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Tech: rear susp difference -- Z3 vs M

6062 Views 9 Replies 5 Participants Last post by  Daver
Ok pro's ... perhaps someone with an ETK can answer my question:

The Z3 and M have very similar rear suspensions, but there is some difference because the wheel offsets are different. What accounts for this?

Different rear sub-frame?
Different trailing arms?
Different hub assemblies?

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Pretty deductive

Different rear sub-frame?
Different trailing arms?
Different hub assemblies?
(part of trailing arm)

The axleshafts are shorter (and with smaller flanges at differential)
Differential is different, and with larger finned cover
Spring/shocks are stiffer.
Brakes are vented/larger

I actually did look up the part numbers some months back to verify that the XMBR & trailing arms were different.



Great info! I'm curious as to why BMW chose to use two different configurations between the M cars and the Z3's. The only thing that comes to mind is that the Z3 configuration allows you to run identical rims front and back ... lower cost there, I suppose.

With the M setup, you run a rim with a more neutral offset ... I know on FWD cars that they run extreme offsets to try and counter torque steer as much as possible. I suppose there could be a drive-advantage for the M ... shorter axle shafts, more even load on the bearings... plus the deep offset rims look way cool :D

Thanks for the info and picture!
the suspension and everything is different because of the increased power and need for greater stability.. BMW M not only beefs up the engine but they do a considerable amount of work on upgrading the braking, suspension, and the things that are necessary to keep the car on the road... most people dont notice.. the different front and rear facias... gills, and flared out fenders in the rear.... wider tires mean better grip and performance
I belive there are even differences in the S52 and S54 M Roadster suspensions. I thougt I read somewhere that they lowered the ride about 1" for the S54. Anyone aware of any differences?
This is what I know...

The published data about the S-54 Rdstr suspension claims that it has the same calibration as the (then existing) M Coupe.
That is to say, that the springs and shocks are firmer.
That I believe to be true.

As for the ride height, it was most assuredly not lowered. Not the one I have anyway!
When parked next to the 99, it sat (past tense...) at an inch or more higher.

Last winter I installed double adjustable Konis on the 01. Instead of cutting open the 01's front struts (with 3000 miles on them), I swapped the parts from the 01 to the 99 (with 34,000 miles), and used the 99's struts for the Koni inserts. Nice that both cars wound up getting improved suspension out of the deal.


So much for what those 'experts' in those car magazines report. But then, we already knew that when we saw about 5 different 0-60 specs (over a WIDE range)on the S54 roadster. :dunno:

Hey Randy - Since we're on suspension, what's your opinion on leaving shipping blocks in the springs?

(While at the dealer for the 1200 mile service, I had them check for them and they said none were left in my car)
I was following your thread on Roadfly...

I wouldn't leave them in my car. If left in, they would effectively shorten the spring (the bump stop rubber comes into play sooner).

Besides, from what I've seen of them in pictures, the shipping spacers are not secured and can become dislodged causing eratic suspension response.
Since we're on suspension, what's your opinion on leaving shipping blocks in the springs?

Here is an excellent site which talks about the M Coupe/roadster rear suspension in great detail. Theoretically, you could upgrade your Z3 Coupe 3.0i to the M geometry without too much difficulty. The site lists part numbers and retail pricing of the parts.

Thanks for the pointer, Jedi... but I am currently looking to trade my 2001 Z3 Coupe for a 2002 M-Coupe... but unless I can find just what I'm looking for, I will keep my Z3 and still be happy.

I was curious about the differences just because I've spent so much time under Z3's, and hadn't had the same opportunity to work on M's. I knew there were differences in geometry, brakes and drivetrain, just wasn't sure to what extent the subframe and trailing-arms differed.
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