Now that I've had some time to drive the car with the M3 bits (front control arms, front and rear sway bars, and rear subframe bushings) attached, I can give some feedback about how it is to drive.The first thing I noticed -- and continue to notice -- is the steering effort is higher. It's been a while since I drove an E90 M3, but I don't remember the steering being so tight on that car. I'm not sure if this is a side effect of the 335i's narrower track, or of the revised front end alignment (more camber and caster), or both. But it's significant. It's not exactly bad, and there's still plenty of feel, but I definitely have to use more effort on the wheel, especially on-center.
The second-most-significant change is the the back end of the car feels far more planted and secure than it used to. The stock suspension, although comfortable, always gave me a feeling of being a little floaty in the back, especially in throttle transitions and/or during cornering. Now it's very planted, with none of the float I used to perceive. The tradeoff is that it's a firmer ride back there now -- rear seat passengers could detect the different if they jumped from a stock car into a modified one.
Finally, the whole car corners flatter, thanks to the stiffer sway bars, and the front grip is improved, thanks to the increased front camber and the stiffer bushings in the control arms. It seems like it's impossible to un-stick the front end on the street. In fact, overall grip is high enough now that the only time I get the car to slide around is under power with the tires spinning.
Overall I'm delighted by the change the M3 components make to the suspension. It's still a perfectly comfortable car to use every day, but it is SO much more confidence-inspiring in the corners. If you've been thinking about these parts, do it now!
