225/40/18 is the size you want. They won't rub and they look great. Plus it's a pretty common size so you have lots of choices and they are cheaper than other sizes.
I had 225/40/18 on my ms3 wheels when I still had them on my 09 mz3. They'll fit better than the OEM 215/45/18s that come on ms3 wheels. They rubbed a bit at full lock on my car.