It has 15" on rear at 7" wide and 14" on front but fronts are 8" wide or I can go back to the 13" with the original hubcaps, I have both. I would think it would be easier to drive with the 13" wheels and tires but might be easier on interstate with 15" on rear - I wonder how that would affect RPM's say at 60MPH?

The rims on the car have less to do with highway speeds than the tire profiles.

A larger tire will have an effect on how your speedometer reads.

Most tire sites have a calculater that will give you the info you need.

Measure the diameter of the tires you have and do some math.

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Yeah....Im the one who destroyed this rare, vintage automobile.....

An 8 inch wide rim will need the right backspacing to fit on the front, and the tire will have to be super thin. About the widest rim I would recommend for a pre-67 A body would be a six inch rim.

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Casually looking for a Clifford hyperpak intake for cheap.