Do Not Trust Caravan Declared Mass

updated February 2019


As you may have read in our RV Weight Definitions article, Tare Mass is:

'the total mass of a trailer when not carrying any load but when 'ready for service'.

This is a shortened form of the full technical definition of Tare Mass which can be found in VSB 1 here and which states:

'Tare Mass is the total mass of the trailer when not carrying any load, but when ready for service, unoccupied (if relevant) and with all fluid reservoirs (if fitted) filled to nominal capacity except for fuel, which shall be 10 litres only, and with all standard equipment and any options fitted. This includes any mass imposed onto the drawing vehicle when the combination vehicle is resting on a horizontal supporting plane. (Fluid reservoirs do not include water tanks and waste water tanks fitted to caravans).'

Why You Cannot Trust Caravan Declared Tare Mass

Tare Mass is legally the weight of something (in this case a caravan) when empty. It matters with caravans because it determines the weight of everything you may legally load into it. (For the purposes of this article, the terms Weight and Mass can be seen as meaning the same.)

In practice, Tare Mass is the declared weight of a caravan as it leaves the factory. It is recorded on a 'Compliance' plate usually attached to the caravan's chassis by its manufacturer. With rare exception of caravans from a very few makers (e.g. Jayco) that weighs each individually, many manufacturers produce only totally basic unitsmodels. They leave it to the dealer to supply and install 'optional extras. This may apply even if you had included those options on your original order. 

The author has experiences this personally. The order (for an upmarket camper trailer) was placed directly with the manufacturer. Upon delivery that manufacturer insisted on supplying only via a dealer. That dealer supplied and fitted (very badly) my few optional extras. These were not included in the declared Tare Mass. The true Tare Mass was 80 kg higher (adding 10% to the weight). There far worse than this. 

False Tare Weight Matters

A caravan has two main legal weights: its Tare Mass, and its Aggregate Trailer Mass (the most it can legally weigh for use on-road). The weight difference is its maximum legal payload - and may be only 100-150 kg when the water tank is full. If the Tare Mass is (say) understated by 50 kg, that reduces payload to 50-100 kg. If understated by 100 kg (and that has been known) there is no legal payload.

Why you Cannot Trust a Caravan's Declared Tare Mass? - first tie up your camel!

Desert dwellers have a saying - 'trust in God - but first tie up your camel'. Both RV Books and the Caravan Council of Australia (CCA) recommend never to hand over your final payment until you have personally seen your caravan weighed on a registered weighbridge. The buyer-oriented CCA advises this be a clause in the original buying contract. RV Books totally endorses that. (The CCA's website includes a suggested buying contract. 

Aggregate Trailer Mass
The caravan maker must also set and disclose 'Aggregate Trailer Mass' (ATM). This is a legal rating. It is the maximum the laden caravan may weigh when standing (uncoupled to the tow vehicle) on a flat surface.


Payload is the weight of everything that exceeds its declared Tare Mass. This includes the water in the tanks, grey water (dirty water stored in a tank for later disposal), the gas in the gas bottle/s, solar modules and their regulators, extra batteries, awnings (if not added by the maker), books, food  plus all personal belongings.

Legally, the actual permitted payload is thus caravan's Aggregate Trailer Mass minus its actual Tare Mass. That declared Tare Mass may, or may not, be correct. The law, however, relates to what it the Tare Mass actually is. .

How much payload is provided?

There is no legal requirement about payload for Australian caravans, only a de-facto agreement by most caravan makers made decades ago. It is suggests about 250 kg for single-axle caravans under 1500 kg, and 250 to 350 kg for dual-axle caravans. There is no legal obligation for caravan manufacturers to provide such payloads. The actual payload many or may not be disclosed by the vendor, but it can readily be established by weighing on a certified weighbridge. It is its actual weight minus its actual Tare Mass. 

A few caravan makers tailor-make their products to provide the payload you require. This may no longer be feasible post 2019 as new regulations require caravan makers to submit a product that cannot then be changed by the maker. Be aware, however, that most locally-made caravans are already heavy - and increasing payload (and thus ATM) is likely to necessitate a heavier tow vehicle.

Is overweight a problem with Australian caravans?

Overwhelmingly, the evidence is YES. Ongoing police checks show that almost 80% (of those checked are overweight in one or more areas, some seriously so. One checked was over by 400 kg). See: https://rvbooks.rocketsparkau....on this website.  

Tare Mass - What's Included and What's Not?

The legal  term 'ready for service' included in the definition of Tare Mass, implies that Tare Mass must include everything required to operate the trailer. That is made totally clear by the included 'and with all standard equipment and any options fitted'.

BUT Tare Mass specifically excludes water, gas and all dealer-fitted options after the caravan has been finished at the factory and there weighed. Dealer-fitted options may be any number of appliances - including microwaves, air conditioners, solar panels, extra batteries, TVs or washing machines. Some of these are heavy.

All these items reduce your payload allowance - and few first-time buyers realise that the declared Tare Mass does not include water or LP gas.

 If you have 200 kg of water in two  x 100 litre tanks, two gas bottles and a dealer-fitted air conditioner and washing machine, you may be looking at 300 kg of extra weight that must be added  to the Tare Mass established at the factory. If your caravan has a legal payload of 350 kg, that would leave you with only 50 kg for all of everything else (fill two LP gas bottles and it's down to 33 kg!). If that allowed payload is 250 kg - that caravan cannot legally be used on a public road. Is is already 100 kg overweight. In the event of being in this situation the Caravan Council Australia can assist.

Tare Mass Variations

The actual Tare Mass of a trailer is legally required to be stamped on the trailer's compliance plate. Jayco apart, only a few caravan makers weigh every caravan they make, usually only samples of a particular model. The law, however, requires that Tare Mass be the mass of that caravan as it leaves the factory. The often-used vendor argument that 'there will inevitably be minor weight variations between individual caravans of the same model, due to associated variations in the quantities and quality of materials used' is true - but totally irrelevant.' Tare Mass is what it is - not what it should be.

The legal situation in such issues is that the legal vendor is the dealer. Do not allow a dealer to attempt to pass the responsibility to the caravan  maker.

How to Safeguard Your Payload

When you order a new caravan, ask the dealer to calculate its likely payload based on the exact options and accessories ordered and (if satisfactory, taking into account water, gas requirements etc.). Insist on this payload figure be included in the purchase contract as a condition of sale.

Prior to final payment, insist that the caravan is weighed when 'empty' at a weighbridge. Have this done in your presence (making sure that batteries, gas bottle, mattresses and drawers etc.have not been removed for weighing), and that the difference between this (its true Tare Mass) and the caravan's ATM equals the agreed payload.

There will be slight differences as temperature changes affect the load cells used in weighbridges  but the measurement is typically less than plus/minus 0.5% (5 kg per 1000 kg). Do not take delivery of the caravan if it is over declared its Tare Mass by more than that.

RV Books strongly recommends not to rely on the Tare Mass figure stamped on the caravan's compliance plate to calculate payload until you have had the caravan weighed on a public certified weighbridge. Those in Australia are listed at: 

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