Here is the tire chart for light truck metric tires.
Sorry for the illegibility but I am suppling it just to deminstrate the range of tire pressure for a given tire. Any manufacture will supply this chart upon request.
The 225 75 16 D rated tire depending on load can be inflated from 35 psi with a 1445 lbs load to 65 psi with a 2205 lbs load. Depending on your weight per tire you would select a tire pressure.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles