thanks for that mD , i did some digging myself and could not find the bore size although it seems that bmw use only 72.56 or 74.1 these days with the bigger bore on E70 and M5 so i`ll assume that E53 and E83 are the same size .
our X3 is running 8x17 ET:46 style 148 rims with 235/55R17 ice tyres . i have X5 rims 7.5x17 ET:40 style 57 with 235/65R17 M+S michelin mxv.
the x5 rim will have more inner clearance and the same outer position as x3 rims .
i realise the x5 tyres will raise car 1 inch and cause speedo error but when i used 1010 tires.com calculator it said the larger profile tyre could cause brake failure .
i assume this is a standard warning in case one was only fitting one odd size tyre because i read on this forum of a few people fitting sets of larger profile tyres with no problems other than speedo error and even that can be corrected by a visit to dealer to re-addapt speedo values.
just a wee edit to say that the wheel bolts on E53 & E83 have the same thread pattern but the bolt seat & bolt head are different so use correct bolts for the wheels .