he woulda been ok the tire calc is a wash between either on the front compared to the 17s he was running... only major difference from his previous set up with the 245/40/18 is the circumference is 3" greater than prev setup vs the 255/35 which is 1" more circ... not sure how that impacts tho because diameter is a wash between all 3 ... nice ride Adam !
18 wheels are a game of millimeters. Nothing is a sure bet. These cars all have different tolerances.
I've been running 18 inch wheels for a long time, had many different tires on the front and back.
Don't rely so much on a tire calculator, it could lead to costly mistakes. Tire companies sizes also vary, what is 10 inches with a nitto, may be 10.5 in a bfg and 9.5 with a sumitomo.
What kind of rubbing a person can tolerate is also different. Some people just don't care, some it drives insane. Other factors apply, do you put people in your backseat? Do you drive hard around corners? Are you willing to remove the quad shocks?
Guess my point is, you can't simply give advice based on a tire size calculator. It's good for a place to start, but doesn't necessarily carry over 100% to the real world, especially when it comes to width.
Honestly, if i were him, even after downsizing, i'd still be worried.