I have an 01 Supercrew Lariat. I am looking to upgrade rims and tires from the stock 265/70r17s that the truck came with. I found some 20" x 8.5" rims that I like, but I am hesitant on buying them until I find some tires that I want. I have been told that the suggested tire size is 275/45r20, but this is too much of a street look for me, I want beefier ATs on the truck. Does anyone know how big I can go without rubbing or making any modifications to the truck (ex. Torsion Bars)? What I am looking for is max allowable depth and width of the tire. For example I found some BFGs that are 34.6x11.2. Is that too big, or how big can I go? What is the formula for figuring this out so I dont have to ask again. Thanks

 

What is the backspacing on the wheels? If it's the standard 4.5 or 5 inches, you can easily fit a 305/55-20 (33x12.50). A 285/65-20 (35x12.50) may work but it would be a very tight fit.
Also, you are right, a 275/45-20 would look ridiculus unless you lowered your truck.

 

The backspacing is 5.25" and the offset is +15. The 285/65-20 you mentioned is kind of what I was looking for. It worries me that you said it would be a tight fit. I don't want anything that will rub or will cause problems when I need to take it off road (mountain construction sites). I've narrowed it down to 2-3 tire types (in order of desirability), BF Goodrich A/T KO, Nitto Terra Grappler, and maybe, maybe Cooper Zeon LTZ. Whats your opinion?

 

All of those are excellent tires. As for the fitment, it's an odd wheel size/BS/tire size combo so you will probably have to mount one to make sure.