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Suspension & Braking
Have some questions about suspension or brake setups for your E46 BMW? Get all your answers here!

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Old 03-01-2007, 12:10 PM   #21
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Originally Posted by FTLAUDM3 View Post
I still find it hard to believe that the drilled are dangerous. Mercedes, Audi, Porsche, BMW, and any sports car use em. After reading this thread I guess they are all done the proper way though. Every BBK (Brembo, Stoptech, Wilwood, Rotora, etc) all use em. The question is how are they made....
Marketing is amazing in what it says and what it does not say so clearly...

Stoptech very specifically does not recommend their drilled rotors for track or race use.

Please read what I wrote about about cast-perforated versus drilled rotors. An aftermarket drilled rotor is definitely not the same as the OE rotors.

- Rob
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Old 03-01-2007, 01:26 PM   #22
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Then you're not using them hard.
You are correct. I never took that car on a road or autocross track. That combo was better than stock on my Stealth RT/TT, and did fine to get get the car down from 115 before the end of the run out, which was all I was looking for.
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Old 03-01-2007, 01:38 PM   #23
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Which brings up an interesting point on wheel size. Anything over 18" and less that 45 aspect ratio is the same thing=fashion fad. If the fashion fad is race car like drilled rotors why isn't the fashion fad Forlmula 1 like small wheels and big tires? There's no predicting those fashion fads!
They run 13" wheels because of the rules.....
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Old 03-01-2007, 02:09 PM   #24
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Holes are holes - all the way through. Not dimples.

Normal post-casting cleanup maching takes place, no different than any other rotor... the rotor face, edges, inner and outer hub faces, and casting flash within the holes. When you look at a rotor, every surface that is not rough has been machined.

- Rob
I don't suppose you have any pictures of the rough castings (or the molds) showing the cast in holes? I understand that would be a rather complex process and I'm curious to see how it is done.
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Old 03-01-2007, 04:40 PM   #25
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Well, if you want the rotors just for looks, and not performace go for it. Dont think you will be cracking them, unless you drive your car hard. I got the brembo sloted/drilled, have not given me any trouble. But for performace or auto X i would go with just slotted.
Uh-uh.

I do so love these forums....so many questions that ASK, yet when the right and correct answer is given, its refused and then the discussion comes along until the poster finally gets an agreement on the answer he wanted in the first place.

Sheeesh.

Drilled rotors crack. Doesn't mean they're dangerous, but they crack at the holes. Ever seen a rotor explode on a moving car? They do, and they tear up a lot of things when they do (guaranteed to gouge your pretty aftermarket wheels). Your might not crack for a month, or a year, but they eventually will. Then its best to toss them.

If you want REAL performance then the key to braking is controlling heat in the rotor. You do that by using floating rotors, which means the hub area is made of a different material than the rotor itself, and designed to dissipated heat. Still too hot? Then you duct your brakes (don't try this on the street, kiddies, you'll tear the ducts off at the first turn into the shopping mall).

I've run an E36 M3 as fast and as hard on a race track as it can go, and have always had plenty of brake with floating rotors, ducting and true race compound pads.

Buy those drilled rotors because you think they're SEXY, but that's it.
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Old 03-01-2007, 09:00 PM   #26
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Thanks for all the responses guys! Seems to be quite a bit of quality input in this thread.

Quote:
Originally Posted by Rob Levinson * UUC Motorwerks View Post
Excellent question!

The rotors we use in the big brake kit are genuine BMW Motorsport rotors, which are apparently cast-perforated, not actually drilled.

The difference is that the holes are cast into the rotor, so the metallic grain structure (and therefore the strength) is not compromised as with conventional drilling.

Please note that we are in the process of updating our website pricing on brake rotors.

I think that you will find our new Gen2 black rotor regular pricing is better than "group buy" pricing for other brands.


New package options include SS lines, pads, fluid, at pricing below regular single-item pricing.

Please see: http://www.uucmotorwerks.com/rotors/ and click on your application for options. Please note - not all applications updated yet, if your listing does not show all options, please call us for pricing!

- Rob
I think this is what I will probably go with. Thanks for the info Rob! BTW when looking at rotors is there any way of telling if the holes were drilled vs. cast into the rotor?
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Well, if you want the rotors just for looks, and not performace go for it. Dont think you will be cracking them, unless you drive your car hard. I got the brembo sloted/drilled, have not given me any trouble. But for performace or auto X i would go with just slotted.
At this point I am sure I could go with cross drilled and be just fine. I hardly every drive my car hard and never track it. But I don't think it would be worth it anyways
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Old 03-06-2007, 11:27 AM   #27
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Having looked in to this rather thoroughly, I am certain that there is no such thing as a rotor with cast-in holes in the rotor face. Making a rotor in such a fashion would be prohibitively complex, if not downright impossible.

There is however, a very significant difference between rotors designed and cast with the intent of drilling them later and rotors designed and cast as solid rotors which are later modified by cross-drilling. This is what explains why "An aftermarket drilled rotor is definitely not the same as the OE rotors." as Rob put it earlier

In the former category, there are only two manufacturers that I am aware of that do this - MOV'IT and SHW. While the holes in the rotor face are still drilled, the design of the rotor, particularly the vane structure, is cast in such a way as to accomodate these holes.

It might be considered a minor distinction, but hopefully it clarifies the distinction and meaning of cast holes vs. drilled holes.

BTW - if anybody has contradictory proof in the form of picture of a rough casting or mold showing cast in holes in the rotor face, please post it. And PM me and I'll tell you how to get some $$$ in exchange for it.
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Old 03-06-2007, 12:02 PM   #28
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Having looked in to this rather thoroughly, I am certain that there is no such thing as a rotor with cast-in holes in the rotor face. Making a rotor in such a fashion would be prohibitively complex, if not downright impossible.
You and I discussed this in private e-mail, I know I've seen further documentation on it.

It wouldn't be any harder to cast holes in the external face than it is to cast the entire vented central section - that would be the hard part.

Quote:
There is however, a very significant difference between rotors designed and cast with the intent of drilling them later and rotors designed and cast as solid rotors which are later modified by cross-drilling. This is what explains why "An aftermarket drilled rotor is definitely not the same as the OE rotors." as Rob put it earlier

In the former category, there are only two manufacturers that I am aware of that do this - MOV'IT and SHW. While the holes in the rotor face are still drilled, the design of the rotor, particularly the vane structure, is cast in such a way as to accomodate these holes.
Actually, there are other companies that can... it's whether they choose to or not.

- Rob

Last edited by Rob Levinson * UUC Motorwerks; 03-06-2007 at 12:05 PM.
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Old 03-06-2007, 02:10 PM   #29
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I know I've seen further documentation on it.
And I'm looking forward to seeing it or whatever other info you can dig up.

In the meantime, I thought I'd make the appeal for information/evidence to a larger audience on the chance someone might just have some insider info on this.
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Old 03-12-2007, 09:41 AM   #30
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Here's an interesting tidbit from Wilwood Engineering's website -
Quote:
Caution on drilled rotors: There is a common mis-perception that rotors are drilled to improve cooling. The reduced mass of a drilled rotor will dissipate its retained heat quicker, but it also builds up heat at a much faster rate. The decision to use drilled rotors should be solely based on the merits of the lower rotating and unsprung weight, and not for improved cooling. It is not wise to use drilled rotors in sustained high heat on hard braking tracks unless the team budget affords a high frequency of rotor and brake pad replacement.
Additionally, all the holes in the Wilwood rotors are specifically described as being drilled.

Wilwood's website is here - http://www.wilwood.com/INDEX.ASP
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Old 03-12-2007, 10:02 AM   #31
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Here's an interesting tidbit from Wilwood Engineering's website -


Additionally, all the holes in the Wilwood rotors are specifically described as being drilled.

Wilwood's website is here - http://www.wilwood.com/INDEX.ASP
Yes, you're quoting a section that I have quoted several times. We don't supply Wilwood drilled rotors at all.

I am missing the point you are trying to make.

- Rob
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Old 03-12-2007, 10:33 AM   #32
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Yes, you're quoting a section that I have quoted several times. We don't supply Wilwood drilled rotors at all.

I am missing the point you are trying to make.

- Rob
Not trying to make a point, just adding info.

Typically, drilled rotors are touted as having benefits due to either improved cooling, pad gas escape, etc, etc.. Wilwood's explanation is the most clear and concise explanation I've seen of the only real benefit they offer - reduced weight - and the trade-off you have to accept for that - increased need for rotor and pad replacement.

Didn't mean to imply that you supplied Wilwood rotors. If I understand correctly, your kit couples a Wilwood caliper with a BMW Motorsport rotor.

And regarding the BMW Motorsport rotors, I still can't find anything that documents them as being cast with holes. Everything I've found describes them as "factory drilled". Unfortunately, SHW's website has no detailed information on the subject.
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Old 03-12-2007, 12:48 PM   #33
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Regarding BMW Motorsports rotors, here's BMW AG's description of them from their "Technology Guide"
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To safely master their staggering power and performance, BMW's M models come with a particularly efficient high-performance brake system featuring compound brake discs. The big difference compared to conventional brake discs is that compound brake discs feature a radial anti-friction bearing for the brake disc ring.
This floating system allows free thermal expansion of the brake disc rings, thus providing the option to use different materials with the best properties in each case for specific purposes. This, in turn, means that each component within the brake system is able to do a perfect job according to its specific requirements.
The result is not only outstanding stopping power, but also a considerable reduction in weight versus conventional brake systems, a significantly higher standard of driving comfort and a much longer service life.
Reading between the lines, I think it is interesting that rotor holes are not even mentioned. One would think that if they featured cast-in perforations rather than drilled, this would at least get a passing mention as a techinical advantage. Additonally, in BMW's M-series spec sheets, the rotors are described as "Compound disc brakes, inner-vented front and rear, drilled"
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Old 03-12-2007, 01:26 PM   #34
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Regarding BMW Motorsports rotors, here's BMW AG's description of them from their "Technology Guide"

Reading between the lines, I think it is interesting that rotor holes are not even mentioned. One would think that if they featured cast-in perforations rather than drilled, this would at least get a passing mention as a techinical advantage. Additonally, in BMW's M-series spec sheets, the rotors are described as "Compound disc brakes, inner-vented front and rear, drilled"
I think if you read enough BMW literature through the years, you will find the occassional translation oddity. For example, some brackets are called "suspension" simply because the translation is "off".

Bottom line: you're not going to find anything overwhelmingly specific in a technical sense when the terminology has the vagueness of translation.

In the literature I've seen from all the OE companies such as Porsche, Mercedes, and BMW, the rotors are always listed as "perforated".

BMW ETK screenshot for M3 CSL:



- Rob
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Old 03-12-2007, 01:30 PM   #35
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The question is not whether or not they are perforated, the question is whether they are cast perforated or drill perforated.
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Old 03-12-2007, 01:36 PM   #36
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The question is not whether or not they are perforated, the question is whether they are cast perforated or drill perforated.
Yes, but my response is to the inference you made that a single piece of BMW literature, using a term used nowhere else in the BMW literature, is of any conclusive value as to the method.

It's important not to confuse an issue with anecdotal details of neutral significance.

- Rob
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Old 03-12-2007, 01:47 PM   #37
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At the end, I think we can both agree that the result is this - there is no conclusive evidence to be found in any BMW literature on whether the holes in the rotors are cast or drilled.

The point where I suppose we diverge is what the default answer is:
Are the rotors assumed to be cast perforated unless proven to be drill perforated?
- or -
Are the rotors assumed to be drill perforated unless proven to be cast perforated?

Being a big fan of Occam's Razor, I think the latter supposition to be the better one.

BTW - What makes the reference in the product datasheet to "drilled" rotors interesting is that it is the only process reference that can be found. Elsewhere in their literature the rotors are either simply described as perforated or no mention is made of it at all. At no point are they ever described as cast with holes. But I do agree that this hardly constitutes conclusive proof on two points - (1) could be a translation quirk (although it is hard to imagine them similarly confusing cast and forged) and (2) drilled might be being used as a synonym for perforated, such as using Kleenex and tissue interchangably.

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Old 03-12-2007, 02:35 PM   #38
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There is still a preponderance of literature suggesting cast holes.

At best, I think the only thing that can be agreed upon is that getting the OE casting houses to divulge their proprietary and patented manufacturing techniques in order to answer your assertions is at best difficult, at worst impossible.

- Rob
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Old 03-12-2007, 02:36 PM   #39
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i have stoptech slotted rotors and love them!
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Old 03-12-2007, 02:58 PM   #40
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There is still a preponderance of literature suggesting cast holes.

- Rob
For being a preponderance, it's awfully hard to find.

Here's what I know so far -
* MOV'IT - states their holes are cast, but once you get in to the details, it turns out they mean that channels are cast into the vanes. The actual holes in the rotor face are made with a 4.3mm drill.
* Brembo - holes are drilled, not cast
* StopTech - holes are drilled, not cast
* Zimmerman - holes are drilled, cast
* Wilwood - holes are drilled. not cast
* Racing Brake - holes are drilled, not cast
* AP Racing - holes are drilled, not cast
* Performance Friction -holes are drilled, not cast
* SHW - makes no direct claims, but are the manufacturer of Porsche and BMW Motorsports rotors.
* Porsche - holes are drilled, not cast
* BMW Motorsports - as discussed above, there is no evidence to suggest they are cast.

If you can provide a link, attachment, picture of a rough casting or mold, or any literature about somebody making a rotor with cast-in holes, I'd be most grateful.
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