The correct type of tow hitch depends on the gross weight of the trailer and its tongue weight. For most trailers, the tongue weight is approximately 10 to 15 percent of the loaded trailer weight. The tongue puts a constant load on the ball portion of the trailer hitch, causing it to break if the hitch is not designed to handle the amount of weight being towed.
Class I tow hitches are rated to carry up to 2,000 pounds gross trailer weight and 250 pounds of tongue weight. Class II hitches can tow up to 3,500 pounds and handle tongue weights up to 350 pounds. Trailers weighing up to 6,000 pounds with a tongue weight of 600 pounds require a Class III tow hitch. Class IV tow hitches can handle up to 10,000 pounds gross trailer weight and 1,000 pounds of tongue weight. Class V hitches have the highest towing capacity at 25,000 pounds of gross trailer weight. Tongue weight is not a concern because trailers this size are typically fifth-wheels or gooseneck trailers.
Using a weight-distribution system allows the hitch to tow heavier trailers. Weight-distribution systems balance the trailer with spring-loaded bars. The bars must be adjusted each time the weight of the trailer or its contents changes.