Overloading is one of the most dangerous and most common mistakes made by caravan owners in Australia. Here's a plain-English guide to every weight rating you need to understand before you tow.
Overloading is one of the most dangerous and most common mistakes made by caravan owners in Australia. According to the RVSafe Road Safety Project — funded by the Federal Government and supported by the Campervan & Motorhome Club of Australia — weight-related issues are a leading contributor to caravan accidents, rollovers, and fatalities on Australian roads. Here's a plain-English guide to every weight rating you need to understand before you tow.
Between 2014 and 2018, there were hundreds of crashes involving tow vehicles on NSW roads alone, resulting in fatalities and serious injuries. A significant proportion were caused or made worse by overloading or incorrect weight distribution — problems that could have been avoided with a basic understanding of your numbers.
The Seven Weight Ratings You Must Know
1. Tare Mass (Tare Weight)
This is the weight of your caravan as it leaves the factory — empty, with no water, no gas, no gear. It's the number advertised on spec sheets and typically displayed on a compliance plate.
Why it matters: Tare weight is your baseline, but it tells you very little about real-world safety. A caravan that weighs 1,400 kg tare can easily hit 2,000 kg once loaded.
2. Aggregate Trailer Mass (ATM)
ATM is the maximum legal weight your caravan can be when fully loaded, including everything you've packed, all your water tanks, gas bottles, food, clothes, bikes, and accessories. It's set by the manufacturer and stamped on your compliance plate.
Why it matters: This is the number you must not exceed. Ever. If your caravan is weighed and found to be above its ATM, you are breaking the law and your insurance may be void.
3. Gross Vehicle Mass (GVM)
GVM is the maximum legal weight of your tow vehicle — including the vehicle itself, all passengers, luggage, and the tow ball download from your caravan.
Why it matters: Many people focus on caravan weight and forget that every kilogram of download from the caravan goes into your vehicle's GVM. Add a family of five plus camping gear and you can exceed GVM without even realising it.
4. Gross Combined Mass (GCM)
GCM is the maximum combined weight of your tow vehicle (at its GVM) plus your loaded caravan (at its ATM). This is the total legal weight of everything moving together.
Why it matters: You can have a vehicle rated to tow 3,500 kg and a caravan rated at 3,200 kg — but if your GCM is 6,000 kg, you may still be over the limit once your vehicle's loaded weight is factored in.
5. Tow Ball Mass (TBM) / Tow Ball Download
This is the downward force your caravan puts on the tow ball of your vehicle. Typically it should be 8–12% of the loaded ATM of the caravan.
Why it matters: Too little tow ball mass creates an unstable, swaying combination. Too much exceeds your vehicle's rating and can damage the rear suspension, reduce steering control, and lift the front wheels. Both scenarios can be fatal at highway speed.
6. Maximum Tow Ball Mass (TBM Rating)
Your vehicle's manufacturer sets a maximum tow ball mass — this is the most downward force your tow hitch and vehicle structure can safely handle. Check your vehicle's owner's manual or compliance plate.
Why it matters: This is often the most overlooked number. You can be within your caravan's ATM and your vehicle's towing capacity, but if your tow ball download exceeds the vehicle's TBM rating, you're overloading the coupling.
7. Payload
Payload is the difference between your vehicle's GVM and its kerb weight (the vehicle as delivered by the manufacturer, with a full tank of fuel). It's how much you can legally add to the vehicle — passengers, luggage, accessories, and tow ball download.
Why it matters: Modern SUVs often have surprisingly low payloads once you account for accessories and passengers. A popular family SUV might have a kerb weight of 1,900 kg and a GVM of 2,400 kg — leaving just 500 kg for five adults, luggage, and tow ball download. It adds up fast.
The 85% Rule — A Widely Followed Safety Guideline
While not a legal requirement, the caravan industry widely recommends that your loaded caravan should not exceed 85% of your tow vehicle's kerb weight. This is because at ratios above 85%, sway becomes much harder to control.
Example: A vehicle with a kerb weight of 1,800 kg should ideally not tow a loaded caravan heavier than 1,530 kg.
This doesn't mean towing more than 85% is automatically unsafe — it depends heavily on vehicle design, sway control systems, weight distribution, and driving conditions. But it's a good rule of thumb, especially for less experienced towers.
How to Actually Know What Your Loaded Caravan Weighs
This is where most people fall short. It's not enough to estimate — the only way to know your actual loaded weight is to weigh it.
Options for getting weighed:
- Public weighbridges — available at many rural townships and truck stops. Search "public weighbridge near me" online. Usually $10–$20.
- RV weigh days — run by organisations like RVSafe, CMCA, and state caravanning associations across Australia. Often free or low cost.
- Mobile weighing services — companies like Safe Weight, Travel Safe Mobile Weighing, and DwnUnder Caravan Weighing will come to your driveway or campsite and weigh your rig on-site.
RVSafe recommends getting a corner weight measurement — individual weights on each wheel — not just a total weight. This reveals whether your load distribution is correct and whether any individual wheel or axle is overloaded.
Weight Distribution Inside the Caravan
How you load your caravan is just as important as how much you load. Incorrect weight distribution is a primary cause of caravan sway — one of the most dangerous handling problems you can encounter.
The key principles:
- Heavy items low and over the axle(s) — keep dense items like water tanks, batteries, and tinned food low and centred. Never put heavy items in overhead lockers or at the very front or rear.
- Maintain consistent tow ball download — aim for 8–12% of ATM on the tow ball. Too little and your van will want to sway. Too much and your vehicle becomes unstable.
- Balance side to side — asymmetric loading puts unequal stress on the axles and affects handling.
What Happens If You're Overloaded
The consequences of overloading go well beyond a fine:
- Structural failure — chassis cracking, tow ball failure, coupling failure
- Brake failure — overloaded brakes overheat faster and fade on long descents
- Tyre blowouts — every tyre has a load rating. Exceed it and blowout risk increases dramatically
- Insurance void — most caravan insurers include weight compliance in their policy conditions
- Criminal liability — if an overloaded vehicle causes an accident, you may face criminal negligence charges
The RVSafe Resource
The RVSafe project is a Federal Government-funded initiative that provides free educational materials specifically for Australian RV users. Their guides, videos, and quizzes cover weight, towing, driving techniques, and compliance in detail. If you're new to caravanning or haven't reviewed your setup in a while, it's an excellent starting point.
You can also browse caravans with their full weight specifications — including tare, ATM, and tow ball mass — on Camplify Xchange, where verified listings from dealers and private sellers include compliance data.
Quick Reference Checklist
Before every tow, confirm:
- Loaded caravan weight is within ATM (weigh it, don't guess)
- Tow ball download is 8–12% of loaded ATM
- Tow ball download is within vehicle's TBM rating
- Vehicle GVM not exceeded (passengers + gear + tow ball download)
- GCM not exceeded (total combined weight)
- Tyre pressures set for loaded weight (check door sticker or manual)
- Electric brakes functioning and controller set correctly
- Safety chains and coupling pin secured
Getting these numbers right before you leave the driveway is the single most important safety step any caravan owner can take.
Further reading: RVSafe Weight Education | Camplify Xchange — Caravans for Sale
Part of the Camplify Xchange editorial team, sharing expert RV advice for Australian adventurers.
