Towing weights explained (Australia, USA & Canada, UK)
Clear, sourced definitions for every towing weight rating and term used on vehicle compliance plates, registration certificates, and owner's handbooks.
Australia (Caravans & Trailers)
- Tare Mass
- The empty, unladen weight of the vehicle or trailer as manufactured, with empty water tanks and no cargo or passengers [RACQ; 4X4 Australia].
- ATM (Aggregate Trailer Mass)
- The maximum legal laden weight of the trailer when uncoupled from the tow vehicle, specified on the trailer's compliance plate [RACQ; WA DoT].
- GTM (Gross Trailer Mass)
- The maximum weight transmitted to the ground by the trailer's axles when coupled to the towing vehicle, which equals the ATM minus the tow ball mass [RACQ; WA DoT].
- Payload (Trailer)
- The total allowable weight of all luggage, water, gas, food, and accessories carried in the trailer, calculated as ATM minus Tare [RACQ].
- Tow Ball Mass (TBM) / Ball Load
- The downward vertical force exerted by the trailer coupling onto the tow vehicle's towbar ball, typically recommended around 8–10 % of ATM [RACQ; WA DoT].
- GVM (Gross Vehicle Mass)
- The maximum allowable laden weight of the tow vehicle alone, including passengers, fuel, cargo, accessories, and the tow ball mass imposed by the trailer [RACQ; WA DoT].
- GCM (Gross Combination Mass)
- The maximum legal combined weight of the fully laden tow vehicle and trailer together as determined by the vehicle manufacturer [RACQ; WA DoT].
- Towing Capacity
- The maximum trailer mass the vehicle manufacturer allows the vehicle to tow, distinguished between braked capacity and unbraked capacity (maximum 750 kg) [RACQ; WA DoT].
- Towbar Rating
- The maximum trailer weight and tow ball download stated on the towbar's compliance label; the legal maximum towable weight is the lesser of the vehicle towing capacity and towbar rating [RACQ].
- Rear Axle Rating (RAR)
- The maximum load that can be safely supported by the rear axle assembly, including cargo behind the axle and the leverage of the tow ball load [WA DoT].
USA & Canada (Trucks, RVs & Trailers)
- GVWR (Gross Vehicle Weight Rating)
- The maximum allowable total weight of the vehicle or trailer when fully loaded with occupants, fluids, cargo, and tongue weight, found on the door-jamb safety certification label [FMVSS 110].
- GCWR (Gross Combined Weight Rating)
- The maximum total weight of the loaded truck combined with the loaded trailer and all cargo and passengers, specified by the vehicle manufacturer [GMC].
- GAWR (Gross Axle Weight Rating)
- The maximum weight rating for an individual axle (front GAWR or rear GAWR) as listed on the door certification placard [FMVSS 110].
- Payload Placard
- The yellow-and-white Tire and Loading Information label stating: "The combined weight of occupants and cargo should never exceed …", against which all passenger weight, cargo, accessories, and tongue weight count [FMVSS 110].
- Tongue Weight (TW)
- The downward force that the trailer tongue exerts onto the hitch ball, typically recommended around 10–15 % of trailer weight for conventional trailers and 15–30 % for fifth-wheel/gooseneck trailers [GMC].
- Hitch Class & Ratings
- The maximum gross trailer weight and maximum tongue weight specified on the receiver hitch label for weight-carrying and weight-distributing configurations [GMC].
- CAT Scale
- A certified public commercial platform scale divided into individual axle platform pads (steer, drive, trailer) used to obtain exact legal axle weights and derive true tongue weight [docs/02].
United Kingdom (Cars & Caravans)
- MAM (Maximum Authorised Mass) / Gross Vehicle Weight
- The maximum legal operating weight of the car or caravan including all passengers, cargo, fluids, and nose weight, found on the manufacturer's plate [nidirect].
- Kerbweight
- The standard unladen weight of the car with full standard fluids, 90 % fuel, and typically a nominal 75 kg driver allowance [The Caravan and Motorhome Club].
- MTPLM (Maximum Technically Permissible Laden Mass)
- The absolute maximum operating weight of the caravan when loaded with all belongings, water, gas bottles, and fitted equipment [The Caravan and Motorhome Club].
- Nose Weight
- The static downward load placed by the caravan's hitch onto the car's towball, which must not exceed either the car's handbook limit or the towbar's plated rating [The Caravan and Motorhome Club].
- Gross Train Weight (GTW)
- The total combined weight of the laden car and caravan together on the road, shown on line 2 of the car's vehicle identification plate [nidirect].
- Towing Limit
- The maximum gross trailer weight the vehicle is legally approved to pull, specified separately for trailers with brakes and unbraked trailers (maximum 750 kg) [nidirect].
- 85 % Guideline
- An established safety recommendation from the Caravan and Motorhome Club suggesting that the laden caravan should not exceed 85 % of the car's kerbweight for beginners, up to 90 % for experienced drivers, and never 100 % [The Caravan and Motorhome Club].