I've been researching this a fair amount as well. All depends on wheel width and backspacing/offset.
So far, I seem to have learned that the ideal/practical width for all four corners would be 255/55r18, fitting well on both 7.5" and 8" wide wheels (OE 18s included), and not extending much off the fender line, if any at all.
I currently run 235/60r18 all four corners on 18x7.5 steelies. they ride great! I love the fit on the front, but seems somewhat narrow for the rear.
Once I get a new set of 18" wheels, I'll be swapping the rears with 255/55r18 (same overall diameter as front ones, as well as factory 245/45r20 tires) and will keep the fronts 235/60r18.
I've seen photos of rears with 255 wide tires and I like the tire width to the challenger's rear end width ratio lol