Question about cross drilled and slotted rotors.

[Cerwin Vega Fan]

Ok my friends are telling me that their aftermarket cross drilled and slotted rotors give them better stopping power. For some reason that sounds wrong to me. I could see how the rotors would get rid of heat quicker but cross drilled/slotted rotors have less metal for the pad to grip. Which in turn should equal less braking power, or if not less then certainly their would no gain in stopping power. Could someone help clear this up for me and let me know am I right or wrong?

Thanks

[TraceZ]

Ok my friends are telling me that their aftermarket cross drilled and slotted rotors give them better stopping power. For some reason that sounds wrong to me. I could see how the rotors would get rid of heat quicker but cross drilled/slotted rotors have less metal for the pad to grip. Which in turn should equal less braking power, or if not less then certainly their would no gain in stopping power. Could someone help clear this up for me and let me know am I right or wrong?

Thanks

The slots and holes provide extra surface area for cooling. The biggest problem wiht brakes is fading, which is caused by heat. The problem with drilled rotors is they often crack between the holes. It is better to get just slotted ones.

[Z Ya Later]

I've been looking at upgrading the brakes on the Z. But, from what I've read...don't slotted rotors also chew up the pads quicker? Or is this just a myth. Thanks.

[Joe 1320]

On a hard stop, superheated gasses and pad material begin to build up between the pad and the rotor surface. This causes a reduction of braking power. The slots or holes help give this material someplace to go and away vent them from the pad / rotor contact surface, they help cool the surface and help restore braking in performance situations.

Not only that, these rotors are often thicker with extra cooling fins on it's circumferance for additional resistance to warpage and heat soak.

There have been some lower quality cross drilled rotors that have been known to crack between the venting holes, the good stuff lasts though. There are several variations......

Dimpled, almost like cross drilled except the holes don't go all the way through.

Slotted, channels or slots spiraling from the center to channel the gasses toward the outside and away from the pads.

Cross drilled, holes drilled all the way through the rotor surface.

Dimpled and slotted appear to be the strongest, but I'm sure someone may have some hard data to back that up.

[hotwhip9]

I've heard what tracez has said, about the cracking with the wholes. Also, this is only what I've heard is that the holes sometimes chew up the pads more or faster. As far as the slotted only rotors go, I've heard nothing but good things. This is only what I've heard, not factual to me or any experience with them my self, but I do plan on getting a set.

[Rob B (shoebox)]

Note in this quote from Baer, that cross-drilling and slotting is considered a "visual enhancement" for street driven cars.

What are the benefits to Crossdrilling, Slotting, and Zinc-Washing my rotors?
In years past, crossdrilling and/or Slotting the rotor for racing purposes was beneficial by providing a way to expel the gasses created when the bonding agents employed to manufacture the pads began to break down at extreme temperatures. This condition is often referred to as “green pad fade” or “outgassing”. When it does occur, the driver still has a good firm brake pedal, but simply little or no friction. Since this normally happens only at temperatures witnessed in racing, this can be very exciting!

However, with today’s race pad technology, ‘outgassing’ is no longer much of a concern. When shopping for races pads, or even ultra-high performance road pads, look for the phrases, “dynamic surface treatment”, “race ready”, and/or, “pre-burnished”. When these or similar statements are made by the pad manufacturer, the pad in question will likely have little or no problem with ‘outgassing’. Ironically more pedestrian pads used on most streetcars will still exhibit ‘outgassing’, but only when used at temperatures normally only encountered on the racetrack.

Although crossdrilling and/or slotting will provide a welcome path to expend any gasses when and if they develop, it is primarily a visual enhancement behind today’s often wide-open wheel designs.

Crossdrilling offers the greatest gas relief pathway, but creates potential “stress risers” from which cracks can occur. Baer’s rotors are cast with crossdrilling in mind, from the material specified, to curved vanes, behind which the holes are placed to minimize potential crack migration. Slotted surfaces are what Baer recommends for track only use. Slotted only rotors are offered as an option for any of Baer’s offerings.

Zinc washing is then done to provide a barrier, which resists development of surface scales or rust.

[Benm109]

I've always had a question about slotted rotors, if someone knows the answer. If you use them and after many miles need them to be turned (on a brake lathe), do you, in effect, take off the slots? I have just always wondered this.

[Joe 1320]

The slots will be there up to the life of the rotor. Once you get to the point that the rotor wears beyond spec, you won't be able to use it anyway.

[Injuneer]

I have Baer slotted and cross-drilled rotors in the rear, and they have not shown any tendancy to decrease pad life. And, so far they have no cracks at the holes. However, I don't really build up a lot of heat in the rotors, since the car is seldom driven on the street any more, and they only have to pull the car down once from 125mph, in a fairly long coast-down stretch of the track, then they are allowed to cool off.

Keith at WS6.com ran the Silver State Classic, in one of the 150mph classes (if I recall correctly), and his Baer cross-drilled rotors started cracking in less than 4,000 miles. He had the replacement Baer cross-drilled rotors o treated, and extended the life of that set to about 19K miles before the cracking became apparent.

http://www.ws6.com/o.htm

I would treat the cross-drilling purely as a cosmetic issue, and avoid them for true "performance" driving... e.g. road racing or auto-X. Apparently they are able to put cross-drilled rotors on Porsches, Ferraris, and now even on Corvettes (C6 optional brakes) at the factory, without cracking problems, so perhaps its just a case of very high $$$$ production techniques being required to insure the integrity of the rotors.

[Benm109]

The slots will be there up to the life of the rotor. Once you get to the point that the rotor wears beyond spec, you won't be able to use it anyway.

Thanks for the info. I had always wondered about that and that clears it up. Thanks.

[02Z28]

and a word about pre-treating rotors, someone on here mentioned once that you can put new rotors in the oven and bake them for 2 - 3 hours at ~350ºF - 400ºF, then just turn the oven off and leave it closed and let them cool down overnight, or however long it takes to get back to room temperature. once they are cool, throw them in the deep freeze for a night, then take them out and let them warm back up to room temp.

[02Z28]

i will personally likely get slotted rotors when i upgrade my brakes. although they probably don't help at normal driving speeds, they will come in handy if you ever need to come down quickly from 130+ MPH

on the track, of course....

[Injuneer]

These are Mark Williams drag brakes.... minimum weight, and just enough to pull a 3,500# car down from speeds up to 160MPH. Note that they are slotted only:



While the car they are installed is capable of exceeding 160MPH, when speeds go over 160MPH, it uses this: