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      12-22-2012, 10:56 PM   #1
BMWM.D.
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Drives: E90 335i & C6 Grand Sport
Join Date: May 2009
Location: Santa Barbara

Posts: 684
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Results: M3 front control arm/wishbone upgrade (no tension struts)

This has probably been done and covered before, but I figured I'd share my results for anyone considering changing to any M3 suspension parts. Here it goes....

I personally aligned my E90 335i about a month ago on our brand new Hunter/BMW KDS alignment machine. The car has under 25k miles and everything looked as it should, so I set the rear camber and front/rear toe to BMW's specifications:

rear camber: -1 50' (1 degree & 50 minutes)
rear toe: 18'
front toe: 14'
Caster (not adjustable) : 7 05' / 7 00'

What I didn't like was my front camber:

left: - 14' (-.23 degrees)
right: -31' (-.51 degrees)

That's right around 1/4 degree negative on the left and 1/2 degree negative on the right for you guys that don't use the minute system. This is my second E90 335i, and the first one I had (same year/model) started showing wear on the outside shoulders of the front tires. There were actually almost bald when I traded that car in with only 17k miles. The rest of the tire looked great.

Anyway, I decided I wanted some more negative camber on this car. Besides possibly evening out the front tire wear for the way I drive, it should improve front end grip and reduce understeer. I see that as win-win. Since I don't like removing the strut locating pin to make adjustments, I decided to try the M3 control arms, or wishbones as BMW calls them.

Since I really don't have any complaints with the ride quality and handling of this car, I decided to not replace the tension struts -- just the 2 lower front control arms and the needed headlight sensor link. The install was very quick and I'm quite happy with how it came out. Since I had just aligned this car on this same alignment machine about a month ago, I think I got a very accurate idea of what should be gained by just changing these arms.

Results:

First, let me say that doing this threw my front toe MAJORLY out of whack. It was bad just driving it through the shop to the alignment bay. The tires were scrubbing badly and the steering was horrible. The total front toe was almost +6 degrees before I made my adjustments, so be very careful if planning to drive the car prior to alignment.

Anyway, here were the final numbers:
camber
left: - 47' (-.78 degrees)
right: - 53' (-.88 degrees)

caster
left: 7 31' (7.51 degrees)
right: 7 27' (7.45 degrees)

So I gained a around a half a degree of negative camber and an extra ~half degree of caster. The strut pins were not removed. Not only did I get the results I was hoping for, but it seemed to even out my cross-camber readings without needing any adjustments to the strut mounting. I haven't noticed any difference in ride quality, but the car does seem more stable at freeway speeds -- probably from the caster gain. Besides a little more toe-in both front and rear, the car is very close to E90 M3 specifications.

I think the conclusion here is that the M3 control arms (wishbones) are what's responsible for the camber and most of the caster changes on these M3 control arm upgrades. I will probably change the tension struts in the future when my run-flats wear out, but for now I don't want any added stiffness or vibration. For the minimal cost, I think this is a great upgrade.
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