I flipped the front and rear wheels on the Dart yesterday to see how much room I have. With a +27mm offset wheel and a 255/40/18 on an 18x9" wheel, I have about 3/4" of room on each side. A 275/35/18 might seem easier than I think, even with the +35mm Enkei's I was thinking about getting.

First 3 pictures display the room between the tire and the leaf springs, inner wheel well, and outer fender in the rear. Pictures are upside down.

Last picture is how close the wheel is to the outer fender in the front with -10mm offset (from +32mm to +22mm offset).

All pictures are from the driver's side.