What info does the label on the door have.
Mine has 60 lbs front and 80 lbs rear for max load. Chevy - not a ford but should need similar pressure.
My last truck had 80 lbs front and rear for max load.
Found this info on the net:
20" tires are size LT275/65R20. Here is the load inflation table for that size tire:
PSI . max weight single
--- . ------
35 . 2080
40 . 2280
45 . 2475
50 . 2680
55 . 2850
60 . 3030
65 . 3195
70 . 3375
75 . 3540
80 . 3750
"Single" means one tire on each end of the axle, not duals.
So with 65 PSI in the rear tires, you could have up to 3195 pounds on each rear tire, or 6390 pounds on the rear axle, without overloading the tires. On the front axle - probably won't have over 5,000 pounds on the axle or 2,500 pounds on each front tire, so you need only 50 PSI in those front tires. Better to over-inflate than under inflate.
My last CAT scale data (12,400 GVWR trailer)
Steer Axle - 4900 lbs
Drive Axle - 6060 lbs
Trailer Axle - 9220 lbs
Gross Weight - 20,180 lbs
