Grooved vs Drilled Rotors

Maybe post in the tech section?

 

http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml
http://www.stoptech.com/tech_info/tech_white_papers.shtml

Mainly, Grooved will be less susceptable to Cracking, the "Warping" issue being addressed in the first of the above links. An otherwise overlooked advantage to the Drilled Rotor is the removal of mass, both static and rotating, BUT (!!) is more than offset by that loss of mass being detrimental to the amont of metal for heat storage and dissapation. The minimal gassing of current pads is more than addressed by simple grooving, and really unnecessary, better for just cleaning the pads of water in rainy conditions.

The main reason for the continuation of Drilled Rotors on production cars is Marketing - it's "Old School Heritage" from when there really WAS (note the past-tense there) a gassing issue. As for those cars still using the Drilled rotors, refer to the previous sentence.
The biggest contribution Drilled Rotors make these days is to the Image of Mfr. ABC's model XYZ Super-Duper Turbo Exotica (Look!! It's got Drilled Brakes!!!), and to the replacement market who sell to Track-Day folks who don't know any better. I have more than one friend who has "the prettiest set of Brembo Cross-Drilled Rotors" hanging on the garage wall, cracked all over (one, with a nice chunk missing); FINALLY replaced with plain rotors after a set or three and no more drama. Ever see what one of those lightweight, swiss-cheesed platters will do to a Technomagnesio wheel when a series of those cracks give-up? It ain't pretty.
Admittedly, the car did sound pretty neat under heavy braking until that point.

If you have experienced actual warping, odds are that you've come down from speed, and sat with your foot on the brake pedal, holding heat under the pads while the rest of the rotor cooled. Either way, that action will give you either the warping or the deposits that you feel. I never sit at a light with more than the parking brake on only as much as needed - holds the less-heated rear brakes, and even if a pad deposit is left on the rotor, it's not where the heavy braking is done. Haven't had a problem since I started doing this, years ago.

 

That's the bottom line...slotted has risen in the market as an alternate to drilling and is less prone to generate cracking......

 

Just added that last paragraph, might give you a bit more insight that I forgot about originally.

 

Mercedes actually cast their "drilled" rotors with holes, instead of drilling holes, probably for the reasons discussed here.

 

Grooved are better........

 

The cast (drilled) rotors are less suspectable to cracking than standard drilled rotors. But, I put slotted/grooved rotors on a Porsche some years ago and found them quite effective. They were recommended over drilled by a guy (Clay Dopke) who race prepped 'em for a living.

I've followed his advice ever since, and had great luck with the slotted/grooved rotors on a variety of cars.

DM

 

For those who still like the drilled look, I have seen them with dimples instead. When the dimples fill with brake dust they look "drilled" . The benefit is they are less prone to cracking while keeping the drilled look .

 

I just ordered new Brembo rotors for my daily driver BMW 540 M-Sport...I just got the normal, oem, axially vented ones...I'm "old school"...

Oh, and Porterfield R4S pads, can't wait to get them installed.

 

I have slotted and drilled 11" discs on the front of my car, with four-piston racing calipers and sport pads. The amount of fade has been reduced dramatically and I've yet to warp one of these rotors (and believe me, I try). Warmed up, they squeak like a rabbit in a fire, but I could care less about that. Since upgrading to this kit, I have not locked up my brakes once.

 

Excellent, what ya drivin' these days?

 

LOL, a bone stock (except for the brakes) Nissan Sentra 2.0 SE (automatic).

 

Drilled are for looks, grooved are for business. I think CCM might be an exception here

 

I have a ton of experience with this one....


If you are driving on the street, "drilled" rotors are fine. It is quite simply impossible to push your car hard enough on the street to generate the kind of repetitive heat cycling that will cause cracking while driving on the street. This is assuming your using quality rotors where the holes are cast into the wheel and not in fact literally drilled. Rotors where the holes are literally drilled are garbage, dont waste your money.

If you are going to drive on the track..... then the cast drilled rotors are just not going to last. If your not pushing the car all the way to the edge you will get decent use but when you get to the point where you really are "fast" the drilled rotors are simply not up to it. In my '69 911S track car using brembo cast drilled rotors that had also been cryogenically treated I could get at most 3 weekends at the track. I went through 3 such sets and 2 sets I got 3 weekends and the other only 2 before the cracks spiraling out from the holes began to connect with each other and the edge of the rotor. This is most Road Atlanta use and I do brake very hard.

I switched to slotted rotors and so far got 6 weekends and the rotors are fine.

With slotted rotors you will need some ducting as I do not believe they dissipate heat quite as well but even some rudimentary ducting and you should be fine.


Terry

 

Jim your car should have ducting to the front rotors anyway, which helps. Both my 355 and my BMW 540m-sport have them standard from the factory