The 20" rims do not have the center drop down section allowing the tire bead to drop into it when installing the tire, without that, the bead will not stretch over the rim bead lip.
You're now on the hunt for 22.5 x 6.5 to 7" rims so you can run 9.00 x 22.5 tires.
Firestone RH-5 rims have a 5 degree bead seat angle, hence the "5" in the part number.
Mike B
