So you bought your BMW because it is billed as "The Ultimate Driving Machine". From the factory, BMW had several options on sway bars depending on your model. Sizes for them ranged between 18.5-24mm front diameter bars and 15-21mm rear bars depending on body style and year. Generally the 330's had the largest bars and as a general rule the thicker the bar, the more stable the car during aggressive driving. But it isn't as simple as "bigger bars are better".
What is important to remember is that the front and rear bars work in tandem, and small changes to either can have a drastic difference in the way your car handles. For instance, the Dinan performance sway bars for the E46 are much smaller diameter in comparison to my UUC Swaybarbarians and are set to add a little extra oversteer to the dramatic understeer your BMW has from the factory. It isn't a great deal of difference over factory sport sway bars and I can only figure this is because Dinan is a factory BMW performance division and they want it to be "aggressive" but still keep you from killing yourself. And since this topic is so broad and the range of changes and options is so great I will move on and discuss my personal findings and experience.
I got a used set of UUC swaybarbarians for the E46. It was an INSTANT and DRAMATIC change (intially I set the bars to their stiffest setting front and rear). All of a sudden my car felt like it was going to go where I pointed it and NO body roll whatsoever. It almost felt too "twitchy" and I admit, at first, I was a little scared of it. The tail end noticeably swept around much better. If my venerable little 323 motor had enough oomph, the car could be steered with the gas pedal. After a few weeks of driving it like this I became accustomed to the way it felt and began to push my car harder and harder. I then started playing with the different settings and I began to learn by FEEL how and what the car does. This is probably one of the more exciting things I have leared in my time as a "Bimmerhead" and I am loving it.
Here are a few pointers for those thinking about sway bars:
- Get adjustable sway bars. Non adjustable sways would be boring and if you are paying upwards of $400, why not get something that allows you to make adjustments to fine tune the car to YOUR style?
- Buy heavy duty adjustable front sway end links. You will kill your stock one's in short order if you don't and it makes a world of difference in feel and allows for even more fine tuning of your car.
- Beef up your rear sway bar mount tabs. The BMW stock tabs on the rear are very weak and thin. Running a super fat, stiff bar like the UUC's, it is possible you could tear them. Turnermotorsport.com has a set of weld in reinforcements that cost $20 and you can probably get them welded in by a muffler shop for under $50. It is worth it. Keeping them from breaking is so much easier than fixing them when they are broken.
- Stiffer isn't always better. You'll see what I mean when you get them!
- Finally, GET SOME NEW SWAY BARS! It is the best mod I have ever done.