I am just kind of curious in this area, but I have a FC S4 with 18x7" Enkei RS5's wrapped with 215/40 Parada Spec 2's. Since there are very few tire selections in this size and to get better braking and handling characteristics, I was curious to see how wide is safe to go on this size wheel. I am currently thinking about a 235 on the rear, or maybe a 245. Obviously, the height of the sidewall may make a difference, but is there a problem going this wide. i understand that the 215 is already about 1.5 inches wider than the rim, and a 235 or a 245 will be over 2 inches wider. I have heard of people going 2-3 inches wider before, but I am mainly concerned with making my handling worse.

Any input is greatly appreciated.