I would like to know to, I have 33" Kumhos and their rated at 80 psi. I know that 60 psi is a very hard ride. I just aired them to 35 today and I can tell a difference.

 

Do a chalk test. Are the E or D rated? The E rated is a stiffer tire and will do better with lower pressures. What you want is a flat contact patch between the tire and road. I would guess you could go down to 27-30 lbs or so, depending on the tires rating