Can anyone explain what 'OFFSET' means regarding the alloy wheels? I have an X5 and have read on some website that not all alloy wheels fit these cars, although many people buy any alloys and then have problems. The 3 parameters that are essential are: studs- 5, stud diameter- 120 and Offset- 50 (according to that website). Now if you enter ebay and look for alloys you get offset 34, 40 or 50. Is this offtes really that importanat?