Glossary

Gross Combination Weight Rating (GCWR) or Maximum Train Weight (GTW) or Gross Combination Mass (GCM)—Theses ratings may be found in the Owner's Manual or in the tow vehicle brochure for the model year you own, usually provided by the dealership. The these ratings are the maximum allowable weight of the tow vehicle and the trailer combined. These ratings assumes that the tow vehicle and trailer have functioning brakes, with exceptions, in some cases, for very light trailers (normally less than 1,500 pounds). The rating information for USA vehicles may be found at FifthWheelSt.com under the Tow Rating menu tab. Additionally, you may learn more about these ratings by reading our article, A Lesson on Gross Combination Weight Rating.

Important Note—When any calculation is based solely on these ratings, regardless of any calculator or what a salesperson may calculate, one still needs to be careful not to overload the rear axle. In most situations like this, the towing capacity is actually limited by the published maximum towing capacity which supersedes any calculation results. Some manufacturers derate towing capacity (usually for conventional towing). Example: The GAWR may be exceeded when calculating this vehicle information: GCWR: 22,800, GVWR: 10,000, GVW: 6026, rear GAWR: 6,000. The published max tow of 16,300 supersedes GCWR calculation of 16,774. (i.e. GCWR-GVW=Tow Capacity)

Gross Vehicle Weight Rating (GVWR) or Maximum Authorized Mass (MAM) or Gross Vehicle Mass (GVM)—These ratings are printed on the certification label, usually located near the driver's side door. These ratings are the maximum allowable weight of the fully loaded vehicle, including liquids, passengers, cargo, and kingpin or tongue weight of any towed trailer.

Certification label indicating GVWR
Vehicle Certification Label Indicating GVWR

The GVWR, as required by National Highway Traffic Safety Administration (NHTSA), primarily considers the weakest link in the load bearing components such as the frame, axles, springs, brakes, rims and tires. Based on the lowest component rating within the load bearing components, manufactures assign the GVWR. NHTSA's safety requirement for GVWR is that the vehicle is expected to stop within a required distance when it is fully loaded to the max GVWR. This is appears to be a primary safety concern of NHTSA when tow vehicles are overloaded by too much pin or tongue weight coming from the trailer. Some owner's manuals may state: "The towing vehicle's brake system is rated for operation at the GVWR—NOT GCWR. Separate functional brake systems should be used for safe control of towed vehicles and for trailers weighing more than 1,500 lbs. when loaded." Exceeding the GVWR can result in premature mechanical failure and failure to stop within a safe distance resulting in serious injury or death.

Additional resource: 49 CFR 571 - FEDERAL MOTOR VEHICLE SAFETY STANDARDS (Title 49 Transportation, Part 571)

Gross Vehicle Weight (GVW)—The GVW is the combined weight of the vehicle and all passengers and cargo pieces in gross, that is to say, in total. The best weighing practice is to weigh your vehicle when it is fully loaded and appropriate fluid tanks are full and all expected passengers are aboard just as if you were ready to tow to the trip destination. When a new vehicle purchase is involved, it may necessary to use the manufacturer's published vehicle curb weight.

Curb Weight (Kerb Mass)—The curb weight of your vehicle is the weight of the automobile with all of the standard equipment and necessary operating consumables (e.g., motor oil and coolant), and a full tank of fuel, but without any passengers, cargo, or any other separately loaded items in it. Thus, the curb weight is the amount that the vehicle weighs when it's resting at the curb and not in use. This is generally the standard weight that the manufacturer assigns to the car. The manufacturer assigned curb weight of a vehicle may not be the same at the time of purchase due to dealer installed components or options. The curb weight information for your vehicle may be found in the Owner's Manual or at FifthWheelSt.com under the Tow Rating menu tab.

A Note About Curb WeightWhen the only option is to use the manufacturer's published curb weight, it is important to provide, as accurately as possible, the additional weight of the expected cargo and passengers, and, if desired, select the fifth wheel hitch option on the app when a hitch is not installed or the hitch weight is unknown.

Trailer Weight Rating (TWR)—TWR is the rated value for the maximum allowable weight of a loaded trailer for a specific tow-vehicle model and hitch type, as determined by the tow-vehicle manufacturer. A specific tow-vehicle may have multiple TWRs for weight carrying hitch, weight distributing hitch, fifth wheel hitch and/or gooseneck hitch. A tow-vehicle may also have a TWR for an unbraked trailer. (SAE J2807 definition)

TWR is also known as Maximum Loaded Trailer Weight or Max Trailer Weight Rating or Max Towing.

Some manufacturers will derate  the towing capacity below the available payload (GVWR) and GCWR calculations.  Additionally, the TWR may be a derated rating to prevent the rear gross axle weight rating  (Rr. GAWR) from being exceeded on select vehicles.

The published TWR will always supersede higher towing capacity results from GCWR and GVWR mathematical formulas.

Tongue Weight (TW)/Pin Weight (PW)—TW (for conventional trailers) and PW (for fifth wheel trailers) is the amount of vertical load applied to a hitch. Generally, TW should range between 10% to 15% of the conventional trailer's GVW and the PW of fifth wheel trailers should range between 15% to 25% of the trailer's GVW.

Tow-vehicle Trailering Weight (TVTW)—TVTW is base vehicle curb weight plus one 150 pound driver and one 150 pound front seat passenger, plus100 pound of optional equipment split evenly between front and rear axles, plus the tow-vehicle manufacturer’s available trailering package and/or any required trailering content and representative aftermarket trailering equipment. (SAE J2807 definition)

Tow Ready Vehicle/Truck—The fully loaded vehicle or truck with the driver and all passengers onboard, all desired cargo onboard, necessary trailering equipment installed, and necessary vehicle fluid tanks or reservoirs filled to normal or full capacity.

Realistic Vehicle Towing Capacity (RVTC)—This is a term we developed in association with using RV Tow Check. RVTC is obtained after the tow vehicle is configured tow-ready, and then calculation formulas for GCWR and GVWR are completed and compaired with the published TWR to learn the realistic vehicle towing capacity.

RVTC is also the initials for RV Tow Check.


Note: We have interpreted glossary terms from the UK and Australia the best we know how. If you are from one of these countries and find a mistake or can provide an improved interpretation or web link, please contact us.