I'd like to stiffen my ride (2006 330Ci ZHP, 6m) before next year's track season. Here's what BMW has to say about its performance control arm package: "With a tighter, sportier feeling, the inclusion of a BMW Performance control arm with stiffer bushings gives your 3 Series an almost instinctual feel for the road. With adjusted spring rates and bushings, roll is drastically reduced, creating cat-like quickness, increased responsiveness, and stunning agility. Flexing with the motion of your vehicle around even the tightest curves, a BMW Performance control arm means athletic handling, faster turn-ins, and a totally immediate and much more intense reaction to the tarmac. It delivers a perfect compromise between racing car performance and driving comfort." Ya, put me down for some of that. Reduced roll and "cat-like" quickness. But since I don't really understand how a control arm does all that I'm wondering who among you has replaced control arms and what the outcome has been. Conceptually I can see how struts, springs and/or a strut brace stiffens suspension. Control arms? Not so much.
It's all marketing crap. The "Performance" control arms are exactly the same control arms that come stock on all ZHP package cars...they're just trying to hype these things up to sell to non-ZHP owners. As you guessed, control arms have essentially nothing to do with body roll, and they do not "drastically reduce body roll" by themselves...note that it says "With adjusted spring rates and bushings." Of course those "adjusted spring rates and bushings" are just the ZHP package stuff they are referring to anyway. The thrust bushings on my ZHP control arms were shot by 50k miles, so you ought to check those out. I ended up just replacing the whole control arm since the dealer good-willed the repair, but I was going to just put in new bushings. I also changed out the RTABs at the same mileage for what its worth.
