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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Suspension | Brakes | Chassis > M3 lower control arm (thrust arm?)



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      01-25-2020, 09:18 AM   #1
Vulcan50
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M3 lower control arm (thrust arm?)

I need to replace my lower control arms, is there any benefits to swapping to m3 arms? Assuming that I'm only swapping them?

I searched and only found information on swapping both upper and lower.
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      01-25-2020, 12:36 PM   #2
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I assume you mean the front suspension arms, and assuming that when you say lower control arm you mean the rearmost (of the front) ones?

There's definitely an advantage to replacing one, or the other, or both of them, compared with stock.

The front m3 arm ('radius rod') has a far firmer bushing at the inner end, which helps a lot with keeping the frond end and steering predictable. Otherwise the m3 rod is identical to the non-m arm.

The rear one ('wishbone') is slightly longer, as well as having a ball joint at the inner end rather than a rubber bushing. The extra length gives approximately 0.75deg less (more negative) camber, which aids front end grip a lot. The ball joint again firms up the front end.

So replace the radius rods and you make the biggest change to the bushing stiffness in the front suspension. Replace the wishbones and you gain a bit of front end grip (and a little stiffness). Replace both (all 4 arms) and you get all those advantages (at the cost of a tiny amount of NVH, but not much else).
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      01-25-2020, 03:03 PM   #3
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Thanks for the clarification.

2 more questions regarding just the lower. (this is my daily driver, autoX every once in a while.)

Is the difference significant?

Does it affect wheel fitment? How about with upper and lower?
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      01-25-2020, 03:33 PM   #4
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Quote:
Originally Posted by Vulcan50 View Post
Is the difference significant? Yes, but doesn't harm daily duties at all, in my opinion.

Does it affect wheel fitment? Yes. How much? Some.

How about with upper and lower? Indifferent to just replacing the lower, in terms of wheel fitment, because the arms are identical except the bushing.
.
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      01-25-2020, 10:15 PM   #5
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Awesome, thanks.

One final question, is it necessary replace the linkage for the headlight thing?
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      01-26-2020, 01:54 AM   #6
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I'm not sure. Check on realoem to see if the m3 and non-m part numbers match. I think it does need to be replaced.
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      01-26-2020, 07:37 PM   #7
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Just get the M3 front control arm set and be done with it. You will absolutely be amazed.
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      01-31-2020, 10:55 PM   #8
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So I'm pretty much set on doing upper and lower while I'm in there. What will that do to my wheel fitment?
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      02-01-2020, 02:06 AM   #9
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It'll move the wheels outwards by ~10mm, and forwards a little. Sorry, I haven't measured that.
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      02-01-2020, 08:39 PM   #10
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Quote:
Originally Posted by Tambohamilton View Post
It'll move the wheels outwards by ~10mm, and forwards a little. Sorry, I haven't measured that.
What do you mean forward? Shouldn't the center remain centered front to back in the wheel well?
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      02-01-2020, 10:51 PM   #11
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It's a subtle minor upgrade, worth doing if you're replacing the parts anyway as the cost is about the same.

Only time I'd say you might not want them, is if you're using low profile runflats, as you'd just be making already the rough ride a little worse. And if you're using runflats you're not getting much of a sports car level of handling anyway lol.
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      02-02-2020, 01:41 AM   #12
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Quote:
Originally Posted by Vulcan50 View Post
What do you mean forward? Shouldn't the center remain centered front to back in the wheel well?
It can't. Front arm is the same length, subframe is unchanged, rear arm is longer...the wheel must move forward. Increases KPI a little.
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      02-07-2020, 12:17 AM   #13
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Quote:
Originally Posted by Tambohamilton View Post
Quote:
Originally Posted by Vulcan50 View Post
What do you mean forward? Shouldn't the center remain centered front to back in the wheel well?
It can't. Front arm is the same length, subframe is unchanged, rear arm is longer...the wheel must move forward. Increases KPI a little.
I want to clarify that I'm wondering does the wheel come forward when doing both upper and lower? I get that it would move when only doing one.
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      02-07-2020, 01:29 AM   #14
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The front arms (non-M and M3) are both the same length, the rear M3 arm is longer. So it doesn't matter if you change the front arm or not; the geometry effect is the same from changing the rear arm alone, or changing both.
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      02-08-2020, 09:06 AM   #15
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Quote:
Originally Posted by Tambohamilton View Post
The front arms (non-M and M3) are both the same length, the rear M3 arm is longer. So it doesn't matter if you change the front arm or not; the geometry effect is the same from changing the rear arm alone, or changing both.
Interesting. So does the m3 wheel sit off center in the wheel well? Or are the body panels different to basically push the wheel well forward?
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      02-08-2020, 09:08 AM   #16
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99% sure it's different panels on the M3. Not sure you'd notice the offset, visually
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      02-22-2020, 08:44 AM   #17
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Awesome, interesting
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      02-22-2020, 09:48 AM   #18
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The M3 control arms in the front have a natural .75 camber. OEM does not. The bushings in the M3 control arms are stiffer. This creates a much more stiffer feel at the steering wheel. Thus, you feel even more connected to the road.

My advice would be to wait until the 11 piece version comes on sale, if time is not of the essence, and put the M3 control arms in the both the front & rear. FCP will give you a lifetime warranty & on sale it's $650.00 or so.
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      02-23-2020, 03:51 PM   #19
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Quote:
Originally Posted by mweisdorfer View Post
The M3 control arms in the front have a natural .75 camber. OEM does not. The bushings in the M3 control arms are stiffer. This creates a much more stiffer feel at the steering wheel. Thus, you feel even more connected to the road.
.
My alignment is getting done tomorrow, but since I installed the front and rear arms on Friday, the steering is so loose and jerky... I pray the alignment corrects this...
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      02-23-2020, 06:14 PM   #20
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Quote:
Originally Posted by Wingnutts View Post
Quote:
Originally Posted by mweisdorfer View Post
The M3 control arms in the front have a natural .75 camber. OEM does not. The bushings in the M3 control arms are stiffer. This creates a much more stiffer feel at the steering wheel. Thus, you feel even more connected to the road.
.
My alignment is getting done tomorrow, but since I installed the front and rear arms on Friday, the steering is so loose and jerky... I pray the alignment corrects this...
It will
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      04-02-2020, 06:49 AM   #21
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Quote:
Originally Posted by Wingnutts View Post
My alignment is getting done tomorrow, but since I installed the front and rear arms on Friday, the steering is so loose and jerky... I pray the alignment corrects this...
So did the alignment solved it?
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      04-02-2020, 09:21 AM   #22
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Quote:
Originally Posted by Dovydas.B View Post
So did the alignment solved it?
My apologies, I thought I responded to this. After 2 trips to the alignment shop due to frozen eccentric bolts in the rear, and then having a fellow BMW owner at the shop work on it, the steering wheel is perfectly centered, the steering is extremely tight and is a noticeable improvement over my stock 85,000 miles arms and bushings. If you sneeze on the highway, you'll be on the side of the road at 60 mph + though. Mexico speeds are very, very sensitive, but it does not wander at all.
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