do you have any lift right now? or body lift, or just 31's on a stock suspension? if so and your planning on running 31s for a while i say just throw a lil bodylift on it and be done, if u plan to do alot of wheeling in the future and get a bigger set of tires down the road, go ahead with the 4" susp lift. the 31's will probaly look a little small on there but not that bad. and theres always room for bigger tires