Originally Posted by NokTurNaL 330i
I run 255/40 17" on 9.5 rims square and it adds a ton of grip and improves breaking. Handling is improved also obviously. The 8.5 rim is small for this tire. You will notice that the tire will bubble on the side since the rim is narrow. You really need 9.0 or ideally 9.5 rim to provide the maximum support for the tire to handle vehicle weight and transient responses. Your steering feel will not be impacted that much if the tire has required support from the rim. Your M3 arms help also. If you get lightweight rims you will improve handling and braking by decreasing unsprung weight. You will definitely feel it. This is the best mod for these cars beside suspension.
Just my 2c ...
thanks for the comments. Good to know about the tire width vs wheel width. I suppose I could also consider 245 on 8.5?
Like your lightweight wheel angle. If I had the cash....