let me speak up for those of us with not so large a tire.When I first put the 30"x15 tires on my stock heighth M38,I pulled the front left tire up on a brick @ 35 pounds and aired down from there.When the tread formed around the top of the brick and the sidewall bulged some,I stoped there.Wound up being 15 pounds with a stock 7 inch wide rim.This definately helped me grip somewhat with what I had.Now this is gonna sound stupid to ya'll but stock military NDTs and Willys drivetrain was actually designed NOT to get as much traction as what was capable with those machines.Slipage was the break-away point in saving parts.
So in running those 30 inch and later 31 inch MTRs,I had breakage problems.Kept up with the "big boys" but I paid for it in down time.
Now I have backed up and bought a set of old school bias ply mud grips that are 31x7.5x16.That is right on stock size.These things are 10 ply thick and I can air down to 5 pounds before the sidewall bulges noticebly.I won't run it like that for fear of turn the tires on my rims and ripping the tube inside the tire.I'm still running the 15 to 18 pound range.
Testing those tires out in december at UNF even on Danial and Kodak I couldn't tell much difference on traction compared to the MTRs.Now I just need to re-adjust my nerves for being really narrow .Stock rims have alot of backspacing compared to 8 inch wagonwheels with 10.5 wide tires on em.