Tare weight explained: tare, ATM and GTM for caravans

The four trailer weights

• Tare: the trailer empty, as it left the maker. Water, gas, batteries added later, and your belongings are extra.
• ATM: the maximum loaded weight of the trailer, measured as if standing on its own, so it includes the weight that will sit on the tow ball. This is the figure you compare with the vehicle's towing capacity.
• GTM: the maximum weight the trailer's axles may carry when it is hitched. Because part of the load is on the tow ball, GTM is lower than ATM.
• Tow ball weight: the part of the trailer's weight carried by the tow vehicle. It counts against the vehicle's GVM.

A worked example

A caravan with a 2,100 kg tare and a 2,600 kg ATM has 500 kg of payload. Water tanks, gas bottles, a second battery, an annexe, food, clothes and bikes on the drawbar can use all of it. Hitched with a 260 kg ball weight, about 2,340 kg sits on the van's axles, and 260 kg is added to the tow vehicle.

What tare includes, and what it does not

Transport for NSW gives a precise definition. Tare mass is the caravan with no load, unoccupied, with all standard equipment and any options fitted at the factory. Fluid reservoirs needed for transport are counted full, but water tanks and wastewater tanks are measured empty. After-market add-ons, which Transport for NSW lists as things like a TV, mattresses, extra gas bottles and awnings, are not in the tare. They are load, and they count against your ATM.

That is why a brochure tare can be optimistic. A van ordered with a dealer-fitted annexe, a second battery, an extra water tank and a roof air conditioner may leave the yard weighing well over its plated tare, and every one of those extras has come out of your payload before you pack a pillow.

Transport for NSW's packing example

Transport for NSW works through an example that shows how fast the margin goes. A caravan with a 2,100 kg tare and 2,500 kg maximum carrying capacity leaves 400 kg to pack. Then the extras:

The holiday pack in the same example, luggage, kitchen gear, a barbecue, groceries, bedding, two bicycles and outdoor furniture, adds another 191 kg. The total is 458 kg: 58 kg over. Nothing in either list is unusual. That is the point of the example, and why Transport for NSW says to weigh everything you load.

Where the weight sits matters too

ATM is a total, but the van also has to be loaded in the right places. Transport for NSW says heaviest items low and centred over the axles, lightest items high and spread out, to reduce snaking or sway. The NSW Government's towing guidance adds about 60 per cent of the load forward of the axle centre and a level or slightly nose-down drawbar. Our tow ball weight guide covers the share that ends up on the car.

Weights that grow on the road

The van you weigh at home is not the van you tow home. Grey water, a full toilet cassette, firewood, wine and souvenirs collected along the way all add kilograms. Transport for NSW specifically reminds caravanners to allow for the grey water tank, cassette waste and items picked up while travelling. If you leave home close to ATM, you may be over it by the end of the trip.

How to find your van's numbers

Every caravan built for Australian roads carries a vehicle plate, also called a compliance or VIN plate, usually on the drawbar or near the door. Depending on when it was built, it shows the ATM and often the tare and GTM. The manufacturer's handbook gives the same figures. If the plate is missing or unreadable, or the van has been heavily modified, a public weighbridge reading and an engineer's advice are the way to find out where you stand.

Common weight terms side by side

Weigh it

The only reliable figures are measured ones. Take the loaded rig to a public weighbridge and weigh the van alone, the vehicle alone, and both together; a tow ball scale gives the ball weight at home. Then check all four limits in the calculator.

Weighing at a public weighbridge, step by step

Transport for NSW points caravanners to the national list of public weighbridges and suggests confirming the weighbridge is calibrated. A simple sequence that gives every number you need:

1. Load everything as you travel: water tanks as you tow them, gas, food, bikes, people in the car.
2. Car and van together on the bridge. This is the combination mass to compare with the GCM, if your car has one.
3. Car alone, van still hitched, with the van's wheels off the bridge. This is the loaded car, including the ball weight: compare it with GVM.
4. Van alone, hitched, with the car off the bridge. This is the load on the van's wheels: compare it with GTM.
5. Van alone, unhitched, resting on its jockey wheel. This is the ATM figure to compare with the van's rated ATM and the car's towing capacity.

The difference between step 5 and step 4 is approximately the tow ball weight. Write each number down and keep the ticket; it is useful evidence if your insurer ever asks.

The lowest limit wins

Transport for NSW's example makes the rule concrete: a car rated to tow 3,000 kg, with a towbar and coupling rated to 3,500 kg, behind a van with a 2,500 kg ATM can only tow 2,500 kg. The van's ATM is the lowest figure, so it sets the limit. The loaded van must stay under every one of these: the towbar and coupling rating, the vehicle's towing capacity, the van's ATM, the GCM if one is given, and the tyres' rated capacity.

Tare and kerb weight are not the same idea

For a car or ute, the empty figure is usually called kerb weight or kerb mass, and it typically includes a full tank of fuel and fluids but no people or load. For a caravan, the equivalent is tare. People sometimes compare a car's kerb weight with a van's tare and think they are measured the same way; they are not, so always work from the definitions on the plates and in the handbooks.

Buying a new van: weight questions to ask

1. What is the tare of this exact van as built, with the options I have chosen, not the base model?
2. Can I have the weighbridge figure for the actual van before delivery?
3. Which options and dealer add-ons are not included in the tare?
4. How much payload is left between that tare and the ATM?
5. How full are the water tanks assumed to be in your figures?
6. What is the ball weight with the van empty, and where do the tanks sit relative to the axle?

A van with a 500 kg payload on paper and 350 kg in reality is a different purchase. Ask before you sign, not after the first weighbridge visit.

Upgrading a caravan's ATM

Just as some vehicles can have a GVM upgrade, some caravans can have their ATM re-rated, usually by the original manufacturer or with engineering approval, and usually with stronger axles, springs or tyres. It is not a paperwork exercise: the chassis, suspension, tyres and brakes all have to be rated for the higher figure. It also does not help if the tow vehicle is the limit. Before chasing a higher ATM, check the car's towing capacity, tow ball rating and GCM, because the lowest limit still wins.

Signs a van is overloaded

• The van sits noticeably nose-down or tail-down when hitched, despite adjusting the hitch height.
• Tyres look squashed at normal pressures, or run hot after a drive.
• The tow vehicle's rear squats and steering feels light.
• The rig sways in crosswinds or when trucks pass, more than it used to.
• Brakes feel weak or fade on long descents.

Any of these is a reason to visit a weighbridge before the next trip. Transport for NSW notes that overloading is both unsafe and illegal, and that non-compliance can affect your caravan insurance cover.

Water: the easiest weight to manage

Water is the heaviest thing most caravanners carry, at a kilogram a litre, and the easiest to adjust. Travelling with full tanks when you will pass towns with water every day adds 100 kg or more for no reason. Fill up close to where you will camp instead, and carry drinking water in the tow vehicle only if its payload allows. Check where each tank sits relative to the axle, because a full front tank adds to ball weight while a rear tank reduces it.

Tare weight for camper trailers and box trailers

The same definitions apply to every trailer, not just caravans. A camper trailer's tare includes its kitchen, tent and fitted options; a box trailer's tare is the empty trailer. For a box trailer, the ATM on the plate is what decides whether it needs brakes once loaded: a trailer with a 750 kg ATM that you load with soil or green waste can be over the limit without looking it. Weigh loaded trailers rather than guessing.

Why it matters for insurance

Transport for NSW warns that non-compliance is likely to affect your caravan insurance cover, and that overloading risks a fine. An insurer assessing a claim after a crash can ask what the rig weighed, and a van found to be over its ATM, or a tow vehicle over its GVM, gives them a reason to question the claim. A recent weighbridge ticket showing the rig under every limit is the simplest protection.

Tare, ATM and the tow vehicle's capacity

A common mistake is to compare a van's tare with the car's towing capacity. The comparison that matters is the van's loaded weight, which must never exceed its ATM, against the car's capacity. A van with a 2,300 kg tare and a 3,000 kg ATM can only be towed by a car rated to tow 3,000 kg if you load it fully; if you are sure you will never pack more than 300 kg, the loaded van weighs 2,600 kg, but the weighbridge, not the plan, is the proof. Many people choose a car with spare towing capacity so that ordinary trips are not right on a limit.

Common questions