A great article by TMS... copied from
http://www.turnermotorsport.com/html...cer_tech.shtml
This is a thread that we've been thinking of for a long time. We also created
a page on our website with the same information (more to come!). It consists of everything Turner Motorsport has learned about wheel spacers for BMWs. A lot of this info also applies to other makes as well. It's a very long and comprehensive collection of data, tips, and technical info and it's a bit Turner-centric but should prove useful to everyone. If you should have any further questions, please call or e-mail us.
Why Use Wheel Spacers?- Appearance. You want to push the wheels out for a better stance and more aggressive look. This is totally subjective to your personal tastes. And we can't tell you what to like...
- Clearance. Many wheels are not compatible with big brake kits. The spoke of the wheel will scrape the new brake caliper and you need a wheel spacer to push the wheel spoke away from the caliper.
- Correction. You may have bought a set of wheels that don't have the correct offset for your car. The offset may be too high, resulting in the wheels sitting too far inward. This is both ugly and incorrect as the tire can now rub on the inside wheel well, or on suspension components, etc. A wheel spacer will push the wheel out and 'correct' the offset.
- Handling. By spacing the wheels further apart, you can make the car more stable and corner better. You can gain a similar effect as adding a wider wheel without the added weight and expense.
Once you know WHY you need spacers, you can figure out what size to use...