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M3 Track: Racing and DE Best mod for speed is learning to get the most out of what you currently have. Tracks and DE's is the place to start!


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Old Sat, Jul-28-2012, 01:31:38 PM   #1
///MFM3
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Default Rotor Design Question

This has been a longtime question of mine - so I wanted to see what kind of answers I get.

As I understand it, a slotted rotor gives a path for gases produced by the brake pad, as otherwise the gases form a layer between the rotor and the pad (that is difficult to displace, therefore you can't brake well). A cross-drilled rotor just has the advantage of cooling capacity, as there is more surface area. Disclaimer: I have the ZCP brakes on my non-ZCP M3 so I went that route, but as I start tracking my car more, I'm sure I'll go with something cheaper (I hear OEM rotors are buttery from other threads out here), and they will most likely be blanks from a website someone pointed out here a few weeks ago.

So, has anyone, be it a racing team, manufacturer, enthusiast, ever done some exhaustive tests on which design types of rotors actually perform better (all other variables equal), over a track session? This would obviously take something like the same car, back-to-back runs, same rotor size, ducting, caliper, tires, pads, etc, etc.

I have heard that with the newer track/race pad compounds, they don't produce a lot of those gases that the slotted rotor is supposed to combat. I would also imagine that while track/race pads are good up to very high temps, the rotor may not (prone to warping, faster rotor and pad wear).

I guess the thing to do would be to look at what GT race teams use...here's what Turner has on one of their cars (not sure what you call this design):

http://www.facebook.com/photo.php?fb...type=3&theater
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Old Sat, Jul-28-2012, 02:16:11 PM   #2
magnetic1
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Default Re: Rotor Design Question

Cross drilled rotors do not increase cooling capacity. It decreases it as there is less mass. Cross drilled rotors are for aesthetics pretty much. The job of the rotor is to absorb heat, so drilling out mass, leaves you with a smaller heat sink. This is aside from all the other issues relating to cracking, etc.

I'd argue that if youre using a proper pad, that slotting is also for aesthetics too.

As far as the outgassing is concerned, dont really have that issue with current pads. The slotting can help if you end up glazing a pad, but again, proper pad = no glazing.

Turner has "J-slot" rotors. Just more marketing, etc. Just because a GT team uses it, doesnt mean much.
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Old Sat, Jul-28-2012, 09:57:35 PM   #3
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Default Re: Rotor Design Question

Interesting, thanks.

So the best setup is really blanks that can withstand abuse from track pads, the bigger the better (more heat sink).

Given some other threads I've read, I'll be getting some blanks for my next set of rotors.
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Old Sat, Jul-28-2012, 10:34:57 PM   #4
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Default Re: Rotor Design Question

What rotors, slotted, are available to fit zcp setups? I have zcp rotors.... Dislike.... But have Rotora 4 piston front and rear calipers. I'd like to get a set of rotors that are not cross drilled.
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Old Sun, Jul-29-2012, 02:27:14 AM   #5
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Default Re: Rotor Design Question

I'll have to check my subscribed threads...in one of them someone mentions a website with all sorts of manufacturers for great prices. The ZCP setups were much more expensive than non-ZCP the last time I checked though (it's just hit-or-miss).

Edit: the website is rockauto.com. Current ZCP setups are OEM ($230/rotor) or more expensive, while non-ZCP start at $40/rotor...might have to "downgrade."

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Last edited by ///MFM3; Sun, Jul-29-2012 at 02:37:05 AM. Reason: found the website...
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Old Sun, Jul-29-2012, 12:18:55 PM   #6
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Default Re: Rotor Design Question

One thing not mentioned yet are the benefits of a two piece rotor. In general, you'll lower overall rotor weight which reduces spinning weight which I would think extends pad life.
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Old Sun, Jul-29-2012, 01:40:51 PM   #7
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Default Re: Rotor Design Question

Quote:
Originally Posted by ThunderMoose View Post
One thing not mentioned yet are the benefits of a two piece rotor. In general, you'll lower overall rotor weight which reduces spinning weight which I would think extends pad life.
Umm no....has absolutely nothing to do with this!
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Old Sun, Jul-29-2012, 01:47:00 PM   #8
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Default

I really like the 2 piece pfc direct drive rotors.

The pfc rotors withstand wear so much better than the OEM zcp rotors and the replacement cost to the friction ring is about the same as the zcp rotors.
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Old Sun, Jul-29-2012, 01:48:27 PM   #9
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Default

Quote:
Originally Posted by Tarmac_E36_M3 View Post
What rotors, slotted, are available to fit zcp setups? I have zcp rotors.... Dislike.... But have Rotora 4 piston front and rear calipers. I'd like to get a set of rotors that are not cross drilled.
The only 2 piece zcp sized rotor is made by Racing Brakes. Since you can't easily get a new set of carriers, I think your option is rather limited.
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Old Sun, Jul-29-2012, 02:01:17 PM   #10
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Default Re: Rotor Design Question

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Originally Posted by 930man View Post
Umm no....has absolutely nothing to do with this!
You don't think reducing spinning weight would reduce energy that has to be dissipated by the pad/rotors?
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Discussing Rotor Design Question in the M3 Track: Racing and DE Forum - Best mod for speed is learning to get the most out of what you currently have. Tracks and DE's is the place to start! at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)