I am thinking about replacing my rotors with a set of these at the link below:

Brembo Cross-drilled Rotors (http://www.eliteauto.ca/bmwsales.htm)

Similar to these from the M5:.http://www.eliteauto.ca/bmwsales_files/E34M5.jpg

Can anyone compare these to Zimmerman from experience or hearsay. Also if you have a better source for these or the Zimmerman's, let me know. Thanks.

You track that car, don't you?? Or am I thinking of the wrong 7?

If you do, DON'T use cross-drilled rotors unless they say "Porsche" on them. Drilling cast iron gives you lots of little holes where cracks develop. The heat and stress from braking in a track environment will destroy drilled rotors. The way to get around it is to mold the holes into the rotors instead of drilling them. The holes are still a "stress riser", but they are still better than drilled holes.

If you don't track the car, you'll simply notice more noise and the holes will help chew up street pads. Cracks will develop from street use, but they will take longer to notice.

There is no need to go to holy rotors unless you're in a GT, Grand-Am, Trans-Am, or other high-speed endurance track event.

If you find that you are "warping" rotors at the track, get brake ducts and pads that will take the heat. Technically speaking, you rarely "warp" rotors from too much heat. You actually get uneven pad material transfer onto the rotor surface. Since the coefficient of friction from pad/pad contact is higher than pad/iron contact, you get a pulsation through the steering wheel.

JamesM

James,

Thanks for the quick reply and the good advice. I don't track my car, Simeon is probably the E38 that you are thinking of. :D My car is just for street and to look "pretty", which is the reason for the interest in cross-drilled rotors. :)

I know Zimmerman's cross-drilled rotors are cast so will probably look into them if I decide to go this route. Other opinions are all welcomed guys.

Later,
Mike D.

Anyone with cross drilled or the slotted rotors, what kind of "extra" noise or sounds develop from installing them? Some folks have said they make your brakes louder or something. ANy comments?

High-speed braking produces this weird whirring noise. You may notice a scraping noise on a street car.

Zimmerman's rotors are drilled, also. Casting a rotor with holes in it is very expensive, which is why you'll only see them on Porsches, Ferraris, and real race cars. Performance Friction and others make racing rotors, but those are for building your own brake systems, not for OEM replacement parts.

I would just stay away from holy rotors altogether unless I were building an endurance racecar.

JamesM

Originally posted by JamesM3M5
...
Zimmerman's rotors are drilled, also. Casting a rotor with holes in it is very expensive, ...
JamesM

JamesM, thanks for the information and your input, I do appreciate it, but I see the following posted on most sites selling Zimmerman's...Turner Motorsports, Zygmunt, etc.

Zimmerman Cross Drilled Brake Rotors:
http://www.turnermotorsports.com./image/banners/red_line.gif
We have finally found a cross drilled rotor worthy of selling. These rotors are made in Germany by Zimmerman, one of the largest OE brake supplier to most German makes of cars.
The holes in these rotors are not drilled in after the manufacturing process but are actually cast into rotor. Therefore, cracking between the holes is a lot less likely.


Thanks again.

I have the Zimmerman's - actually a lot of people do. I don't track the car - they just look really nice with my summer wheels on. I have had no problems with them and they stop nicely. One problem is that they are loud compared to stock. A lot louder actually. But otherwise they are nice.

I'm on my second set of Brembo Cross-drilled rotors and I've never had a problem. I love them.

They look great.

Originally posted by Ryan325i
I have the Zimmerman's - actually a lot of people do. I don't track the car - they just look really nice with my summer wheels on. I have had no problems with them and they stop nicely. One problem is that they are loud compared to stock. A lot louder actually. But otherwise they are nice.

I'm gonna have to agree on that one. i thought i did something wrong! it sounds like a turbine when i brake hard! oh well, they look cool!

Mike -

I have cross-drilled Brembo's on my car right now at all four corners. My mechanic recommends Brembo's over Zimmerman's, and even more preferably, euro floating rotors or BBK.

The cross-drilled Brembo's are holding up very nicely. The only thing that I would recommend with cross-drilled is inspecting the rotors periodically (maybe quarterly). If you visit the track forum or maybe OT, I posted a week ago, someone put on brand new zimmerman's IIRC on their car, the rotors completely disintegrated on the track, the car flipped over and went smush. That's one of the problems dealing with cross-drilled rotors.

I know people always set forth the argument, well, I don't track my car. Regardless, this occurred braking from 80 mph, so, definitely something that could occur on the street. The other argument is that manufacturing defect. Not necessarily true. Thinking logically, having holes in something versus not having holes, which one would be structurally stronger.

That said, I don't think you'll have any problems with cross-drilled rotors. Just be careful in washing them. For instance, say you drive the car in some traffic and stop by a car wash, cold water on hot rotors -- might not be a good idea. So, with routine inspections, I think you'll be fine. They definitely do look nice!

P.S. - as far as why Zimmermans's are not preferred by my mechanic over Brembo's. I can't answer definitively why. He argues that the quality is not as good in his opinion. Since he's a BMW tech ... and been around for 20+ years, I pretty much follow his opinions.

Umm, thanks James and DOO. I went with the Zimmermans last year with no problems... not exactly sure why DOO brought up this *year old* thread. :rolleyes: ;)

- Mike

I'm guessing tha Doo did a search, then replyied, forgetting that he was on an old thread - it just happens!

Well, do you think they're loud?