The best method for determining a vehicle's towing capacity is to look up the vehicle's technical specifications in the owner's manual. If the manual is not accessible, all vehicles have their technical specifications engraved on a metal plate located on the door jamb near the latch.
In cases where neither an owner's manual nor a door jamb specification plate are present, a vehicle's towing capacity is determined by approximating the combined weight of the vehicle's listed curb weight, the passengers and the cargo. Subtract this combined value from the vehicle's gross weight to determine the maximum amount of weight the vehicle can tow. If the vehicle is not designed for towing, the safest option is to tow no more than 70 percent of the vehicle's gross weight, recommends CarsDirect.com.
Contacting a dealership is another option for determining towing capacity when a vehicle's owner doesn't have access to any technical specifications. The parts and services departments of dealerships maintain technical specifications for all models and years for each make of vehicle the dealership sells. Once the vehicle's towing capacity is determined, another factor to consider is the weight capacity of the tow hitch. The weight of what is being towed should not exceed the towing vehicle's capacity, regardless of the weight capacity of the hitch.