328i wheel sizes ?

[Choppers]

I've just bought a 328i Sport & have unfortunately just found out that the offside rear alloy needs replacing as its been welded at some point & the wheel is now leaking air (its the standard 17 inch split rim). I understand that the rear has slightly wider wheels than the front but I can't find the sizes anywhere. Does anyone know the difference between the rear & front ? or is it just the tyre size that is different ? Cheers for any help