My tires and wheels have seen better days. Currently they are 225/70/14. Can I go 255/60/15 and what rim width and backspacing will fit my factory suspension? TY
What you have (tire size) is plenty for the handling ability of the OEM suspension. Larger (wider) will fit, but it would only change the 'look'; which may be your goal.
I've attached a pic of my '63 with 215/70/15r black walls on Cragar SS (direct drilled; not 'omni-fit') wheels. It has a 'look' of a car from the mid/late '60s owned by a 'kid' (me at the time). The thin (approx 1" wide) white wall tires, with the OEM wheel covers was very common among the 'Dads'. The 'thin' red line tires were mostly Pontiacs. Just history.
I have drum brakes all around. Disc brakes reduce fade from retained heat, typically produced from racing, pulling a trailer, or lots of very hilly driving. I do not drive my 63 like that. If you plan on disc brakes, you may want to plan all that out before buying wheels/tires. Moving the center of gravity outboard from the OEM position may produce unintended OEM suspension issues.
I purposely did not want more rear wheel traction (wider tires) because I have a '383' sb with a 4 speed. When I 'spin' the tires, I want the tires to 'spin'; not break parts.
Just trying to be helpful.