Nearly everyone on this list has seen a cross-drilled rotor. They can be seen on most street-roaming exotica such as Porsches and Ferraris. They can be purchased from several aftermarket vendors found in Car and Driver, Motor Trend, Auto Week, etc. They are almost always on anything that is raced professionally, so they must be good for your street car, right?

WRONG.

('scuse me while I put on my Nomex undies...)

OK, wrong, maybe, application- and a whole lot of other things-dependent.

Here's the breakdown of "whole lot of other things-dependent". You be the judge.

Why are rotors cross-drilled?

Why do brakes fade?

What about grooving rotors?

Grooving rotors accomplishes much the same thing as cross-drilling; it's just not as efficient at allowing gas removal. Grooving also provides a slight scraping effect to the pad which can break a glaze buildup. Glazing is a hard, glass-like layer that forms on the surface of a brake pad that has gotten WAY too hot, molten actually. Needless to say, glazed brake pads have a rather poor coefficient of friction and should be replaced.

Something bears further explanation here: two characteristics that I've mentioned so far, pad outgassing and glazing, are normal characteristics of the older style, high-organic content brake pads, the kind with lots of asbestos in them, the kind that aren't generally available anymore. Why would anyone want to use a high-organic, asbestos brake pad when the new generation of metallic, carbon, and kevlar-based linings have higher coefficients of friction that are more consistant versus temperature, lower organic binder content, and substantially longer life than their asbestos counterparts? I'm not saying that the newer pad materials won't outgas and fade. They're far more resistant to this behaviour than the older materials because they are higher temperature materials to start with and they have much lower organic content. I won't go any further with this now, wait for Part 4: Sorting out the different brake pad materials.

OK, so you're still salivating over that cross-drilled rotor ad in the latest issue of Motorhead Fanatic magazine. Go ahead, order 'em. In fact, while you're at it, order several pairs; you're going to need some spares. These guys are just taking standard rotors and drilling them full of holes. The structure is weakened and the mass of the rotor is reduced, therefore limiting its ability to deal with heat buildup. I can almost guarantee that a set of these drilled rotors will be warped and dangerously cracked within 12 months, 2 or 3 months the way I drive. :-) (I road race my SHO, that's why I have the 13" Baer front brakes, with undrilled rotors.)

But Porsche and Ferrari do it!

Yep, and their rotors are designed at the casting stage to be cross-drilled. They have thicker rotor surface sections and more material in the cooling slots. They are stronger to begin with so they will hold together longer despite the cross-drilling.

Next time you're at the race track, get a garage or pit pass and spend some time talking to the mechanics. Ask them how often they replace the drilled rotors on their cars. The answer you're likely to hear is "every couple of races", assuming that they can afford it. Ask to see a used-up rotor. It will have radial cracks around nearly every hole. On holes near the outside edge of the rotor, the cracks may extend to the edge of the casting. Get more than a couple of these major edge cracks and the rotor is likely to self-destruct by throwing large hunks of itself at the insides of your wheels. Stopping is difficult when this happens...

At my last visit to the SHO Shop, I spied a pair of SHO front rotors that had been drilled. They were so badly cracked and heat checked that they would have shattered from a drop to the concrete floor. According to Vadim, they had been on a car for about a year.

Let's sum up the advantages and disadvantages:

For cross-drilling:

1. Better removal of gas buildup during brake fade.
2. Better cooling than a solid rotor, but only when force-cooled (brake ducts).
3. Looks cool.
4. Still looks cool when pieces of shattered, drilled rotor are embedded in your nice alloy wheels.

Against cross-drilling:

1. Shortens rotor useful life.
2. Drilled rotor will likely warp faster than a solid one.
3. Shortens brake pad life.
4. Only marginal improvement in fade resistance with modern brake pad materials.
5. Can result in catastrophic rotor failure.

OK, so you still want drilled rotors. ( I want to be locked in a closet with Gillian Anderson of the X-Files but that hasn't happened yet...) May I suggest the following:

1. Upgrade to larger rotors so they can take the heat buildup.
2. If you're into road racing, ditch your fog lamps (I have) and use the empty holes to start some 2" diameter silicone flex hose. Using great patience and a [lot] of cable ties, direct the duct along the subframe and onto the lower control arm so it discharges near the center of the rotor. You now have brake cooling ducts.

Let me say a bit about grooved rotors before I conclude. Grooving is not nearly as hard on the rotor's structural integrity as cross drilling. If you must do something visually appealing to your rotors, get them grooved. Grooving will accelerate brake pad wear, be prepared for this. Also, get in the habit of inspecting your rotors periodically, especially if they are drilled or slotted.

Or, get some brake pads with gas grooves in them. Gas grooved pads look like they have a saw kerf across their narrow dimension. Typically, the kerf depth is about 2/3rds the total depth of the friction material. Racers have been known to groove pads with a hacksaw blade, although I don't recommend that you try this at home; "standard disclaimer applies".