Understanding caravan weights and terminology is seriously confusing, especially if you’re new to the RV scene. ATM, tare, payload, GCM, GVM – what the heck does it all mean? Well, we’re going to explain it to you.
But first, here’s why it’s important to understand the terminology behind caravan weights:
- Your insurance company is unlikely to cover you if they find out your caravan or camper is overweight. You need to understand the terminology so that you can ensure your caravan is not overloaded.
- Much like the human body, being overweight puts strain on your chassis and running gear.
- Being overweight dramatically increases the potential for ‘death wobbles’.
- It’s the rules and you will be fined if your caravan is found to be overweight.
Now that you know why it’s important, let’s move on to what all those confusing terms mean.
Caravan weights and terminology – what does it all mean?
Tare
Also called: tare mass, tare weight, empty weight or dry weight
Tare is the weight of the caravan completely empty as it’s delivered from the factory. This means the water tanks are empty, the gas cylinders are empty and there are no people, luggage or aftermarket accessories in the caravan.
Caravan manufacturers provide information on tare weights so you can find it in the manufacturer’s handbook and on the vehicle plate.
TBW (Tow Ball Weight)
Also called: tow ball mass, TBM, tow ball load, maximum tow ball weight, maximum ball loading
TBW (tow ball weight) is the maximum amount of weight that is allowed on the tow ball of the towing vehicle. The manufacturer specifies this weight. Just to be confusing, your towing vehicle will have its own tow ball weight which you also must not exceed and you must use the lesser of the two limits. So if your caravan tow ball mass is 180kg and your towing vehicle’s tow ball weight is 300kg, you must work with the 180kg.
ATM (Aggregate Trailer Mass)
The caravan manufacturer sets the ATM and it refers to the maximum weight your caravan can reach when fully loaded and unhitched from your towing vehicle. Anything over this weight is deemed unsafe.
ATM weights includes the TARE weight plus anything else that has been loaded into the caravan. This includes water in the tanks, gas, aftermarket accessories and anything you usually travel with such as food and luggage. It’s up to you to make sure that whatever you load into your caravan does not exceed this weight.
Payload
Payload is important as it’s basically the amount of stuff you can add to your caravan. The payload is worked out by subtracting the tare from the ATM. This figure can quickly get eaten up by filling your water tanks, gas and esky, leaving you not much play room for other items.
Examples of payload items include:
- Non-standard accesories (for e.g. awning)
- Gas and water
- Luggage
- Food
- Bikes and kayaks
- Bedding
- Spare battery
- Toolboxes
Remember, caravan payload = ATM – Tare
GTM (Gross Trailer Mass)
GTM weights are also set by the manufacturer and it’s the maximum weight that your fully loaded caravan is allowed to be while hitched to the tow vehicle. The GTM is lower than the ATM. Why? Because some weight is distributed through the tow ball and it refers to the weight transmitted to the ground by only the caravan tyres. Find the GTM of your caravan on your vehicle plate or in the manufacturer’s handbook.
Thus GTM = ATM – TBW
GVM (Gross Vehicle Mass)
Also called: MLVM or Maximum Loaded Vehicle Mass.
Moving away from the caravan to vehicle weights, GVM is the maximum weight your towing vehicle is allowed to be and this is set by the vehicle manufacturer. It is a measurement of your fully-loaded towing vehicle with the caravan hitched. You’re not supposed to go over the GVM and unfortunately, this figure includes passengers. So if you have a seven-seater with every seat taken by a fully grown adult, this can be problematic in terms of weight.
GCM (Gross Combination Mass)
This is set by your towing vehicle’s manufacturer but not all vehicles are provided with a GCM. It’s the maximum amount that the combined mass of your loaded tow vehicle and loaded caravan hitched together can weigh. If your vehicle does have a GCM, you can usually find it in the vehicle manufacturer’s guide.
Towing Capacity
Also called: Maximum brakes towing limit
The towing capacity is the maximum weight that your vehicle can legally tow if the caravan has its own braking system. Older or micro caravans sometimes don’t have their own brakes so you’ll need to find out the Maximum Unbraked Towing Limit of your car.
So now that you understand the terminology, you can make sense of your caravan weights and ensure that you’re keeping them under the limits. If you do find that you’re over, make sure to read our earlier article on how to reduce your payload by 200kg. You’ll be surprised at how easy it is to drop some caravan weight!
