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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Suspension | Brakes | Chassis > Another 'M3 suspension on non-M...' thread



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      05-21-2019, 04:59 PM   #1
Tambohamilton
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Question Another 'M3 suspension on non-M...' thread

So I've done a bunch of reading and searching, and I have a few questions still about the M3 parts which fit on non-M cars...

At the front end, the M3 'radius rods' (front arm) are the same length as the non-M parts, but have a stiffer bushing, right? But the M3 wishbones (rear arm) are longer, so they add about 0.75deg of negative camber. My question here is, does fitting the M3 wishbones (and radius rods, since they seem to be the same length as the standard parts) also move the front wheels forward slightly from their standard position, adding caster? If it doesn't, what makes up for the length discrepancy?

At the back end, the M3 has a different subframe, and mainly aluminium arms. But the only arm which is a different length from the non-M items is the track control arm (rearmost one)? I've read on a 1er forum that all others are functionally the same (or actually the same, in the case of the trailing arm), with the exception of one ball joint in the place of a rubber bushing on one of the arms. But then, I've also read that the lower wishbone ('roll-over strut') is longer on the M3, which contributes to increased negative camber when fitted to a non-M car... Which is it?

Finally, does anyone have a set of solid rear subframe mounts lying about that they could take some accurate measurements of, please? I really just need the OD of the mounts themselves - I can get the rest from my car before I take it apart.

Thanks for your help!

Last edited by Tambohamilton; 05-21-2019 at 05:01 PM.. Reason: Typos
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      05-22-2019, 02:52 PM   #2
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The front arms are LONGER for extra camber and have a stiffer bushing for improved steering response with a little more NVH.

As for the rear I think you got it a little backwards. Start by checking out this pic of my rear subframe once I had bolted all my M3 stuff to it. There are two control arms that are part of the M3 suspension. IIRC only the top most one is shorter for extra camber.

https://drive.google.com/file/d/0B8p...ew?usp=sharing
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      05-22-2019, 05:47 PM   #3
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So both M3 front arms are longer than the non-M ones? I haven't seen that mentioned anywhere before, but it makes sense. Everything I've read only mentions swapping the wishbones to change camber; not necessarily swapping the radius rods to suit (though you'd be daft not to, given the bushings in the non-M parts!).

So what you're saying is the M3 rear upper 'wishbones' are shorter than the non-M ones, the 2 lower arms are the same length as the non-M ones? And the track control arms are different to suit the differing subframes. I see. Roughly how much negative camber did you gain by swapping the wishbones? And I guess you swapped the upper control arms because they have a ball joint in place of a rubber bushing?

Are those M3 subframe bushings you used? You didn't feel the urge to get a bore gauge out and measure the diameters of the subframe mounts before you pressed them in, no??
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      05-25-2019, 11:11 AM   #4
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You are correct, front bottom is longer. Top is same size. Affects the geometry. Camber and caster too. One can't change without affecting the other.

On the rear only the toe link is longer. All the rest are same. It has been seintificalyscientificly proven that rear m3 parts aren't an upgrade. Check 1addict forum.
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      05-26-2019, 04:41 AM   #5
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Thanks for confirming. Has anyone measured how much the caster changes when the M front wishbone is installed? Anyone had any issue with wheel rub because of it too?

Yeah, I've read Fer1x's thread on 1addicts...I really want to know what he does for a living; how he has that much spare time, that equipment and those skills. I found it super interesting that he measured the stiffness of the rubber bushes and the ball joints, and decided there wouldn't be a noticeable difference between them for the one arm which has 2 ball joints instead of 1 of each.

Anyone know what the effect of the different toe arm geometry is on the M cars?
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      05-26-2019, 05:21 PM   #6
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With increases caster steering becomes more stiffer , better high speed stability, better during braking in corners, gives more negative camber durning cornering and etc.

Rear toe link is longer because the subframe is diferent and is enginered like to to make the rear end more complaint because it will have more levearage to eliminate unwanted toe changes during aggressive driving.
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      05-27-2019, 01:45 AM   #7
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More leverage? So the knuckle is different too?
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      05-27-2019, 05:28 PM   #8
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The knuckle is different too with diferent mounting tabs for the brake carrier. I think I confused you. Non M link is longer. M is shorter. Shorter lenght here equals to less travel up and down. Or so I think. The difference is where the link is attached on the subframe. It's on the same line with the lower control arm. Non M mounts further in towards the diff.
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      05-27-2019, 06:26 PM   #9
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OK, thanks. So I guess that having the M toe link pivoting in line with the lower control arm, there should be less variation in toe through the suspension travel?
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      05-29-2019, 02:04 AM   #10
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Quote:
Originally Posted by feuer View Post
It has been seintificalyscientificly proven that rear m3 parts aren't an upgrade. Check 1addict forum.
Do you mean this thread: https://www.1addicts.com/forums/show....php?t=1079383

Are the M3 guide rods an upgrade? They replace a bushing with a bearing

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      05-29-2019, 08:56 AM   #11
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Quote:
Originally Posted by freedomfries View Post
Do you mean this thread: https://www.1addicts.com/forums/show....php?t=1079383

Are the M3 guide rods an upgrade? They replace a bushing with a bearing

Yep, but in the same thread he measures and compares radial bushing stiffness vs ball joint stiffness, and decides there's not enough difference to be noticeable...especially when it's only one out of many joints which is different (excluding the incompatible M3 toe arm).
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      05-29-2019, 09:39 AM   #12
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Quote:
Originally Posted by Volasko View Post
The front arms are LONGER for extra camber and have a stiffer bushing for improved steering response with a little more NVH.

As for the rear I think you got it a little backwards. Start by checking out this pic of my rear subframe once I had bolted all my M3 stuff to it. There are two control arms that are part of the M3 suspension. IIRC only the top most one is shorter for extra camber.

https://drive.google.com/file/d/0B8p...ew?usp=sharing
He actually had it right. Not sure what you're talking about here... Rear M3 toe arm is longer. That is th eonly length difference in the rear. Front camber arm is longer. That is the only length difference in the front.

The front arm pushes the bottom of the wheel OUT (adding camber). The top of the wheel pivots IN. The camber arm isn't at the dead center bottom of the knuckle so the toe also changes. The toe change gets dialed back out with tie-rod end adjustment. I don't think caster changes much if at all.
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      05-29-2019, 09:45 AM   #13
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Quote:
Originally Posted by Tambohamilton View Post
OK, thanks. So I guess that having the M toe link pivoting in line with the lower control arm, there should be less variation in toe through the suspension travel?
There is definitely some change to the rear wheels dynamic motion ratio, but, no one has 3D modeled the suspension of both cars to show the difference. Felix is working on that now I believe. A modified car may significantly change the affect of changing the toe arm length and pickup point so it's a difficult question to give a definitive answer to. Lowering the car 1" might change the affect from a positive one to a negative one for example... or vice versa.
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      05-29-2019, 11:29 AM   #14
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Awesome. I'd model it myself if I had anywhere near the free time...sadly not! Glad someone else can. Thanks for the response.
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      05-29-2019, 12:25 PM   #15
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Not sure if all that smart talk is helping. The
Only real thing that's matters is ur going to love way way ur car handles. Well worth the upgrades
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      05-29-2019, 06:38 PM   #16
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Sure, but if you could get to the same place for cheaper, then that's the biggest win! At least that's what I'm hoping for, since I don't have much money...
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