That created some controversy in the past, but just as experiment I keep old tire on my tag axle.
The tire is so old, that nobody knows how to read the old codes anymore, but it is estimated at least 30 years old (coach is 43 YO).
This is commercial tire, same size used on semitruck and I actually cut other old tire to discover that sidewalls do have 3/4" of rubber with fabrics in it.
I don't use the coach often lately, but the tire hold 80 psi for about 3 years till I drove the coach this summer again and pumped it to 90 psi.