I am running 225/45-17 on stock wheels, no problem whatsoever. You could run 235/40-17 on stock wheels, but they are really recommended for 7.5" or wider rims. As far as handling goes, without compromising comfort, I have settled fro Pirelli Pzero AS+, which for the Forte is a bit overkill, but I'm amazed how much more precise I steer through quick bends, where before, on the stock Nexen CP671 I corrected a lot. Also, the speedo difference to 215/45-17 is 1.6%, BUT the car comes stock with 16'' and 205/55/-16 and compared to those, difference is 0.4%. Negligible, either way.