Actually, it was the type of tire construction over 50 years ago, that required such relatively low cold(not yet driven) tire pressures in cars - ‘bias-bly’(criss-cross) construction. Running the cold pressures specified for modern radial-ply(perpendiculary to the rim) tires in those bias plies could result in a very rough ride with severely reduced contact patch.
Conversely, inflating modern radials to the pressures specified back in 1957, or 1964, could result in the TPMS warning light coming on in your instrument panel. And the shoulders of the radial ply tread could wear out in a matter of weeks, let alone months or years.
Radial tires, as a rule of thumbs, usually require an average of 5psi more cold pressure than their bias-bly ancestors. So a 1964 Buick specifying 26psi on bias ply might require 31psi cold in replacement radial tires.
Sorry for resurrecting an older thread, but I was browsing threads regarding tire pressure, and came across this conversation.