The first thing to consider is which wheels you are looking at? This is first before thinking about spacers and tyre.
The tyre sizes you are looking at are not quite correct for a Z3.
With a BMW oem staggered fitment which is
Front 7.5j et41 with rear 8.5j et41. 225/45/17with 245/40/17 tyres.
This setup requires no front spacer. The rear can easily take 20mm and probably more to get a nicer stance should you wish.
Got other wheels in mind with different fit? Post em up.
Scooblitz
The tyre sizes you are looking at are not quite correct for a Z3.
With a BMW oem staggered fitment which is
Front 7.5j et41 with rear 8.5j et41. 225/45/17with 245/40/17 tyres.
This setup requires no front spacer. The rear can easily take 20mm and probably more to get a nicer stance should you wish.
Got other wheels in mind with different fit? Post em up.
Scooblitz