Cross-drilled rotors can be used effectively to compensate for other problems encountered in brake system design. The biggest one would probably be heat rejection (which is also why most OEM rotors now are "vaned"), followed by gas buildup from the pad material. They're not always a waste, and they haven't been shown (in my personal experience, which includes racing) to decrease performance by any measurable amount.

Slots can also help with pad gas rejection.

Most sprint cars use cross-drilled rotors, as do racing series with small cars and that mandate iron rotors. F1 uses carbon-ceramic discs. You'll see slotted/cross-drilled rotors on cars that are geared more towards trackday fun than otherwise, because the heat rejection limits brake fade.

The other issue I have is with this new forum vendor/sponsor/whatever and "cryogenic" rotors. What does this accomplish, exactly, in the iron rotors? You're clearly looking at some sort of tempering/heat-treating factor, but I can't find any reference to it in my materials or manufacturing texts. Grey cast iron is still the way to go, unless you can still get your hands on exotic stuff like Al-MMC or carbon (yummy).

 

Modern pads don't produce the gasses that older pads did.

 

Crappy karting brake pads (and some old school Wilwood compounds) do

 

I don't know of any crappy karting pads that will fit on a 2IS, but why not just use good modern pads instead of crappy cross drilled rotors?

 

we get it, gernby= no crossdrilled rotors

 

It's not just him... pretty much anybody that knows brakes will tell you cross-drilled=crap on a street driven car. (and most track driven ones too, with a few odd exceptions).

If you care more about show than go there's no shortage of folks that'll sell you cross-drilled rotors though, usually using 1950s brake pads or a misunderstanding of thermodynamics to explain why you should buy em.

 

On street-driven car? Does doing hot laps at Laguna Seca count as "street-driven"? I can understand the dangers of using cross-drilled rotors in a track scenario, but for ordinary street and freeway driving, I honestly don't see the big deal. Cross drilling is clearly a 'bling' thing, but telling somebody that their rotors are going to crack when the hardest braking they do is at a stop light is a bit over the top (assuming you're using a quality disc and not drilling them yourself or using some cheapo ebay garbage).

Javier

 

I think this is another key point that was also brought up in the other thread about drilling rotors. The quality rotors will have all the drilled edges chamfered to reduce any stress risers from the sharp edges. In the end, its this that causes the crack to begin.

Gern, I don't know of anyone who makes crappy karting pads for the 2IS either. But that was where my experience with drilled rotors came from.

 

I had slotted Powerslot rotors and Hawk HPS pads on my STI and I loved them...

 

it is just sort of hard to believe that the porsche gt3, bmw m5, audi rs4, all the lamborghini's, all the ferarri's have drilled rotors and they have spent millions on research and development to see who could stop the best, and your telling me this is all a bunch of bull? Hard to believe is all. Who would you trust, all the major car racing companies, or someones theory on some website. everyone should just make there own decision.

 

How about someone who's raced in One Lap and had to replace his drilled rotors because they cracked and nearly disintegrated?

The manufacturers are not putting holes in the rotors because it works better. They put them there because most car buyers don't understand physics. They want something to show their friends and impress them. So they drill and slot.

If you read Pulp Friction, you'll understand braking from a real engineer's perspective. The guy who wrote the article is world renowned for brake and stability control engineering. He could work at any of the manufacturers as their lead engineer, and he frequently teaches classes for the Society of Automotive Engineers (SAE).

You might want to think it's hard to believe, but if you understand the physics and material science, it isn't hard to believe at all.

 

Grooved, drilled rotor. The drilled holes again give more bite, but also allow air currents (eddies) to blow through the brake disc to assist cooling and ventilating gas

Drilled rotors are typically only found (and to be used on) race cars. The drilling weakens the rotors and typically results in microfractures to the rotor. On race cars this isn't a problem - the brakes are changed after each race or weekend. But on a road car, this can eventually lead to brake rotor failure - not what you want. I only mention this because of a lot of performance suppliers will supply you with drilled rotors for street cars without mentioning this little fact.

to say that drilled rotors don't increase braking potential is just not right. to say that they are not for track use if you don't want to replace them alot is correct.
lobuxracer is right in that the rotor will be weakend, but if you can understand thermodynamic principles, drilled rotors allow increased surface area to be exposed to the air for better cooling, simple thermodynamics. Also I like them because they are blingy.

 

Drilling reduces mass, which means they can absorb -less- heat.

THAT is pretty simple thermodynamics.

And unless you're driving on 50 year old brake pads there aren't any gasses in need of venting either.

 

drilling increases surface area exposed to air which leads to increased heat transfer. An easy way to think of it is to picture an ice cube, Which melts faster a solid ice cube or one with holes in it? The one with holes in it because there is more surface area exposed to transfer heat. Now that is thermodynamics in a nutshell. Although this whole topic is like beating a dead horse, if you like drilled rotors get drilled rotors, if you don't then don't.

 

This isn't always true, and is totally dependant on the thickness of the rotors and the diameter of the holes. If the rotors are really thin, and the holes are relatively large, then surface area can actually be reduced. I've seen cross drilled rotors on motorcycles that I'm sure had less surface area than a non-drilled derivitive would have.