First I'm no tire expert, but most of what you ask is general.
Over all diameter does not need to be that precise. If it does need to be precise, find the factory size for you truck. The original tire was bias ply, and radials are just not the same. The BFG 820 sound like a large tire IIRC.
There are two factors (and probably more), the side wall height, and the number of plys. The shorter the side wall height the harsher the ride and the more plys, stiffer the side wall. You don't need a lot of plys, if you don't haul heavy loads and the roads you drive are with out pot holes.
When I buy tires I usually buy tread width to match rim width. I want my sidewalls to be vertical. Radials are the best tire for mpg.
Larry
Last edited by LGriffin; 10/04/2008 11:56 PM.
