[mweisdorfer]

Originally Posted by Steve Sas

Aren't the rear M3 control arms stronger than the 335i ones?
And lighter as well??

Lighter yes. Stronger? Debatable

[mebespencer]

A little late to this thread, but if OP went with the 5-piece kit (as I did back when I installed these) then I highly recommend the Whiteline RSFB Insert kit. FCP had them for just under 50 bucks when I ordered last week, install is a little annoying but nothing difficult, and they do to the rear of the car what these M3 arms do to the front.

I ran the M3 arms alone for the better part of a year, and the rear of the car felt "out of phase" with the front. What I mean by this is that whenever the front would respond to a steering input, the rear took half a second longer to exhibit the same response. It felt pretty floaty and a little unpredictable, particularly in quick transient inputs like you'd find in a chicane. This front-to-rear inconsistency really lowered my confidence in the car, and while I definitely had decent mechanical grip from my coilovers and tires I just simply didn't feel safe whipping into a corner abruptly from a straight line.

In come the Whiteline subframe inserts: they absolutely reeled the rear end back in, for a fifth of the price of the control arms up front. The car feels so much more like my friend's E92 M3, where quick inputs (especially at speed) are met with an immediate load-up on both axles at the same time. The feel of the car after installing these is pretty much exactly what I was looking for, and I think you'll probably come to the same conclusion yourself.

Just my 2 cents...