[gumba]

I run 215/50/15's on 8" rims (measures the same as a 225) and 335/35/15's on 13" rims on my 935DP. Tires are Michelin TB15. Fairly aggressive on the street, but no where near the limit, works fine. I also ran the 215's on a 9" rim with no issues. The front shocks are re-valved Bilsteins by SmartRacing which made a much better progressive shock. You could also play with the front/rear sway bar settings to dial out some of the under steer if you experienced it.
On our '75 iroc race car I used 245 fronts and either 295 or 315 rear Hoosiers.
I found a 1" wider rim lowers the tire diameter by 1/2".