I run my front tires at 40 psi. No foam - air only. I run my rear tires at 16 psi. Rears are filled with Rim Guard. Both front and rear are R-1's - six ply.
16 psi in the rears give me a full chevron contact patch on hard, flat ground.
40 psi in the front because I lift "heavy" with my grapple.