Looking for guidance on how big a rim and tire I can run on an 08 F150 Lariat wd with a 6in lift. Thanks in advance for the help.

 

Well, rim width and backspacing is as important to fitment as lift height and tire size. This is why you can run a 35x12.50 with only a leveling kit by using the stock wheels and the same tire would rub like crazy using a 10 inch wide wheel with 4.5 inches of backspacing. Rim diameter doesn't matter, it's the width and backspacing/offset. But generally, most people running a 6 inch lift will use a 35x12.50 on a 9 inch wide wheel with 4.5 or 5 inches of backspacing.