You can I believe safely use 225/75R16 or 215/85R16 without a lift, provided that your springs and shocks are in good shape. 235/70R16 should also be okay. 235/85 or 245/75 will probably require some lift and/or trimming. 265/75 definitely requires a substantial lift and trimming and adjustment of bump stops. Anything taller than stock effectively gears you up and arguably the RRC is overgeared from stock. I have 215/85R16 tires on mine ('92 3.9-liter) and I find it significantly overgeared. I don't find it a problem except when descending steep grades off-road, where as I say it was already overgeared with stock diameter tires. I'd love to go to taller tires (probably 235/85) but feel that I'd have to either go to lower ratio diffs (4.10) or stop going down steep trails. Another factor to ponder when considering taller tires and/or lower gears is that the axle components are already marginal in strength. Upgrading the rear axle isn't too costly but the front can get very pricey.