Differences in the metals and/0r the thickness of the wheels (I assume these are rims) means they can take higher or lower pressure and loads.
NOTE: these are the ratings for the metal.. Now when you apply rubber it too has ratings, both a max capacity and a max PSI (The standard mold says something like
Maximum load of 3,000 pounds at maximum pressure of 90 PSI
(Numbers picked out of air do not represent any actual tire)
This means if you are (in the fictional example) only loading the tire to 2500 pounds.. You use LESS air pressure.. The tire maker will tell you which.
But if you have tires which max out at say 120 PSI, and rims that max at 100 PSI,,,, Use the tire maker's pressure chart, but do not exceed the rim's ratings.