One thing to consider in how big a tire to put on the back door is also weight. I had a 34" Tire and wheel on the back of my FJ and it ended up messing up the hinges from weight. I know of half a dozen other guys locally that are having alignment issues from their doors because of non-stock tires that are not even that big. If you want to go real big check on the weight first or make sure the door will handle it. I had to get the tire of the door and put it on the tire carrier. Thats why we make it. Sorry dont mean to plug a product but weight on the back door is a real issue.