Most versatile wheel size, staggered or square?

[Jimminy]

Im half expecting to want to change wheels when I get a Z4C 3.0 si

I am more interested in performace than looks. The best options seem to be 225,45,17 all round or 225,40,18 all round.
It looks like there is more choice in 18 inch tyres so im leaning that way at the moment.

Are their other options i should be considering?

 

[cj10jeeper]

I suppose from a pure mechanical performance perspective the 17's would be best as they have less weigh, less rotational mass away from the centre, etc. but from an aesthetics perspective they look crap and the performance difference from them to 18's would be miniscule on a 3.0

I'd therefore find some light 18's.

 

[Jimminy]

If I went for a square set up, am I right in thinking I would need a 30 mm spacer on the back? Are there any downsides to that? Some Z4's came with the same size wheels front and back, did bmw fit a spacer or did they do something different?

 

[cj10jeeper]

BMW never fitted spacers to the rears. They used the same rims all round.

Personally to talk performance and then spaces is a contradiction. You may as well go for the oem staggered set up, get more rubber on the road and remove the weak link of spacers in the set up.