Assuming they are STOCK rims, as in the ones that came with the car,
205/75 will work and will be easier to find than the 195/75s usually
recommended.  The stock rims on a '54 should be 5" wide.  The reason
that I say only on the rims that came on the car is because the later
cars used 4.5" wide wheels which are a little marginal for anything
wider than a 195, and are usually outside the tire manufacturer's
recommended rim width range for a 205 tire.

good luck,

nate

Hello Evan,

I strongly suggest that you NOT put radial tires on stock Studebaker rims.
They were not designed for the stresses radial tires will impose on them.
Wheel failure is a definite possibility.  This has been discussed in
Turnings Wheels.  We, too, have a '54 Commander Starliner and I bought a
set of wheels from Bob Helm who advertises in Turning Wheels for the
P195/75R15 Coker wide whitewall radials that we have.  We have no
clearance problems with them, and they are very close to the same diameter
as the olde bias ply tires so from a few feet away, they have the same
appearance.

Yes, there are other modern wheels that will fit your car.  Others within
this group can suggest proper alternatives.  Be safe; use modern wheels if
you want to run radials.

Kindest regards,

Alan Mende
Hummelstown, PA