E46 BMW Social Directory E46 FAQ 3-Series Discussion Forums BMW Photo Gallery BMW 3-Series Technical Information E46 Fanatics - The Ultimate BMW Resource BMW Vendors General E46 Forum The Tire Rack's Tire Wheel Forum Forced Induction Forum The Off-Topic The E46 BMW Showroom For Sale, For Trade or Wanting to Buy

Welcome to the E46Fanatics forums. E46Fanatics is the premiere website for BMW 3 series owners around the world with interactive forums, a geographical enthusiast directory, photo galleries, and technical information for BMW enthusiasts.

You are currently viewing our boards as a guest which gives you limited access to view most discussions and access our other features. By joining our free community you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is fast, simple and absolutely free so please, join our community today!

If you have any problems with the registration process or your account login, please contact contact us.

Go Back   E46Fanatics > Tuning & Tech > Suspension & Braking Forum by BimmerWorld

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

Reply
 
Thread Tools Search this Thread Rating: Thread Rating: 8 votes, 5.00 average. Display Modes
Old 03-24-2007, 05:15 PM   #1
jpr
Registered User
 
Join Date: Aug 2005
Location: San Diego, CA
Posts: 3,005
My Ride: '99 323i
BMW brake rotor facts and deductions

Here's the real answers to what seem to be the FAQ's. The facts are taken direct from the TIS, the deductions come from my engineering background. As always, please do not hesitate to identify and correct any errors I may have made.

Rotor sizes (in mm)323 - 286x22 front, 276x19 rear
325/328 - 300x22 front, 294x19 rear
330 - 325x25 front, 320x22 rear

Minimum Acceptable Thickness for reuse -
323/325/328 - 20.4mm front, 17.4mm rear
330 - 23.4mm front, 20.4mm rear (deduced)

Maximum Allowable Runout
Disc on it's own - 0.04mm
Disc installed - 0.2mm

Is it allowed to machine (turn) BMW rotors?
Yes, there is an actual BMW procedure in the TIS describing how to machine the rotors. You can machine them down to the minimum thickness if you need to. You do however, need to ensure that both sides are evenly machined and the appropiate runout and surface finish specifications are maintained.

Should you machine your BMW rotors?
Generally speaking, BMW rotors are cheap enough where it does not make economic sense to turn them. Plus, replacing them guarantees you will have a rotor with the correct runout and surface finish criteria.

When do you have to replace your rotors?
When they are below the specified minimum thickness.

What if my rotors are at, but not below the minimum thickness?
Then you can use them again, but only for one more set of pads, assuming you are using OEM pads or pads with equal or less rotor wear than the OEM pads.

What's the theory behind the minimum thickness criteria?
When BMW selected the pads and designed the rotor thickness, it was not done randomly. The expected range of rotor and pad wear is known and designed on purpose.

Your pads have a wear sensor which goes off when you have 3mm or less pad material. It is a safe assumption that the pad wear sensor is designed to go off before you wear your rotors down so thin that they are hazardous. So the deduction from this is that the wear rate of rotors with OEM pads is 1.6mm or less per set of pads. Which in turn means the absolute safety limit of rotor thickness is probably about 18.8mm front and 15.8mm rear (for 323/325/328 - add 3mm for 330). To put it another way, the BMW rotors and pads are designed in such a way that if you reuse the rotors at minimum thickness, your pad wear sensor will go off before your rotors get too thin.

So do should I replace the rotors everytime I replace the pads?
Assuming they are at or above the minimum thickness for reuse and are otherwise within spec, it's up to you to strike the best balance of tradeoffs between performance and money. It is an absolute certainty that you will get better braking performance out of new rotors than reused rotors. But depending upon the condition of the rotors, the difference in performance may be slight.

The one thing you do NOT want to do however, is reuse rotors with a non-OEM brake pad of unknown wear rate. By doing so, you run a very serious risk of having a higher rotor wear rate than was intended by design. As a result, your rotors may become dangerously thin and even fail before the pad wear sensor goes off.
jpr is offline   Reply With Quote
Ads by Google

Guests, get your FREE E46Fanatics.com membership to remove this ad.
Old 03-24-2007, 07:51 PM   #2
jbeurotech
Regional Sponsor
 
Join Date: Aug 2006
Location: New Brighton MN
Posts: 5,018
My Ride: 2000 E46 with 254K
You forgot to have on there DO NOT TURN M rotors!
__________________

Seth Thorson
Service Manager/BMW Tech
JB Eurotech Service "Your Reasonable Dealer Alternative"

General Questions can be sent to appointment@jbeurotech.com

1. Do not argue with an idiot. He will drag you down to his level and beat you with experience.
2. Light travels faster than sound. This is why some people appear bright until you hear them speak.
jbeurotech is offline   Reply With Quote
Old 03-24-2007, 08:00 PM   #3
jpr
Registered User
 
Join Date: Aug 2005
Location: San Diego, CA
Posts: 3,005
My Ride: '99 323i
Didn't forget it, didn't know it.

Are you specifically refering to the ones with the floating disc design? I can see where that wouldn't work out very well.
jpr is offline   Reply With Quote
Old 03-24-2007, 08:03 PM   #4
jbeurotech
Regional Sponsor
 
Join Date: Aug 2006
Location: New Brighton MN
Posts: 5,018
My Ride: 2000 E46 with 254K
Look up M3 rotors it says right in TIS do not machine M rotors, weird huh I never rec machine any BMW rotors, I used two and have changed my mind after years of real world results with turning BMW rotors. Do a search on a thread where me and Alex323i had this discussion
__________________

Seth Thorson
Service Manager/BMW Tech
JB Eurotech Service "Your Reasonable Dealer Alternative"

General Questions can be sent to appointment@jbeurotech.com

1. Do not argue with an idiot. He will drag you down to his level and beat you with experience.
2. Light travels faster than sound. This is why some people appear bright until you hear them speak.
jbeurotech is offline   Reply With Quote
Old 03-24-2007, 08:22 PM   #5
flyinj3x
Registered User
 
flyinj3x's Avatar
 
Join Date: Nov 2006
Location: Maine
Posts: 1,828
My Ride: 03/03 330ci
Send a message via MSN to flyinj3x Send a message via Yahoo to flyinj3x
nice job jpr! great info as usual. i like how you included "BMW", "brake", and "rotor" in the title, shouldnt be missed on the search.
flyinj3x is offline   Reply With Quote
Old 03-24-2007, 08:22 PM   #6
jpr
Registered User
 
Join Date: Aug 2005
Location: San Diego, CA
Posts: 3,005
My Ride: '99 323i
Wierd -I'm running a somewhat elderly version (Dec 2000) of the TIS, which only covers the E46 M3 up to 2001, largely prior to it's USA debut. There is no such disclaimer on my version.

But back checking to the E36 M3, it is exactly there where you said it would be - "(M models may not be machined)"

So the two questions are -
(1) did the non-machining direction get included for the E46 M3 in a later version of the TIS?
(2) Why not? As noted above, my first guess would be that the real issue is the compound floating rotor design prevents accurate machining, but are there other considerations? And for that matter, did the E36 even use that design?

As I recall the thread you're refering to, I believe the conclusion was, yes you can machine the rotors, but it's to imagine the circumstances where it would be worth the bother (and expense).
jpr is offline   Reply With Quote
Old 03-24-2007, 08:31 PM   #7
flyinj3x
Registered User
 
flyinj3x's Avatar
 
Join Date: Nov 2006
Location: Maine
Posts: 1,828
My Ride: 03/03 330ci
Send a message via MSN to flyinj3x Send a message via Yahoo to flyinj3x
my TIS version 3.4.1 (NOV-2003) states the front or rear M3 rotors not be turned.

Last edited by flyinj3x; 03-24-2007 at 08:32 PM. Reason: fix
flyinj3x is offline   Reply With Quote
Old 03-25-2007, 11:01 AM   #8
jpr
Registered User
 
Join Date: Aug 2005
Location: San Diego, CA
Posts: 3,005
My Ride: '99 323i
Thanks for settling question 1.

Any ideas on question 2?
jpr is offline   Reply With Quote
Old 03-25-2007, 11:21 AM   #9
328ciNY
Registered User
 
Join Date: Dec 2006
Location: New York
Posts: 22
My Ride: 2000 BMW 328CI
Hey.. I thought this would be the right thread to ask since its about brakes/rotors. The auto places around here have nothing listed in inventory for brake pads OR rotors for a 2000 328CI (my car) but they DO HAVE brakes/rotors for the 325CI -- will these brake/rotors fit my car? When I search around for "e46 brakes" I see most brands fit ALL (323/325/328/330) but NOT M-series, so I assume the brake pads/rotors will fit from a smaller-engined 3 coupe?

Thanks for any help.
328ciNY is offline   Reply With Quote
Old 03-25-2007, 11:43 AM   #10
jpr
Registered User
 
Join Date: Aug 2005
Location: San Diego, CA
Posts: 3,005
My Ride: '99 323i
Rotors - the 323 and 330 have uniquely sized rotors, the rotors on the 325 and the 328 are the same.

Pads - the 323, 325, and 328 all use the same calipers and therefore all use the same pads. The 330 has different calipers and use different size pads.

The M3, is of course, it's own animal all the way around.
jpr is offline   Reply With Quote
Old 03-25-2007, 11:56 AM   #11
328ciNY
Registered User
 
Join Date: Dec 2006
Location: New York
Posts: 22
My Ride: 2000 BMW 328CI
Thanks for your response. So, any E46 328/325 rotors I could use (I guess that means .. 99 - 2005), and any E46 323/325/328 brake pads will work?

Thanks in advance!!
328ciNY is offline   Reply With Quote
Old 03-25-2007, 12:11 PM   #12
jpr
Registered User
 
Join Date: Aug 2005
Location: San Diego, CA
Posts: 3,005
My Ride: '99 323i
Quote:
Originally Posted by 328ciNY View Post
Thanks for your response. So, any E46 328/325 rotors I could use (I guess that means .. 99 - 2005), and any E46 323/325/328 brake pads will work?

Thanks in advance!!
correct
jpr is offline   Reply With Quote
Old 03-25-2007, 12:47 PM   #13
Commander FAT
Network Analyst
 
Join Date: Aug 2002
Location: Chicago
Posts: 3,484
My Ride: 2002 330Ci
Minimum disc thickness is stamped on the disc. No need to deduce anything.
__________________
Because the B isn't for bling.
Commander FAT is offline   Reply With Quote
Old 03-25-2007, 01:03 PM   #14
jpr
Registered User
 
Join Date: Aug 2005
Location: San Diego, CA
Posts: 3,005
My Ride: '99 323i
Quote:
Originally Posted by Commander FAT View Post
Minimum disc thickness is stamped on the disc. No need to deduce anything.
Yes- that would be the fact part, not the deduction part. It's also in the TIS and handy thing to know without having to look at your disc, say for example when your shop is on the phone trying to sell you new discs because at they are almost at the minimum thickness.
jpr is offline   Reply With Quote
Old 03-25-2007, 01:45 PM   #15
Commander FAT
Network Analyst
 
Join Date: Aug 2002
Location: Chicago
Posts: 3,484
My Ride: 2002 330Ci
Then why is deduced in paranteecees ( I can't spell that damn word)?
__________________
Because the B isn't for bling.
Commander FAT is offline   Reply With Quote
Old 03-25-2007, 01:56 PM   #16
jpr
Registered User
 
Join Date: Aug 2005
Location: San Diego, CA
Posts: 3,005
My Ride: '99 323i
Quote:
Originally Posted by Commander FAT View Post
Then why is deduced in paranteecees ( I can't spell that damn word)?
I listed the 330 rotor minimum thickness as deduced since, my version of the TIS predates the introduction of the 330 and does not have that info. The deduction is that they use the same designed rotor wear rate. IF you can confirm it, that would be helpful.
jpr is offline   Reply With Quote
Old 03-25-2007, 10:51 PM   #17
Rob Levinson * UUC Motorwerks
UUC Motorwerks, *******
 
Rob Levinson * UUC Motorwerks's Avatar
 
Join Date: Dec 1969
Location: GA
Posts: 3,969
My Ride: 7s, M5s, M3s, others
Quote:
Originally Posted by jpr View Post
And for that matter, did the E36 even use that design?
Just like the E46 M3, US versions pf the E36 M3 got 1-piece rotors and Euro got the floating design.

- Rob
__________________
- Rob Levinson * UUC Motorwerks * 678-679-5360 * uucmotorwerks.com

BIG BRAKE KIT HEADQUARTERS!

ALL CURRENT UUC SPECIALS:
-[ CLICK HERE ]
Rob Levinson * UUC Motorwerks is offline   Reply With Quote
Old 03-25-2007, 10:59 PM   #18
jpr
Registered User
 
Join Date: Aug 2005
Location: San Diego, CA
Posts: 3,005
My Ride: '99 323i
Quote:
Originally Posted by Rob Levinson * UUC Motorwerks View Post
Just like the E46 M3, US versions pf the E36 M3 got 1-piece rotors and Euro got the floating design.

- Rob
Does that include the ZCP rotors? Are the ZCP rotors the Euro/CSL version?

What do you make then of the proscription on machining the "M" rotors? Is the terms "M rotor" BMW code for floating rotor, or is there something special about even the 1 piece rotors that prevents them from being able to be machined?
jpr is offline   Reply With Quote
Old 03-26-2007, 09:57 AM   #19
jpr
Registered User
 
Join Date: Aug 2005
Location: San Diego, CA
Posts: 3,005
My Ride: '99 323i
Just to consolidate info, here's the E46 M3 rotor sizes -
M3 - 325x28 front, 328x20 rear
M3 optional drilled (ZCP) - 345x28 front, 328x20rear

I believe the minimum thickness would then be 26.4mm and 18.4mm, but it would be nice if someone could confirm this.
jpr is offline   Reply With Quote
Old 03-26-2007, 10:38 AM   #20
Rob Levinson * UUC Motorwerks
UUC Motorwerks, *******
 
Rob Levinson * UUC Motorwerks's Avatar
 
Join Date: Dec 1969
Location: GA
Posts: 3,969
My Ride: 7s, M5s, M3s, others
Quote:
Originally Posted by jpr View Post
Does that include the ZCP rotors? Are the ZCP rotors the Euro/CSL version?
Yes, the 345mm front rotors are identical to CSL rotors. The 325mm front rotors are standard M3 Euro. The 328mm rear are common to CSL/Competition Package/Euro.

Quote:
What do you make then of the proscription on machining the "M" rotors? Is the terms "M rotor" BMW code for floating rotor, or is there something special about even the 1 piece rotors that prevents them from being able to be machined?
I would think that it has to do with the same "commen sense" concept against machining any BMW rotor, that the allowable wear depth is very small... and considering that the Motorsport applications are expected to be used more aggressively and see higher heat ranges, it's simpy easier to say "Nein, machining verboten" than to say "Das machining ist für Dummköpfe!" and get into a whole discussion about it.

I suspect that the TIS uses "M rotor" to mean floating, but cannot substantiate that beyond a qualified guess.

- Rob
Rob Levinson * UUC Motorwerks is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Censor is ON





All times are GMT -5. The time now is 11:30 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
(c) 1999 - 2011 performanceIX Inc - privacy policy - terms of use