With almost 350k on my Ram I've figured a few things out with tires. If you go to a bigger tire than the truck came with tire shops tend to still use the specs on the door for psi. I went through several sets of Toyo mudders 20-25k each with the center wore out and plenty of tread on the outside. Then I started chalking my tires. I drive a lot of miles and I want to get my $$ worth , tires are expensive. I chalk every set of new tires I run on a straight section of road until I get a nice flat foot print, since I have been doing this I get 70-85k out of my tires. My 98 wrangler with 35"s, I run those at 18psi at each corner and got 73k out of the KM 2's, and drove great. I have a fresh set of KO'2's on it now and run those at 18psi as well. Drives excellent. My 05' Ram w/ Cummins last 2 sets of Toyo AT II's 285/75r18E I ran those 52psi in the front and 46psi in the rear and got 83k on the first set and 77k on the second set. I wanted fresh tires for hunting season or I could have made it to spring. Something changed with the Toyo tires on the second set they didnt work nearly as good in the rain and snow. I'm running Nitto Ridge Grapplers now 35x12.5x18F, 54psi front and 42psi on the rear. Ride is fairly good, not as noisy as the Toyo mudders though.
I do adjust my air pressures as I increase my payload...
I don't understand why some of you are running more psi (70-80psi) in the rear running empty, I can only guess these are stock size tires? If I ran my Toyo at II's at 60-70psi with no payload in the rain, I was spinning tires on the freeway and had a very harsh ride. This also why I've went with another tire too though...
G
