The overall diameter or size of the tire you can add to an ATV/UTV will be determined by the turning radius and the amount of room under the fenders. Typical tire sizes on utility ATVs or UTVs are in the 24- to 26-inch tall size, and this is on the 12-inch rim. Most machines can usually take a size, maybe two, bigger than the stock tire size without much trouble. Go any bigger and you will need to lift the suspension of the machine. Staying close to the stock tire size means you will not have any trouble with the stock steering geometry or driveline components.