with a crew cab, diesel, 1100# of ballast and an 821# plow... FULL SIDEWALL PRESSURE! My tires happen to be 285/75-16... 65psi. If I had 265 E's, I'd run the full 80. More air helps carry the load without the tires squatting, which helps you clear curbs, and helps your power steering live a longer, happier life.