Know your tare from your GVM: your guide to vehicle weights
Hitting the road with your caravan, camper trailer, or other mobile home happily rolling along behind you is one of life’s great pleasures. The freedom these adventures offer is without compare, which is why it is important to know how to do it in a safe and stress-free way.
However, it can be very easy to become confused with the list of acronyms and terminology that surrounds vehicle weights. There is a lot of them! Luckily, we can help simplify the definitions and what they mean to your next adventure.
Some important definitions
First, let’s look at what these terms mean individually.
Vehicle weights
Tare weight: This is the weight of an empty vehicle with all of its fluids but with only 10 litres of fuel in the tank.
Kerb weight: This is the empty weight of a vehicle with a full tank of fuel and doesn’t include payload including passengers, luggage, and accessories such as bullbars and roof racks.
Gross vehicle mass (GVM): The total weight of the tow vehicle – the kerb weight plus payload including passengers, luggage, and accessories.
Gross combination mass (GCM): This is the maximum total weight allowed for both the vehicle and trailer and is the sum of the vehicle’s GVM and the trailer’s ATM.
Payload: This is the maximum load your vehicle can carry according to the manufacturer. If you deduct your vehicle’s kerb weight from its GVM, what’s left is how much you can load into it. This includes all passengers and their luggage.
Trailer weights
Tare Trailer Mass or Weight (TARE): This is the weight of an empty trailer. The term ‘trailer’ covers everything you can tow or ‘trail’ behind a vehicle, from a single-axle box trailer or camper trailer to motorcycle and jet-ski trailers right on up to heavy duty multi-axle boat trailers and caravans. If it’s a camper trailer or caravan, its Tare Mass unlike a motor vehicle does not include fluids like water tanks, LPG tanks, toilet systems. Also known as Dry Weight for obvious reasons.
Gross Trailer Mass (GTM) or Weight (GTW): This is the maximum axle load that your trailer is designed to carry as specified by its manufacturer. It is the combined weight of your trailer and its payload but does not including the Tow Bar Download (see separate heading). The GTM is usually displayed on the trailer or in the owner’s manual.
Aggregate trailer mass (ATM): This is the tare weight of the trailer plus its maximum payload when uncoupled from a vehicle. This is also referred to as gross trailer weight.
Gross trailer mass (GTM): This is the weight of the fully loaded trailer on its own axle, which will be less than the ATM as it excludes much of the trailer’s underpinnings. Not to be confused with gross trailer weight, which is another name for ATM.
Why is vehicle weight important?
The first reason to read that list of definitions a second time is because of safety. For example, if you’ve bought a new vehicle with a 3000kg towing capacity, it does not necessarily mean you can tow a 3-tonne caravan. You also need to know your towbar strength and the total weight of the tow vehicle. You definitely don’t want to try to tow more than your equipment is capable of!
The second reason is that if your vehicle does not meet the loaded mass limits, you could be in trouble with the law. Especially if you are travelling to Queensland, law enforcement is keenly on the lookout for overweight cars and recreational vehicles. You could be issued a fine if you are found to be exceeding your maximum weight, and that’s a sure-fire way to ruin a holiday.
The third reason is efficiency. Even when following all the rules, towing will decrease acceleration and braking performance, reduce vehicle control, and increase your fuel consumption. Therefore, you do not want to exacerbate these factors by overloading your vehicle.
The best way to avoid a fine and stay safe is to use a weighbridge. Weighbridges determine the mass of a vehicle and are designed for use by caravans, trailers, and passenger vehicles, as well as trucks. You can search the internet for ‘public weighbridge near me’ or visit this page. With a clear understanding of vehicle weights and solid towing skills, you can enjoy your next trip with confidence.