car often. Not to say that cross-drilled rotors can not crack, but you have to look for specific features. Be weary of drilled rotors that have an abundance of holes. The advantage cross drilled rotors have over slotted rotors is that they allow pads to outgas when they overheat. When pads overheat, they start to vaporize and this creates a layer of gas trapped between the pad and the rotor. This is typically the first type of fade most drivers run into, evidenced by a stiff pedal, but necessitating more force on the pedal to get the car to stop as effectively. slotted rotors can do very little to vent air. If this is such a problem that you need to add a lot of cross-drilling, then you need to reevaluate your pads and the rotor mass. Make sure the holes are drilled between the vains of the rotor and not just randomly. This can prevent structural problems. Also look for spiral and offset drilling. They should be drilled so that they are not in a straight line from the center of the rotor. And if you were to trace a line along the arc of any of the holes, ever other set of holes should be along the same arc. Lastly, you want to make sure the holes are radiused. Cracking in any metal occurs at sharp points(corners). Radiusing the holes will reduce the chances of a crack starting at a hole in the the rotor's surface(where the heat is always highest).

My last car used Cross-drilled rotors sold by Stillen. They had all of these traits. It should be important to mention that it was a 240sx running on 300ZX brakes. Running large enough brakes are very important to any rotor. I would never use cross-drilling as a fix for any braking problem. Below is a photos of the rotors I used:

http://www.stillen.com/product_images/NIS3000_f.jpg

Notice there is only one hole per rotor vane and located between the vanes. The radius pattern for each set of holes alternate. Each hole is radiused. I would avoid rotors with a drill pattern like this:

http://neons.org/howtos/njne-kvr/show-kvr.jpg

It's more aking to perforation. Amazingly enough, I've seen a lot of porsche rotors with this type of pattern. It probably works out since porcshe tends to use rather large brakes on their cars so heat is less of an issue, but I find it pretty suspect myself.