If you're going to get the Goodyear Polyglas GT's, I think E-60/15's would be the right ones. If you decide to just put regular tires like T/A Radials....235-60/15 is about the same size as an E 60/15. My 71 Challenger conv has 275-60/15's on the back, and 245-60/15's on the front.
