From what you have said I imagine your car has one of the standard staggered 18" options like 108s, MV2s, 107s, etc.
If so they wil be 8Jx18 ET47 fronts and 8.5Jx18 ET50 rears.
But people have fitted all sorts of alternatives in differing sizes and offsets! This thread might be a good starting point:- https://z4-forum.com/forum/viewtopic.php?f=49&t=107556