I have 35's and have no desire to go bigger. But I know of 3 guys in our club that have 37's on their TJ's. They like to do hard trails where they scrape over rocks all day. I'm happy to do moderate trails and have no desire to push mine to the limits. I drive my rig to trail rides across several states at times. These guys with the 37's only drive around in town. Any ride it has to be trailered. They were smart enough to get rid of the rubicon lockers and go with ARB or E-lockers. Two are 4.0 with the 3 speed auto and are geared 4.56. One had some carnage with the rear axle this year, the other snapped a front U-joint recently. The other is a 4 cylinder with 5 speed manual, 5.13 gearing, which does pretty well since it doesn't seem to have enough power to break things.