I'm not the first owner of this car, so I don't know if these were the original wheels but I assume so (given there are no mods anywhere else on the car it seems quite likely nobody has fiddled with it so far), but despite scouring resources like bmwstylewheels.com I haven't found what looks like a match..
They're 18"s (currently running 245/45R18 all round, non-staggered wheels):
(Click for the full size photo)
This is mostly idle curiosity with a side off don't-want-to-take-them-off-to-check-the-offset-because-I'm-lazy.. while I peruse wheel options