I currently have 225/40 18 (SO3's) on a 18 x 8.5 rim up front with 285/30 out back on 18 x 10 rims. The rear traction is great, but the front feels like it needs a little more grip. It's a street car primarily, but driven aggresively.

Just curious if I can go a little wider on the same rim for better balance with no rubbing.

 

In terms of wheel width, a 245 on an 8.5 inch wheel is just about perfect. The challenge will be finding something suitable with the correct O.D., like a 245/35-18. The rubbing issue is dependant upon the wheel offset. I have 275s on 10s on the front of my car, albeit with lots of negative camber and rolled lips, but this should illustrate the possibilities.

 

I'm running with 245/35 18 (Pirelli PZero Asimmetrico) on the front and 285/30 18 on the back. No rubbing problems. Front rim width measures around 9.5 inches.