A towing capacity is established by the tow vehicle manufacturer. The key weights are:
• Gross vehicle mass (GVM),
• Gross combination mass (GCM),
• Maximum tow ball mass (TBM),F
• Tare weight,
• Kerb weight (KW), and
• Towing capacity.
With these specifications, you can work out your maximum payload and how much you can tow.
To find these weights, occasionally, you’ll find a stamp inside the doorframe of your car with the tow ball weight and towing capacity.
Your owner’s manual will have most of the information you need. If you need to search online for your towing capacity, be careful you look at the correct variant of your tow vehicle.
When in doubt, or you have lost the owner manual, get the information directly from the tow vehicle manufacturer or dealership, or even check www.redbook.com.au
The kerb weight of your tow vehicle is how much it weighs when it is fully loaded with oil, fluids, and a full tank of fuel but otherwise empty.
This includes accessories fitted after your car was built, including a roof rack, an extra spare wheel, bull bar, or possibly your tow bar.
Your vehicle’s tare weight is its empty weight with all fluids filled and 10 litres of fuel.
Like the kerb weight, the car is otherwise empty, and aftermarket accessories are not included.
Your maximum tow ball weight, also called tow ball download, is the maximum weight your tow vehicle is allowed on its tow ball.
When you connect your caravan to your tow vehicle, weight is transferred from the caravan to your car.This is because caravans are designed to be front heavy to keep them hitched onto your vehicle.
Your GCM mass refers to the maximum weight of the caravan and car combined, which is decided by the vehicle manufacturer.
Gross combination mass includes absolutely everything loaded into your caravan or car, such as people, accessories, luggage, food, fuel etc.
Your caravans tow ball mass is the downward weight of the coupling where it attaches to the tow vehicle. This is sometimes called ball weight or tow ball download.
There should be an empty tow ball weight on the compliance plate. If not, find your aggregate trailer mass (ATM) and subtract the gross trailer mass (GTM), which will give you your empty ball weight.
Keep in mind your tow ball weight will shift depending on if your caravan is loaded with more weight in front of or behind the axle, how full your gas bottles are, and if your water tanks are full or empty. It is a good idea to check with a tow ball scale before you leave on your trip.
Your caravan’s aggregate trailer mass (ATM) is the maximum allowable weight of the caravan and everything inside or fitted to it when separate from your tow vehicle. Included in the ATM is the weight of the caravan, water in the tanks, gas in the gas bottles, food, clothes, modifications, etc.
The ATM is set by caravan manufacturers when the caravan is built.
The maximum allowable weight on the caravan’s axles when connected to a tow vehicle makes up your gross trailer mass (GTM).
Since the ball weight of the caravan is being carried by the car, this is different to your aggregate trailer mass (ATM).
If you need to work this out, subtract the empty tow ball weight of the caravan from the ATM.
Your caravans payload is how much you can load into it. To work this out, simply subtract your caravans tare weight from its aggregate trailer mass (ATM).
Any weight added to your caravan after the build comes out of your payload, including modifications, gas in the bottles, water in the tanks, caravan accessories, etc.
Understanding these critical weights and what they mean will allow you to safely and legally tow a caravan. Create a list of these weights and take them with you when looking at caravans. Ensure you have the correct information for your vehicle’s specific make, model and variant.Below is a sample list of what the weights of your tow vehicle could look like:
• Gross vehicle mass: 3,350kg
• Kerb weight: 2,635kg
• Maximum payload: 715kg
• Maximum towing capacity: 3,500kg
• Maximum ball weight: 350kg
• Gross combination mass: 6,730kg
In this case, 3,500kg is the maximum towing capacity for this vehicle. This informs what caravans you can tow (and buy at a dealership without changing your Tow vehicle)
In this example, that leaves 3,230kg out of the gross combined mass (GCM). Subtract your vehicle’s kerb weight (KW), leaving 595kg to load your car.
If the caravan you’re towing has a ball weight of 350kg, that will leave 365kg from your car’s gross vehicle mass (GVM) or maximum
payload. Anybody in your vehicle, luggage, modifications etc., also comes out of your maximum payload.