I'd like to hear more about this too Kingsalami.
I actually just swapped a set of 245/40/18 Bridgestone Potenza RE970AS Pole Position for 235/40/18 because my installer showed me I didn't have much more than about 10-12 mm of space before the tire would be rubbing on the inside of the frame.
I was warned that if the tire flexed enough inside it would begin to wear into the inside of the tire.
I am wondering CAN you even fit 245/40/18's without rubbing inside.
@Qwaktastic can you shed some light on this? I think you said you are running 245/40/18 - is that correct?