Dave,
Thanks for the 411. I will probably be running 255/70R16 rear, and 235/70R16 front. They will be 7 inches wide, front and rear.
Of course this will be going on a 1940 with a front suspension that will match an AD truck, so there still is room for error.
How much clearance do you have to the bed? Mathamatically I should have 3/4 to 1 inch depending on offset used. Is that enough to account for suspension travel, tire roll, and articulation?
