Welcome to the Werkz.
Have a look at this site to find the details of your current wheels. Felgen-Katalog - BMW-Treff - der Treffpunkt für alle BMW-Fans und -Fahrer
, once you have that information look at the details of the rims that you are considering. You'll probably find that your current offset is around the +20 figure. If you vary too much from this you'll most likely hit issues with the width of the rim and/or tires. I went from 235/60/16 tire on a 16x7.5 +20 rim, to a staggered 245/45/19 & 275/40/19 on 19x9/10 +24 setup without any issues, although there isn't a real lot of extra room left.
Another useful site that I used to research what would fit is Wheel-Tire size comparer - WWW.RIMSNTIRES.COM
, it lets you fiddle around with the rim size, offset and tire sizes and then tells you what the changes are relative to the default tire that you have. Good luck with it all. Have a look at this earlier thread for the before and after shots of what I went through if you can be bothered. http://http://www.bimmerwerkz.com/fo...s-67291-3.html