What is the difference between GVM and GCM?

GVM is the maximum loaded mass of the vehicle specified by the manufacturer or approval authority. GCM is the maximum allowed combination mass of the vehicle and trailer together.

What is the difference between ATM and GTM?

ATM is the total loaded trailer mass including the mass imposed on the tow vehicle. GTM is the mass carried by the trailer wheels when the trailer is coupled to the tow vehicle.

Does tow ball weight count as vehicle payload?

Yes. Tow ball download pushes down on the vehicle, so it uses part of the vehicle payload and affects GVM, rear axle load and tyre load.

GVM, GCM, ATM and GTM Explained

The short version

Every vehicle and caravan has limits. The main job is to make sure the real loaded weight stays under every relevant limit at the same time. Passing one limit does not mean the whole setup is suitable.

Term	Plain-English meaning	Why it matters
GVM	Maximum loaded mass of the vehicle as specified by the manufacturer or approval authority.	Passengers, accessories, luggage, tow ball download and a slide-on camper all use GVM.
GCM	Maximum allowed combined mass of the loaded vehicle and trailer combination.	A tow vehicle can be under braked towing capacity but still over GCM.
ATM	Maximum loaded trailer mass, including the mass imposed on the tow vehicle through the coupling.	This is commonly compared with braked towing capacity and the caravan's own rating.
GTM	Maximum loaded trailer mass carried by the trailer wheels when coupled to the tow vehicle.	Useful for checking trailer axle/tyre loading and estimating GCM without double-counting ball download.
Payload	How much weight can be added before a limit is reached.	Real payload is reduced by accessories, passengers, water, tools and gear.
Tow ball download	The downward weight the caravan places on the tow ball.	It counts as vehicle load and can push the tow vehicle over GVM or rear axle limits.

Worked example: slide-on camper

Ute payload check

A ute has a 3350kg GVM and weighs 2400kg on a weighbridge before the camper is fitted. That leaves 950kg before GVM. If passengers, accessories and loaded camper weight add 1000kg, the ute is estimated at 3400kg. That is 50kg over GVM before axle limits are even checked.

Worked example: caravan towing

GCM and ball weight check

A tow vehicle has 3500kg braked towing capacity, but its GCM is 6000kg. If the loaded vehicle is 3000kg including tow ball download, and the caravan has 3200kg on its wheels while hitched, the combination is 6200kg. Even though the caravan ATM may be under the tow rating, the combination is over GCM.

Authoritative Australian sources

These definitions align with Australian government terminology for vehicle and trailer masses. They are still simplified for buyers, so always check the exact compliance plate, manufacturer specifications and weighbridge result for your own setup.

Australian Government RVS glossary for ATM and GTM definitions.
Vehicle Standards Bulletin 1 for low ATM trailer guidance.
NHVR manufacturer mass limits for GVM, GCM and component ratings.
WA Department of Transport GVM and GCM FAQs for practical towing definitions.

Use the calculators

If you are comparing a ByondRV slide-on camper, start with the slide-on camper weight calculator. If you are comparing a ByondRV caravan, use the caravan towing calculator.

This tool provides an estimate only. Final suitability depends on your exact vehicle variant, compliance plate, manufacturer specifications, towbar rating, axle limits, tyre ratings, accessories, real loaded weights and certified weighbridge results. ByondRV must confirm final suitability before purchase.