Short answer: do not rely on brochure tare when ordering. Ask what the tare estimate represents, list every factory and dealer option, state the minimum usable payload you require, and record the agreed ATM and axle ratings in the order. Before final payment, match the completed VIN to its vehicle plate and RAV information and obtain suitable final-build weighing evidence. Advertised tare subtracted from ATM is not proof of the payload your completed caravan will deliver.
The three trailer masses in plain English
- Tare mass is the mass of the trailer ready for service but unladen, determined under the applicable definition. VSB 1 Revision 6 says standard equipment and fitted options are included, while caravan water and waste-water tanks are not filled for tare.
- Aggregate trailer mass (ATM) is the maximum total mass of the loaded trailer when not coupled, as specified by the manufacturer.
- Gross trailer mass (GTM) is the maximum mass transmitted through the trailer tyres when coupled and loaded as specified.
Payload is commonly described as ATM minus tare. That arithmetic is only useful when both figures apply to the exact completed caravan and when other limits—including axle group, tyres and tow vehicle—are respected.
Why the brochure may not describe your order
A brochure can be based on a base layout, prototype, earlier production run or estimated configuration. A family bunk layout may not weigh the same as a couples layout of similar length. Production methods, component suppliers and standard equipment can also change.
Options use payload unless the mass and ratings are adjusted appropriately. Common examples include:
- additional or larger batteries and solar panels
- air conditioners, heaters and inverters
- larger or additional water tanks
- toolboxes, stone guards, bike racks and rear storage
- upgraded suspension, wheels or tyres
- washing machines, larger fridges and extra appliances
- dealer-fitted awnings, cameras, antennas and accessories.
Ask whether quoted tare is a design estimate, an average, based on a prototype or measured for a completed caravan. If it is not VIN-specific, label it as an estimate in your comparison.
Work out the payload you need before shopping
Create a realistic loading list for the actual travellers and trips: water, gas, food, clothing, bedding, outdoor equipment, tools, hoses, leads, recovery gear, bikes and personal items. Add a margin for items people forget and for future accessories.
Do not use a generic per-person allowance as proof your payload is adequate. A remote couple carrying water and recovery equipment may need more capacity than a family using powered caravan parks. The requirement should come from your inventory and travel pattern.
What to put in the written order
| Order field | What to record |
|---|---|
| Exact caravan | Model, layout, dimensions, production specification and all inclusions. |
| Factory options | Every selected component and whether its mass is included in the quoted tare. |
| Dealer accessories | Who fits them, when, estimated mass and whether final weighing occurs after fitting. |
| Mass basis | Whether tare is estimated or measured and what tanks, gas and equipment state applies. |
| Ratings | Agreed ATM, GTM, axle-group, coupling, wheel and tyre ratings. |
| Minimum usable payload | Your agreed minimum after all ordered and dealer-fitted equipment. |
| Final evidence | Vehicle plate, RAV entry and weighing document for the completed VIN. |
| If it misses the specification | Written process and consequence before final payment or acceptance. |
The last row is important. Do not wait until delivery day to negotiate what happens if the completed caravan does not meet the agreed mass or payload specification. General contract or legal advice may be appropriate before signing.
Check ratings together, not one at a time
A higher ATM does not automatically create a usable or legal combination. Confirm axle-group capacity, tyre and wheel ratings, coupling rating and the chassis/manufacturer approval. The tow vehicle must also remain within its maximum braked towing capacity, tow-ball download limit, gross vehicle mass, axle ratings and gross combination mass.
Ball loading changes the mass carried by the tow vehicle and the trailer axles. Load location matters. A caravan can be below ATM and still overload an axle, tyre, wheel or the vehicle’s rear axle.
Before final payment: verify the completed VIN
- Match the VIN on the caravan, order, invoice, vehicle plate and RAV entry.
- Check the vehicle plate shows the promised ratings.
- Confirm every factory and dealer option is fitted before final weighing.
- Obtain the weighing document and the exact loading state: tanks, gas, loose items and accessories.
- Compare measured or declared tare with the agreed minimum payload.
- Check axle and coupling information, not only total mass.
- Record any discrepancy and use the written contract process before accepting or paying the balance.
Use a public weighbridge correctly
A public weighbridge can provide an independent measurement, but the method must match the question. A single total does not always reveal tow-ball download or individual axle loads. Ask the operator what measurements are available and record whether the caravan is coupled, what is loaded, water levels and who was in the vehicle.
After delivery, weigh the real touring combination with passengers, fuel, water and equipment. The live How to Weigh a Caravan at a Weighbridge guide explains a repeatable process.
When to use a specialist
Use an automotive engineer or competent mass specialist when a proposed rating change, unusual construction, axle configuration, modification or load-distribution issue needs assessment. An upgrade label is not enough; confirm the approval, component capacities and which limits actually change. Do not attempt structural or running-gear alterations based on online advice.
Before-order checklist
- Build your own realistic payload inventory.
- Ask what the quoted tare represents and whether it is VIN-specific.
- List all factory and dealer accessories with estimated mass.
- Record ATM, GTM, axle-group and component ratings.
- Write a minimum usable payload into the order.
- Specify final-build weighing and RAV/plate evidence.
- State what happens if the completed caravan misses the agreement.
- Check the complete tow-vehicle and caravan combination.
Take the next step
Read Caravan ATM, GTM, GVM and GCM Explained, calculate realistic loads with the Caravan Payload Calculator, and verify the combination in the Caravan Towing Calculator. Continue through the Buying a Caravan in Australia hub.