10.00 X 20 are standard semi-truck tires. Look on the sidewall for a Load Range Rating. E, F, G, something like that…80 psi should be pretty close for your new prize…Once you know the load range, you can determine maximum pressure…
Load Range “D”, 8 ply rated, 65 psi max
"“E” 10 ply rated, 80 psi max
"F" 12 ply, 95 psi max