if you have 27" non wire-on rims, aka hookless rims, or beadless rims, your tire may pop off with inflation above 80 PSI...

hooked rims became the standard sometime in the late 70's? and it became common for tires to be inflated to above 80 PSI. before that only tublulars, where the inside of the braking surface does not play a role in holding the tire on, were commonly inflated above 80 PSI.