http://www.m3forum.net/m3forum/showt...hlight=E9x+18s
The stock tyres from the E92 M3 won't work obviously, to stick with the stock sizing you'd want to run either:
Front: 235/40/18 or 245/40/18
Rear 265/35/18
To retain within a 1% rolling difference.
I've actually just picked up a set of these today - gonna give it a try

way more tyre choices with 18s.