Towing weights explained. What you need to know before you hitch up.
GVM, ATM, GCM, payload, tow ball mass. What they mean, why all your limits have to pass at once, and how knowing your numbers before you buy can save you thousands.
Why it matters
Getting this wrong costs you.
Towing weights tend to get treated as a technicality. But not understanding your numbers before you buy is one of the most common and most costly mistakes people make when building a rig.
Your vehicle's ability to tow confidently depends on more than just the legal limits. A setup that is within its numbers but poorly matched will show up in how the rig feels on a long day. That is a vehicle choice issue, not just a compliance one.
And when the numbers are actually exceeded, the consequences are direct. An overloaded rig handles differently when it matters most. Insurance can fail you. And the fixes that follow, whether that is a vehicle upgrade, a GVM upgrade, or going back to the drawing board, are expensive in a way that planning up front would have avoided.
Safety
Exceeding weight limits increases axle stress and braking distances. Consequences depend on which limit and by how much.
Insurance
An incident while overloaded can leave you uncovered, whether or not you were at fault.
Legality
Being over weight is a road rule breach. Fines, vehicle defects, and failed roadworthy inspections are real outcomes.
Performance
A well-matched, correctly loaded rig makes long days towing easier on the driver, the vehicle, and the fuel bill.
From the road · Tim and Lauren
When we first set out, we planned for two weeks off-grid and packed as much food and water as we could carry. As an experiment, we got weighed before leaving. Three kilograms over GCM, 30 kilograms over GVM. The fix was not a new vehicle. We dropped 30 kg of extra water we were carrying, about 12% of our total water at the time, moved a few things around, and cleared both limits with everything else fine.
Simulating your weights in OSCA before you load up would have told us the same thing without the trip to the weighbridge. The mistakes are cheaper when they happen on screen.
The definitions
The weights you need to know.
There are up to eight weight limits your rig has to sit within, all at the same time. Not every setup is subject to all of them. Some vehicles do not carry a GCM, some caravans do not list an axle group rating. But the ones that apply to your setup all have to pass together. One over and the whole combination is non-compliant.
The rule
All applicable limits must be met at the same time. Passing seven and failing one still means the rig is non-compliant. Check which limits apply to your specific vehicle and trailer combination.
Your vehicle
Vehicle
GVM
Gross Vehicle Mass
The maximum your tow vehicle can weigh when fully loaded. People, cargo, accessories, and the tow ball download from the caravan all count.
Vehicle
FGAWR
Front Gross Axle Weight Rating
Maximum weight the front axle is rated to carry. Loading the rear can unweight the front, but the front still has its own limit.
Vehicle
RGAWR
Rear Gross Axle Weight Rating
Maximum weight on the rear axle. Cargo in the tub and the tow ball download from the caravan both land here.
Your caravan
Trailer
ATM
Aggregate Trailer Mass
Maximum the fully loaded caravan can weigh standing alone. Everything you pack, water, gas, food, clothes, gear, counts. Stamped on the compliance plate.
Trailer
GTM
Gross Trailer Mass
The loaded caravan's weight on its own axles only. Does not include the tow ball download. A fixed rated limit on the compliance plate.
The combination
Combination
GCM
Gross Combination Mass
Maximum the vehicle and caravan can weigh together. Two setups that individually look fine can still push the combined figure over this limit.
Combination
TBM
Tow Ball Mass
Downward force the caravan puts on the tow bar, roughly 10% of the loaded van's weight. Counts inside your vehicle's GVM, not as extra capacity.
Combination
BTC
Braked Towing Capacity
The heaviest braked trailer the vehicle is rated to pull. Your loaded caravan's ATM cannot exceed this number.
On tow ball mass
Tow ball mass sits inside your vehicle's GVM. It is borrowed from your payload, not added on top of it. Load the caravan heavier and the ball weight on the vehicle climbs too. That connection is what most people miss.
Payload
Your payload is smaller than you think.
Payload is the gap between your vehicle's kerb weight and its GVM limit. It is the budget you have for everything: passengers, accessories, food, water, and the tow ball download from the caravan. The problem is it disappears fast, and a lot of it goes before you pack a single bag.
GVM limit-Kerb weight=Your payload
Kerb weight is the vehicle with a full tank of fuel, no passengers and no cargo. Everything after that draws from your payload. Here is what a typical dual-cab touring setup looks like once the real numbers stack up.
Real-world example · Dual cab ute, touring setup
GVM limit: 3,230 kg
Kerb weight (stock)- 2,267 kg
2 passengers- 160 kg
Bull bar, roof rack, drawers, canopy- 220 kg
HD tyres, fridge slide, fridge, aux battery- 80 kg
Tow ball mass (from caravan)- 300 kg
Payload remaining for food, water, recovery gear, tools~200 kg
That is roughly 200 kg left for everything else in the tub. Two hundred kilograms sounds like a lot until you account for water, recovery gear, tools, and food for a decent trip. And that setup is not unusual.
How different setups use their payload
There is no standard. The way your payload gets used depends on what you carry, how many people are in the vehicle, and how the rig is built out. Here are three common profiles.
The couple
Dual cab ute
Rooftop tinny, snorkel
Bull bar, roof rack, fridge
2 adults, canopy
Outboard, tow ball weight
~1,000 / 1,000 kg used
The family
Wagon, 2+2
2 adults, 2 kids, dog
Roof rack, roof pod
Bikes, esky, kitchen gear
~640 / 850 kg used
The tourer
Solo, kitted
Rooftop tent, fridge
Winch, HD tyres
Steel bull bar, roof rack
Awning, suspension upgrades
~750 / 950 kg used
The pattern
Accessories and tow ball weight eat most of the budget before you pack a thing. The payload number on the brochure and what you actually have left are rarely the same figure.
On the caravan side
Tare weight is a starting point, not a fact.
A caravan's tare weight is what it weighs as built, with empty water tanks, no gas bottles, and no personal effects. Your payload is ATM minus tare. The problem is that tare is often unreliable, for different reasons depending on whether the van is new or used.
ATM-Tare=Caravan payload
New van
The plate can lag the build.
Dealer-fitted options are often added after the tare was stamped. If the van has been customised from the base spec, confirm the real as-delivered weight before relying on that plate figure.
Second-hand van
Assume the tare is wrong.
A previous owner's modifications rarely make it onto the compliance plate. Solar, batteries, bigger wheels, dust systems. None of that shows up. Until it has been weighed as-is, treat the figure as a guess.
Van payload also fills up faster than most people expect. Water alone is roughly one kilogram per litre. A 200-litre tank is 200 kg before you have touched the pantry. Add full gas bottles, food, clothes, bedding, and camp gear and a realistic touring load of 350 to 400 kg is easy to reach.
What you carry
Rough weight
Fresh water (200L tank full)
~200 kg
Two 9 kg gas bottles, full
~26 kg
Fridge contents (full)
~35 kg
Pantry and dry goods
~25 kg
Clothes, bedding, linen
~40 kg
Camp chairs, mat, outside gear
~25 kg
Tools and spares
~20 kg
What draws from your vehicle payload
Common accessories and what they weigh.
Every modification to the tow vehicle draws from its payload. Add each one into OSCA so the maths happens before the purchase does.
Accessory
Typical fitted weight
Steel bull bar
40-80 kg
Alloy bull bar
25-45 kg
Roof rack (alloy)
10-18 kg
Awning
10-20 kg
Drawer system
40-70 kg
Fibreglass canopy
60-100 kg
Winch
15-30 kg
Dual battery system
20-35 kg
Fridge (50-60L)
18-25 kg
Suspension upgrade (springs and shocks)
15-35 kg
Upgrade to off-road / heavy duty tyres
~25 kg each
!
GVM upgrades do not raise GCM
If you need a GVM upgrade, you will often also need a GCM upgrade. They are separate certifications. One does not automatically fix the other.
!
Not every vehicle can be upgraded
GVM and GCM upgrades are not available for every make and model, and vary by state and territory. Do not assume an upgrade is a guaranteed option before buying a vehicle already close to its limits.
!
Trailers over 750 kg GTM must have brakes
Any braked trailer needs a brake controller in the tow vehicle. Over 2,000 kg GTM, brakes must be on all wheels and include a breakaway system.
!
Setups change. Your numbers should too.
A new accessory, different water capacity, or a new caravan changes your actual weights. Track it in OSCA as you go rather than relying on a number from two upgrades ago.
There is more to it
Where you put the weight matters as much as how much.
Getting all the numbers within limits is the legal requirement. Getting the distribution right is what makes the rig actually drive well. A correctly loaded combination sits level with roughly 10% of the loaded van's weight on the ball, and heavy gear positioned over or forward of the caravan's axles.
Loading distribution, weight distribution hitches, axle placement, and what happens when you get it wrong are covered in detail in the companion guide below.
Caravan Weight Distribution: How to Load Your Rig Correctly
Ball weight, axle placement, what too much or too little looks like on the road, and how distribution affects sway.
RoadFit is a 45-minute remote session with a vehicle weighing specialist. Your vehicle, your caravan, your numbers, walked through live. You leave knowing exactly where your margins are.
