[RalphG]

I seem to recall 24 psi recommended for the early fifties Fords on bias ply tire. I've run up to 30 psi in the steel belted radials I have on the original Mercury rims but its like running on solid steel wheels unless you are perfectly smooth pavement. I don't do any long extended mile runs so heating of the sidewalls is not an issue. For long runs at high speed I might want to go up over 30 psi and then check the temp of the sidewalls.
Edit: 53 manual advises 26 psi front and 22 rear on sedans.