A trailer is rated based on the maximum weight capacity of specific parts of the trailer and its overall capacity. These weight ratings are determined with tests performed by the manufacturer according to government guidelines. The parts of the trailer included in the manufacturer's weight ratings commonly include the axle, tongue weight and overall capacity. These figures are used to determine the maximum amount of weight the trailer can support and how it will handle while it is loaded.
The total weight of your tow vehicle, trailer and everything they are carrying is referred to as the gross combination weight rating. This rating is used to determine how much weight your vehicle can tow, whether you will require a special permit and the overall maximum weight capacity of your vehicle. The GCWR is a major determining factor in whether you need a commercial drivers license to operate a vehicle pulling a trailer. Trucks that do not normally require a CDL to operate may require this license when pulling a particularly heavy trailer.
The tongue of the trailer is the support that attaches it to the vehicle pulling it. Tongue weight measures the amount of weight that the trailer distributes to the hitch of the vehicle towing it. Trailers with a relatively high tongue weight will unbalance lighter vehicles, causing them to lose traction on their front tires, thus reducing steering and breaking capacity. Trailers with a low tongue weight will sway behind the tow vehicle, making it more difficult to control.
The gross axle weight rating applies to the trailer and the vehicle towing it. This rating measures the maximum amount of weight that a single axle is designed to support. Trailers that are carrying more weight than their axle is designed are more likely to suffer a sudden mechanical failure. Vehicles towing trailers that weigh more than their GAWR are also more likely to break down and generally handle poorly on the road.
Most manufacturers provide the unloaded weight of the trailer. This information is useful for estimating the overall weight of the trailer when it is loaded, and the type of tow vehicle best suited for pulling it. Heavy trailers require vehicles with larger towing capacities and a higher GAWR. Heavier tow vehicles are also more stable when pulling heavy trailers.
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