click the link:
http://www.realoem.com/bmw/select.do
enter your vehicle information and you should get the following results for OEM (depending on the current OEM wheel set up):
2 LIGHT ALLOY RIM 8JX18 ET:47
02 LIGHT ALLOY RIM 81/2JX18 ET:50
thus a high offset is good for your vehicle (+40s)...to really know for sure...compare the above offsets to the new offsets at this link to determine the clearance:
http://www.1010tires.com/WheelOffsetCalculator.asp