1The caravan's numbers
Four figures belong to the van itself. They live on its compliance plate, usually on the drawbar, and they never change no matter what car you hook it to.
Tare: the van with nothing in it
Tare is the weight of the caravan as it left the factory. Empty tanks, empty cupboards, no gas in the bottles. It is the starting point for everything else, and it is the number brochures love to quote because it is the smallest one available. You will never tow a van at Tare. The moment you fill the water tanks and pack the fridge, that number is history.
ATM: the number that can get you fined
ATM (Aggregate Trailer Mass) is the maximum your loaded van is allowed to weigh when it is not hitched to the car. The manufacturer sets it based on the chassis, axles and suspension. Roll over a weighbridge above your ATM and you are unroadworthy, regardless of how strong your tow vehicle is. This is also the figure you compare against your car's braked towing capacity when checking if a van is even on the menu.
Payload: the one nobody advertises
Payload is simply ATM minus Tare, and it is the most useful number in caravanning. It is your entire allowance for everything you add: water, gas, food, bedding, chairs, tools, the annexe, the second battery the dealer talked you into. Water is the killer because every litre weighs a kilogram. Fill two 95L tanks and you have spent 190kg before a single bag goes in.
200kg sounds fine until you remember water, gas and gear all come out of it. Pack carefully in a van like this.
See full specs â1,500kg of headroom means full tanks and proper touring gear without sweating the weighbridge.
See full specs âBall weight: the small number with big consequences
Ball weight (also called towball mass or TBM) is the downward force the van's coupling puts on your towbar. For most Australian vans it sits around 8 to 12 per cent of the total weight. Too little and the van sways at highway speed. Too much and you overload the car's rear axle and towbar.
Real example: the New Age Caravans Road Owl Expedition publishes a ball weight of 290kg against an ATM of 3,300kg, about 9%. Your towbar and your car each have their own ball weight limit, and the lowest number in the chain wins. A 3,500kg towbar with a 350kg ball limit does not help if the car itself is only rated for 300kg on the ball.
2The car's numbers
Three more figures belong to your tow vehicle. These live on the car's compliance plate and in the owner's manual, and they are where most buyers come unstuck.
Braked towing capacity
The headline number, and the one every ute ad shouts about. It is the heaviest braked trailer the manufacturer allows the car to tow. The van's ATM must not exceed it. But it is a ceiling, not a promise: the other limits below often bite first.
GVM: Gross Vehicle Mass
The maximum your car may weigh fully loaded: people, fuel, luggage, accessories, and the van's ball weight pressing down on the towbar. That last part surprises people. Hitch up a van with 250kg of ball weight and you have just spent 250kg of the car's own carrying capacity. Add a bullbar, a fridge and a family and many dual-cab utes are over GVM before the van moves an inch.
GCM: the trap that cuts your real capacity
GCM (Gross Combination Mass) is the maximum of car and van together, and it is the sneakiest limit of all. Many vehicles cannot be at full GVM and tow their full rated capacity at the same time, because the two added together exceed GCM. The practical result: a "3,500kg tow vehicle" that is loaded for a family trip might only have 2,800kg of legal towing left. You find this out by doing the subtraction, not by reading the ad.
- âĒ braked towing capacity
- âĒ GCM minus your loaded car's actual weight
- âĒ what your ball weight limit allows (~10x the ball limit for most vans)
Our tow calculator runs this exact arithmetic against a database of Australian vehicles, or you can start from your car with the Can I Tow It? flow and see every van that legally fits.
3The classic mistakes
Letting water and gear eat the payload
Every litre of water is a kilogram. The Zone RV Summit carries 400L of fresh water. Filling those tanks uses 400kg of its 1,150kg payload straight away, before gas bottles, food, tools or a single camp chair. Two 9kg gas bottles add about 35kg with the steel. A typical couple's touring load lands between 300kg and 500kg all up. If the van's payload is under 400kg, you need to pack like you mean it or travel with tanks half full.
Checking the towbar but not the car (or vice versa)
The towbar has its own rating plate, separate from the car's limits. An aftermarket bar rated to 3,500kg and 350kg ball does not raise a car rated lower, and a factory car rating does not help if someone fitted a lighter-duty bar. Check both plates. Lowest number wins, every time.
Believing the headline tow rating
The GCM subtraction in section 2 is the one that catches experienced buyers. Loaded car plus loaded van must stay under GCM, and for a lot of popular utes and wagons that means the real-world towing figure is hundreds of kilograms below the number on the brochure. Do the sum with your actual loaded car weight, ideally off a weighbridge.
Comparing Tare instead of ATM
Dealers sometimes quote Tare because it sounds towable. You will never tow the van at Tare. Compare your car's limits against ATM, the fully loaded worst case, and you can never be caught out by your own packing.
4Staying legal
The rules are enforced against the plates, not the brochure. Your van's compliance plate carries its ATM and ball weight; your car's plate carries GVM, GCM and tow ratings. Those numbers are the law for your specific vehicle, including any options or upgrades it was certified with, so always read the plate rather than a spec sheet for the model. Our compliance plate guide shows where to find it and how to read it.
Penalties for towing overweight vary by state, so we won't quote dollar figures here, but all states can fine you and ground the rig on the spot. The bigger risk is an insurer denying a claim after an accident because a rated limit was exceeded. The fix costs almost nothing: load the rig the way you actually travel and drive it over a public weighbridge once. Then you know, instead of hoping.
Quick answers
What does ATM mean on a caravan?
ATM stands for Aggregate Trailer Mass. It is the maximum the caravan is legally allowed to weigh when fully loaded and not hitched to a car. It is set by the manufacturer and stamped on the van's compliance plate. Your loaded van must never exceed it.
How do I work out a caravan's payload?
Payload is ATM minus Tare. Tare is the van's empty weight as it left the factory. The difference is everything you are allowed to add: water, gas, food, clothes, tools, bikes, the lot. Water alone eats payload fast because every litre weighs one kilogram.
Is ball weight included in the ATM?
Yes. ATM is the total mass of the unhitched van, which includes the weight that sits on the jockey wheel (and on your towball once hitched). The related figure GTM, Gross Trailer Mass, is the weight on the van's axles only when hitched, so ATM is roughly GTM plus ball weight.
My car is rated to tow 3,500kg. Can I tow any van with a lower ATM?
Not automatically. Braked towing capacity is only one limit. Your car's GCM (maximum combined weight of car and van), its GVM, its ball weight limit and even the towbar's own rating all apply at the same time. Plenty of 3,500kg-rated utes cannot legally tow 3,500kg once the car itself is loaded up. Check the compliance plate and do the sums, or use a tow calculator that does them for you.
What happens if I tow overweight in Australia?
You can be fined and defected, penalties vary by state, and police and transport inspectors do weigh rigs at checkpoints. The bigger financial risk is insurance: if you have an accident while over a rated limit, your insurer can deny the claim. A public weighbridge visit costs little and removes the guesswork.