Loaded trailer mass
2,700kg + 280kg = 2,980kg
- 220kg below the trailer’s 3,200kg ATM rating.
- 520kg below the vehicle and towbar’s 3,500kg trailer limit.
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How to Calculate Your Towing Capacity
Posted in Motoring Tips
How to Calculate Your Towing Capacity, GVM and GCM
By Motorama | Updated: September 2026
Seeing 3,500kg braked towing capacity in a brochure can make towing look like a simple numbers exercise. In practice, that figure is only one ceiling.
Once you add a towbar, bull bar, canopy, drawers, passengers, luggage, fuel and the trailer’s towball download, the vehicle may reach its GVM, rear-axle limit or GCM before the trailer reaches the advertised towing figure.
That applies whether you are towing a caravan out of Brisbane, taking a boat towards Moreton Bay or pulling a loaded box trailer across Logan. The important question is not only, “What is this vehicle rated to tow?” It is, “What is the lowest remaining limit when this exact vehicle and trailer are loaded for the trip?”
Queensland requires the loaded vehicle, trailer, individual axles, tyres, coupling and complete combination to remain within their applicable limits. The driver is responsible for making sure the vehicle, trailer and connection are suitable and safely loaded.
The short answer: the lowest limit wins
Your usable towing capacity is the lowest limit created by:
- the vehicle’s maximum braked or unbraked towing rating
- the vehicle’s remaining GVM after passengers, accessories, cargo and towball download are included
- the vehicle’s remaining GCM
- the front and rear axle ratings
- the towbar and coupling ratings
- the trailer’s ATM and GTM ratings
- the maximum permitted towball download
- the load ratings of the vehicle and trailer tyres
A trailer can therefore be below the vehicle’s advertised towing capacity but still make the vehicle overweight.
Manufacturer towing calculators also warn that published weights are only a starting point. Exact vehicle weight varies with options, accessories and load, so the final combination should be weighed rather than calculated from brochure figures alone.
Towing weight terms explained
Towing capacity cannot be confirmed from one number alone. These ratings work together, and the lowest applicable limit determines how the vehicle and trailer can be loaded.
| Term | What it means | Why it matters |
|---|---|---|
| Kerb mass | The vehicle’s published base mass under the conditions stated by its manufacturer. The treatment of fuel, options and accessories can vary, so check the specification for the exact vehicle. | It is commonly used to calculate advertised payload, but it may not represent what the vehicle weighs after accessories have been fitted. |
| Payload | On paper, payload is generally the vehicle’s GVM minus its kerb mass. In real use, it includes people, luggage, accessories, cargo and towball download. | Every kilogram added to the vehicle reduces the remaining capacity before it reaches its GVM or an axle limit. |
| GVM Gross Vehicle Mass | The maximum permitted loaded mass of the tow vehicle. | The vehicle, passengers, fuel, cargo, accessories and towball download must remain below this figure. |
| GCM Gross Combination Mass | The maximum permitted mass of the loaded tow vehicle and loaded trailer together. | It may prevent the vehicle from using its maximum payload and maximum towing rating at the same time. |
| ATM Aggregate Trailer Mass | The trailer’s maximum permitted loaded mass, including the load it imposes on the tow vehicle through the coupling. | The trailer’s complete loaded mass must remain below its ATM rating. |
| GTM Gross Trailer Mass | The maximum mass transmitted to the ground through the trailer’s wheels and axles while the trailer is coupled to the tow vehicle. | GTM excludes the portion of the trailer’s load being supported through the towball. |
| Towball download | The downward load the trailer applies to the towball. It may also be called ball mass, ball weight or trailer nose weight. | It counts towards the tow vehicle’s loaded mass and can place a significant load on the rear axle. |
| Axle rating | The maximum mass permitted on an individual axle or axle group. | A vehicle can remain below its GVM while still exceeding its front- or rear-axle rating. |
| Braked towing capacity | The maximum loaded trailer mass the vehicle is rated to tow when the trailer has the required braking system. | It remains subject to GVM, GCM, axle, towbar, coupling, towball and trailer limits. |
The key point: maximum braked towing capacity is only one ceiling. Your usable capacity is controlled by the lowest applicable vehicle, trailer, axle, towbar, coupling, towball or tyre limit.
Queensland legislation defines ATM as the manufacturer-specified maximum loaded trailer mass, including the mass imposed on the tow vehicle. It defines GTM as the mass transmitted to the ground through the trailer’s axles when coupled.
Current manufacturer guidance also confirms that towball download uses vehicle payload.
How to calculate your actual towing limit
1. Gather the ratings for your exact vehicle and trailer
Do not rely on a generic figure for a model name such as “HiLux”, “Ranger” or “Triton”. Towing and mass limits can change with the:
- model year
- exact variant
- body style
- engine
- drivetrain
- transmission
- factory options
- tow pack
- approved GVM or other certified modifications
Find the vehicle’s GVM, GCM, braked and unbraked towing ratings, front and rear axle limits and maximum towball download. Check the owner’s manual, manufacturer specification, identification information and any applicable modification plate or certificate.
Then check the towbar placard, coupling rating and the trailer’s compliance plate.
Queensland’s current rules use the applicable manufacturer, RAV, compliance-plate or approved modification figures when determining mass limits.
2. Weigh the vehicle as it will be driven
The most useful starting number is not kerb mass. It is the vehicle’s actual loaded mass before the trailer is connected.
Load it as it will be used, including:
- the driver and passengers
- the normal amount of fuel
- luggage, tools and camping equipment
- fridge, batteries or drawer systems
- bull bar, towbar, canopy and roof racks
- recovery equipment
- child restraints
- anything carried in the tray, tub, boot or cabin
Use actual measured weights where possible. Accessory weights can vary considerably, so do not rely on a generic estimate for a canopy, bull bar, winch or long-range fuel tank.
Queensland’s definition of a vehicle load includes the driver, passengers, goods, fuel, water and readily removable equipment.
3. Add the towball download to the vehicle
When the trailer is connected, its towball download becomes part of the tow vehicle’s loaded mass.
Coupled vehicle mass = loaded vehicle mass before coupling + actual towball download
That result must remain below the vehicle’s GVM.
You must also check the front and rear axle loads. Towball download does not simply sit evenly across the vehicle. Its position behind the rear axle can increase the rear-axle load while reducing some load on the front axle.
4. Check the loaded trailer mass
The trailer’s actual loaded mass consists of the load supported by its axles plus the load transferred through the towball.
Loaded trailer mass = actual trailer axle mass + actual towball download
The loaded trailer mass must remain below the lowest applicable limit, including:
- vehicle braked or unbraked towing rating
- towbar trailer-mass rating
- coupling rating
- trailer ATM rating
The towball download must also remain below the lowest applicable ball-load limit stated for the vehicle, towbar, coupling or trailer.
5. Check the gross combination mass
Use one of these equivalent calculations:
Combination mass = loaded vehicle mass before coupling + loaded trailer mass
or:
Combination mass = coupled vehicle mass + actual trailer axle mass
Do not add the full loaded trailer mass to the vehicle’s already-coupled mass. That would count the towball download twice.
The result must remain below the vehicle’s GCM. Queensland law separately requires the loaded motor vehicle to remain below GVM, the loaded trailer to remain below ATM and the complete light combination to remain below GCM.
6. Check the axle, towbar, coupling and tyre limits
Passing the GVM and GCM calculations does not finish the job.
You must also confirm that:
- neither vehicle axle exceeds its rating
- the trailer axle or axle group remains within its rating
- the towbar is rated for the loaded trailer and towball download
- the coupling is suitably rated
- the tyres remain within their load ratings
- the trailer is correctly loaded and stable
- the required braking and safety equipment is fitted and operating
The towbar, coupling or axle limit may be lower than the headline vehicle towing capacity. Queensland guidance describes the connection as only being as strong as its weakest link.
Towing capacity worksheet
Enter the ratings for the exact vehicle, towbar and trailer, followed by the actual measured weights of the loaded combination.
Where more than one towball or trailer-mass limit applies, enter the lowest applicable figure.
| No. | Worksheet item | Your figure | What to enter |
|---|---|---|---|
| 1 | kg | Maximum permitted loaded mass of the tow vehicle. | |
| 2 | kg | Maximum permitted mass of the vehicle and trailer combined. | |
| 3 | kg | Vehicle rating for the exact model year, variant, body, drivetrain and transmission. | |
| 4 | kg | Maximum trailer mass shown on the towbar rating label. | |
| 5 | kg | ATM shown on the trailer compliance plate. | |
| 6 | kg | Enter the lowest applicable limit for the vehicle, towbar, coupling or trailer. | |
| 7 | kg | Actual vehicle mass with passengers, fuel, accessories, luggage and cargo before connecting the trailer. | |
| 8 | kg | Actual mass supported through the trailer’s wheels and axles while connected. | |
| 9 | kg | Actual measured downward load applied through the coupling. | |
| 10 | Loaded trailer mass Trailer axle mass + towball download | kg | The trailer’s complete actual loaded mass. |
| 11 | Coupled vehicle mass Loaded vehicle mass + towball download | kg | Vehicle mass after the trailer’s towball load is applied. |
| 12 | Combination mass Loaded vehicle mass + loaded trailer mass | kg | Total actual mass of the loaded vehicle and loaded trailer. |
Headline limit checks
These results only compare the figures entered. They do not assess individual axle, tyre or other compliance limits.
GVM check
Coupled vehicle mass compared with vehicle GVM
Enter the required figures
GCM check
Combination mass compared with vehicle GCM
Enter the required figures
Loaded trailer check
Compared with the lowest vehicle, towbar or trailer
limit
Enter all three trailer limits
Towball download check
Actual download compared with the lowest applicable
limit entered
Enter the required figures
This is not a complete towing-compliance result.
The worksheet does not assess front-axle load, rear-axle load, trailer axle limits, tyre ratings, braking requirements, coupling suitability or load distribution. A combination may remain below GVM and GCM while still exceeding another limit.
Worked towing capacity example
The figures below are hypothetical and are not tied to a particular vehicle. They are included to show how the calculation works.
Published ratings
| Vehicle GVM | 3,200kg |
|---|---|
| Vehicle GCM | 6,250kg |
| Maximum braked towing capacity | 3,500kg |
| Maximum towball download | 350kg |
| Towbar rating | 3,500kg / 350kg |
| Trailer ATM rating | 3,200kg |
Measured weights
| Loaded vehicle before coupling | 2,720kg |
|---|---|
| Trailer axle mass while coupled | 2,700kg |
| Actual towball download | 280kg |
Coupled vehicle mass
2,720kg + 280kg = 3,000kg
- 200kg below the vehicle’s 3,200kg GVM.
- This does not confirm that the front and rear axles remain within their separate limits.
Combination mass
2,720kg + 2,980kg = 5,700kg
- 550kg below the vehicle’s 6,250kg GCM.
- The towball download is counted only once in this calculation.
Towball download
350kg − 280kg = 70kg remaining
- The measured 280kg is below the entered 350kg limit.
- The rear-axle load and load distribution still need to be checked.
What this example shows
The combination remains below the headline GVM, GCM, towing, trailer and towball limits used in the example. That does not make it a complete compliance result because the front axle, rear axle, trailer axles, tyres, braking system, coupling and load distribution still require confirmation.
It also shows why the 3,500kg towing figure cannot be used on its own. Adding another 250kg of passengers or cargo to the vehicle would increase the coupled vehicle mass to 3,250kg, exceeding the 3,200kg GVM even though the overall combination would remain below GCM.
This also shows why the 3,500kg towing claim cannot be used on its own. Adding another 250kg of passengers or cargo to the vehicle would take the coupled vehicle mass to 3,250kg, exceeding the 3,200kg GVM even though the combination would still be below GCM.
How to weigh your towing setup
The safest way to confirm the calculation is to weigh the combination as it will actually travel. Keep the fuel, passengers, water, gas bottles, luggage and equipment consistent between measurements. Ask the weighbridge operator whether the site can provide:
- the loaded tow vehicle by itself
- the whole connected combination
- the trailer axle or axle-group mass while connected
- the front and rear tow-vehicle axle masses
- the individual trailer axle masses where required
These measurements allow you to calculate:
Loaded trailer mass = whole combination mass − vehicle-only mass
Towball download = loaded trailer mass − trailer axle mass
Coupled vehicle mass = whole combination mass − trailer axle mass
Repeat the check after material changes such as fitting a canopy, bull bar, drawers, batteries, roof racks or long-range tank, or adding bikes, water, tools or recovery equipment.
Queensland recommends using a public weighbridge when the loaded trailer or combined mass is uncertain. Ford’s current towing guidance likewise recommends weighing before and after accessories and loads are added rather than relying solely on approximate specification figures.
Queensland towing rules to remember
This article focuses on light vehicles and trailers. Requirements can change with the type, age and mass of the vehicle or trailer, so always check the current Queensland rules and the relevant manufacturer instructions.
Trailer brakes
Under the Queensland regulation currently in force:
- a trailer with a GTM of more than 750kg must have brakes operating on at least one wheel at each end of one or more axles
- a trailer with a GTM of more than 2,000kg must have a braking system the driver can operate from the normal driving position
- for a trailer over 2,000kg GTM, the brakes must activate automatically if the trailer breaks away, remain applied for at least 15 minutes and hold the trailer on a 12 per cent grade
The braking system required depends on the trailer's mass, design and applicable compliance requirements - not simply whether it weighs more than 750kg.
Towbar, coupling and safety equipment
The towbar must be suitably rated for the loaded trailer. Couplings, chains, shackles and attachments must also be suitable for the trailer and correctly connected.
A weight-distribution hitch can transfer load between the vehicle’s axles and help restore ride height and steering response. It does not increase the vehicle’s GVM, GCM, towing, axle or towbar ratings, and Queensland specifically warns against using one to compensate for a badly loaded trailer.
Registration, roadworthiness and passengers
The vehicle and trailer must be registered and roadworthy. People must not travel inside a trailer or caravan while it is being towed.
Insurance
An overloaded or non-compliant towing setup may affect insurance coverage, depending on the policy and circumstances. Check your policy wording and discuss your setup with your insurer where necessary.
Queensland Government guidance notes that a trailer may not be covered by comprehensive insurance if it is overloaded, unsafe, unroadworthy, non-compliant or above the vehicle’s towing capacity. Check the policy wording and discuss the setup with the insurer where necessary.
Frequently Asked Questions
Can I tow the advertised maximum with a fully loaded vehicle?
Does towball download count towards payload?
Is ATM the same as GTM?
Is towball download always 10 per cent?
Does a weight-distribution hitch increase towing capacity?
Find a vehicle that suits your towing needs
Choosing a tow vehicle starts with the trailer you intend to use, not only the biggest towing figure in a brochure.
Bring the trailer’s ATM, expected loaded mass, measured or expected towball download and your typical passenger, accessory and cargo requirements. The Motorama team can help you compare the published GVM, GCM, towing and payload figures of the exact vehicle variants you are considering.
The final loaded combination should still be weighed and checked against its owner’s manuals, plates and applicable Queensland requirements.
