for 30 inch tires, i'd go with 3.73 or 4.10. these are the 235/75x15 or 30x9.50 size tires. they both will measure less than a full 30 inches in most brands. check your door tag or the axle tag to see which gears are in there now, as you might not have to re-gear at all. 4.56 would be overkill unless it is a trail rig. you should have plenty of power for the 3.73 gears and the 4.10 gears wouldn't cost you too much in lost gas mileage. imho.