Contour Enthusiasts Group Archives Forums Modifications Brakes Slotted Rotors - Revisted

Please read this entire thread as it addresses common misconceptions! And again be sure to read the FAQ
-Andy

The only thing i have heard bad about the slotted rotors is that they eat the pads just a tad bit faster, but they do help in performance. Is there any truth to this? I doing my front and rear brakes and want to upgrade it to have good street performance. Im going to be running Hawk HPS pads with whatever i go with.

From what I hear they don't help much/at all for street performance and they will eat up pads.

What Kremit said. They are not as problematic as the Cross-drilled rotors, and they actually do have a performance benefit under some circumstances.

But they do cause your pads to wear faster, and they are not optimum, performance-wise, for anything but the most extreme, high speed, repeated-hard-braking situations. Hence, you probably don't "need" them.

Mod Edit: There are many misconceptions in the statement below, see Silver Snake's explanation further down.


All the slots are for are for additional cooling (more air flow & surface area) and will only benefit you in an instance where you're using your brakes a lot such as a track event, auto-x, racing, et cetera. For a daily driven car they're a waste and overkill IMHO. As the other posters mentioned they'll wear the pads quicker than standard rotors, will typically warp easier since they're not quite as sturdy, and can potentially crack near the slots too thus making them not as structurally sound (although not nearly as likely compared to cross-drilled ones). They do look kinda good though so if that's what you're going for then I suppose they can be worth it then. Just my $.02

Good stuff, thanks for the info everyone. Im just going to go with brembo blanks.

Can't go wrong with Brembo's (damn this sounds like bimbo's)

Originally posted by JohnnyBravo:

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All the slots are for are for additional cooling (more air flow & surface area) and will only benefit you in an instance where you're using your brakes a lot.....

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Actually, slots are not for cooling, airflow or surface area. Slotted discs are used to clean the pad or "wiping the fire-band" as its called in the industry. The slots sole purpose is to clean the top layer of the pad, and prevent glazing of the friction material surface. By maintaining a clean even surface, friction level or mu can be kept more consistent from stop to stop.

Originally posted by airman1:

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Slots are there to help remove the fumes and brake pad vapor occuring after hard braking, thus helping in cooling of the pads not rotors/discs/...

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No they are not. Please see above. Fumes are no longer an issue with modern brakes (last 20yrs), as pad out-gassing doesn't occur due to new manufacturing techniques and materials.

Originally posted by airman1:

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Will slotted rotors crack easier than non-slotted ones? Maybe...

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Yes. Always.

Originally posted by airman1:

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Drilled rotors, regarding cracking, are acctually safer that non drilled because crack would stop at the hole and would not spread, while non-drilled rotors if they crack, it's over.

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This just isn't correct. There are too many factors at play. I can show you drilled rotors that show crack propagation twice as big as solid rotors. It has to do with rotor design, cheek thickness, venting design, etc. There are too many factors at play to simply say "X rotor is better because its drilled"

Originally posted by airman1:

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Rotors are drilled for weight savings and looks alone, there is no heat benefits in drilloing of the rotors.

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Wrong. Appearance plays a major factor in rotor cross-drilling, that much is true. However, for automotive use (not motorcycle) weight is never a factor. The weight savings from a drilled rotor is insignificant. Its done for appearance and slight performance gains. If the rotor is thermally sized properly (i.e., it has enough thermal mass), x-drilled holes allow for slightly quicker cooling (at a loss of thermal mass). However, they will crack quicker than an identical solid faced disc. The performance gains are slight, and not one that will be noticed by even the most discriminating street driver.

Originally posted by airman1:

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There is one concern with drilled rotors. Moisture, and water dropplets can accumulate in those holes and eventually end up under pads, thus creating a problem.

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Actually, testing performed by both Brembo and Porsche has shown that x-driled rotors offer improved perfomrance in wet effectiveness. In simple terms, it gives moisrture and water vapor a place to go, instead of forming a boundary layer under the pad.


Not trying to be a jerk, just trying to "correct the tech".

Good info, Snake.

Any time.

Thx for stepping in Silver Snake, I got through most of the thread already composing a reply in my head; until I got to your post . . . you covered it much better than I would have . . .

btw, Have you hit any small animals w/ Hispanic names w/ your Enzo yet?

(Taking his own foot out of his mouth)
It sucks to be wrong, only thing that helps is when you get good info. Thanks for correcting me. Reasoning I used about cross drilled rotors and cracks is logic that if they crack it will not go any further than the nearest hole (it shouldn't anyway). The info on water droplets was acctualy from motorcycle world, I was not aware of testing done by Porsche (I aware that they test it, not aware of the results). Still I am not impressed by cross drilled rotors and the results they got. As for the weight savings well we are not talking about total weight savings, but about unsprung weight, and there are the differences, smalll though. Anyway thanks for correction.

What you may not realize about drilled rotors and cracks is that the holes themselves are the stress risers that encourage the cracking. The cracks START at the holes.

I guess I stand corrected as well. When I was shopping for a big brake kit for my former RX-7 TT (was going with AP's instead of Brembo's though) I researched them quite a bit and I guess even those folks selling the products don't always know all the correct info all the time. Oh well either way you can't go wrong with anything Brembo makes as they do take their products seriously as far as I can tell. I mean many top supercar manufacturers use them on their production & race cars so I guess they have to be somewhat good

FAQ:

What are the benefits of cross-drilled/slotted rotors?
The simple answer is asthetics! Slotted and cross-drilled rotors do not improve braking nor is the weight savings beneficial. Often, the slots and holes cause quicker pad wear and shorter rotor life due to cracking and warping. You've hard that the unspring weight savings can help greatly, false. It is beneficial on a vehicle as weight sensative as a motor cylce but not on a street car like the a Contour. Your best bet for good braking and pad/rotor life is a quality set of blanks!

Somebody make this a sticky and lock it before the "but but but" crowd chimes in.

Will Do! Please read the Entire FAQ before posting!

Ok, so.....

http://www.reddotracing.co.uk

Scroll down now......you know if 1 is good, then 2 is always better.

Sorry Todd,
But I would not take advise on this subject from a company that uses a x-drilled rotor in their logo.

-Andy

Well, you know how toilet paper never seems to tear off at the perforation. I guess they applied that theory to their rotors.

There are a lot of misconceptions about slotted and crossdrilled rotors. I have read many of the posts in this forum and feel that I can add some helpful information. I have been in the performance brake and racing industry for a number of years and this is what I have learned from my own experience and the experience of others. Slotted rotors and crossdrilled rotors have absolutely nothing to do with keeping the brakes cooler than stock rotors. The main advantage to using slotted or crossdrilled rotors is that they will allow the brakes to operate properly at a much higher temperature than will stock rotors. When brake pads get hot,(even the newer friction formulations) the resins that bond the friction material together develop rise to the surface of the pad and develop a gas. This gas will actually float the pad away from the rotor. The same theory which makes engine bearings last so long, there is never any metal to metal contact because there is a very thin cushion of oil separating the two parts. Generally if the brakes get hot enough, they will lose their effectiveness and a spongy pedal will usually result. This spongy pedal is caused by one of two things; boiling brake fluid or the fact that you are trying to compress the gas that is floating the pad away from the rotor. What slotting and crossdrilling does is to allow a path for this gas to dissipate, while allowing the pad to maintain a good, solid, contact with the rotor, thus maintaning effective braking. Slotted rotors accomplish this much better in everything except all out race cars because they generally have a much longer life expectancy than crossdrilled rotors. Crossdrilled rotors usually crack because when cast iron parts are drilled, stress risers are developed which generally develop cracks after many consecutive heat cycles which can ultimatly lead to rotor failure. Additionaly, crossdrilling removes significantly more friction surface area from the rotor than slotting does, allowing a lower braking capability over stock or slotted rotors. The only real advantage to crossdrilled rotors is the reduction of unsprung weight that they offer, which makes for a considerable handling advantage in all out race cars. And the cracking isn't an issue, because very few heat cycles are seen before the rotor is replaced. Slotting does everything that crossdrilling does, with the exception of the weight reduction issue. The only difference is that they very seldom crack, they do not eat the pads as fast as crossdrilled rotors, and because they have more friction surface and mass than a comparable crossdrilled rotor, warping and temperature are greatly reduced. I hope this helps anybody who is interested...feel free to email me if any questions come up @ pmccle3928@aol.com

Pat,
Your talking about extreme race situations. Not situation faced to street car owners or even auto-x car owners. Not to mention the materials used in those brakes are something that will probably never be produced for our cars.

-Andy

I've had Powerslot's on the front (278mm) for over 4 years and 25k miles now. No warping or squealing, but a bit of a groan under hard braking. I put in new stock Ford pads with them and they are about half worn now. I see no problems in using them at all. The right one even survived a seized caliper for a few miles. I have had to clean the grooves every 6 months or so though.

25k Miles over 4 years is not heavy use, but I'm glad you are having success.

-Andy

I thought I'd add one more tid-bit of info. I've had my Powerslots for almost two years. Not once have they squeaked or squealed. I don't know if that is common with all slotted rotors, but it is nice to say the least.