Australian 4WD and Adventure Show

Understanding Trailer and Vehicle Mass for Safe Towing

Ronny Dahl has been getting his new vehicle ready for towing. Ronny has done his fair share of towing in his time, but usually only a trailer or camper trailer. With his kids getting older, Ronny is getting into caravanning, and is learning there’s a difference between towing a caravan and a camper trailer – and a lot more to remember!

Learning the lingo


Most 4wdrivers have heard of GVM but might not be able to explain exactly what it means. GVM – Gross Vehicle Mass is calculated on your axle load ratings as explained below and means the maximum your vehicle can weigh when fully loaded as specified by the manufacturer. Your vehicle’s GVM figure will be shown of a weight placard which is found inside the vehicle, usually near the driver’s door. It will also be listed in the owner’s manual. The vehicle’s GVM is the weight of the vehicle including all accessories (bull bars, roof racks, winches etc) plus whatever is inside the vehicle – people, luggage etc. If you’re using the vehicle for towing, you will also need to account for the tow ball download in the GVM or payload – this is a percentage of the trailer or van’s weight forced down on the vehicle when hitched.

Kerb Weight or Mass

This is the weight specified by the manufacturer and includes a full tank of fuel, without occupants, luggage or cargo and with all standard equipment. Additional weight of optional features must be taken into account when calculating kerb weight. Note that this does not include any accessories such as bull bars, roof racks, canopies, additional driving lamps etc.


This is the maximum load your vehicle can carry in standard form and can be determined by taking the GVM and deducting the Kerb Mass. It is important to note this figure include all passengers, luggage and additional gear. Never exceed the maximum payload specified!

Axle Load Rating

Your Axle Load Rating is the heaviest load a given axle can carry on your vehicle, remembering that the front and rear axle may have different load ratings and when combined this makes up your GVM. It is important to remember that you can be under your GVM but over your axle rating it loaded incorrectly.


ATM (Aggregate Trailer Mass) is the is the maximum towing weight of the trailer or caravan as specified by the manufacturer. This total weight includes the weight of your trailer or caravan with anything that is inside it. The weight of a van or trailer will usually be displayed on the chassis plate and will also be in the owner’s manual. The ATM also includes the tow ball download, which is the proportion of the weight that is applied to the tow ball. For example: is the van or trailer has an ATM of 2500kg the down force on the tow ball is 250kg, and this needs to be included in the payload of the towing vehicle.


GCM – gross combined mass – is the maximum weight allowed for your vehicle and trailer combined, as specified by the tow vehicle’s manufacturer. The vehicle’s GVM and the trailer’s ATM will determine the GCM. It’s so important to know your GCM as this will determine whether it is safe for the vehicle to be towing the particular trailer. If you have determined the GCM and found that the vehicle should not be towing the trailer at the current weights, you would then risk voiding your insurance if you still choose to go ahead with the towing. Not to mention it is unsafe for you and other drivers.

How to weigh

The easiest way to measure these important weights is by using your nearest public weigh bridge which you can find by a google search (try https://goweigh.com.au). Public weigh bridges may be a traditional single deck with an operator on-site to assist you, or they might feature multiple decks and self-serve 24/7 kiosks with automated credit card payment. You you could also engage an independent weighing service to come to your home, this way you also know your axle loadings on both your tow vehicle and or your caravan or trailer. This is the most thorough way of weighing your vehicle as they use individual scales under the wheels.

Top Towing Tips!

Choose your caravan or camper trailer before you choose your vehicle. The last thing you want is to invest in a new 4WD only to find out it won’t be able to tow the caravan you have your heart set on.

Remember just because the manufacturer of the tow vehicle states it can tow a particular weight doesn’t mean it can with a full complement of passengers and load in the vehicle itself. The vehicles payload will be reduced by the downforce on the tow bar and not have the capacity within the GVM when attached to the trailer or van.

Make sure the tow bar you choose is designed specifically to suit your vehicle and your towing capacity requirements – tow bars are not something to skimp on!

Thanks to Phil Thornton from George Day Caravans and Motorhomes and Richard Nicholls from Adventure Offroad Training for these valuable towing tips. For more Tips and Tricks on 4WDriving, Caravanning, Camping, Fishing and Boating, visit 4wdshow.tv