It says on tires what the manufacture recemends at a certain load but I just fill mine up till they look good and all the tread is in contact. I fill my tires to the recemended psi when towing heavy stuff. 40 psi should be good as long as the whole width of the tread is contacting. If you want you can either put a piece of paper down and drive over it or wet your tires and drive a few feet to see exact contact patch.
I did just that,called Cooper tire and told them what tire I had and what it was on . They were more than happy to tell me what to run the pressure at. On the tires I have it's 45psi front 47 psi rear.
Showed a friend of mine an old theory the other day on his Ferd. He'd been running what the door jamb said for air pressure since he bought the truck in 05. I splained to him he should be running what the tire says instead. When he did, his MPG's in creased almost 1.5mpg! I run what's on the tire's wall. My Bighorns say 50 and that's what I run. My stockers said 80 and thats what I ran in them. Try it out and see what the fuel economy does.:w: The ride will be a little rougher, but hell, they're trucks right?:lol3:
I was running 45 in the front on mine, and tried airing up to 50 and almost all my steering wander (typical frame flex at the box) went away. Cooper 315-75r16 D rated. I run a lot less pressure in the rears since the tires greatly overrate the load capacity and it makes for better traction. 'Course I think them Toyo's are E rated, so you might need less pressure, and you have a different frame.
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