Understanding Weights

Towing terms like GVM throw many people. So, what does GVM, GCM, ATM and TARE actually mean? The team at Camper Trailers and Hybrid Campers have been doing some research for our blog followers.

Let’s start with a few of the key terms and words you will need to understand when looking to tow an RV around Australia. It can sound like gobble-de-gook to most people, but learning the lingo will ensure your safety on the road. Getting these calculations wrong might even void your insurance.

  • Tare mass: this is the mass of your vehicle or caravan with nothing in it. For your tow vehicle, this is how much it weighs at the manufacturer specification and will include fuel and coolant. For your caravan, it also goes by manufacturer specification. In both cases, you do not include any payload. Look for a sticker on your van to see your TARE weight.
  • ATM: short for aggregate trailer mass, this is calculated by adding the tare mass of your caravan to your maximum payload. This rating is set by the manufacturer and it is against the law to exceed it. You can find this information on your trailer manufacturers plate.
  • GVM: gross vehicle mass is the limit of weight that your car can support, including your car, your passengers, and your tow ball mass. Again, this is a rating set by the manufacturer that you cannot exceed by law. Usually found on a sticker inside one of the doors.
  • GTM: gross trailer mass is the same as above for your caravan. It does not include the portion of the weight which will be supported by the tow bar or the jockey wheel.
  • Payload: This is any mass that you add to your vehicle or caravan. Think about passengers, luggage, bull bars or other features put on as aftermarket additions, and tow ball mass.
  • Maximum payload: unsurprisingly, this means the maximum weight that you can add into the vehicle or caravan on top of the tare mass. With your caravan, you don’t need to include passengers who will be using the caravan after you park up, but only what will be inside when you are on the road. It does include water and gas and anything you have put into the caravan for transport.
  • TBM: tow ball mass is the mass that is exerted on the tow ball once your caravan is ready to go. When you hitch up, the TBM is included in your two vehicles’ payload, which is why you need to calculate it carefully.
  • GCM: combine the maximum gross mass of your trailer and your vehicle and you will get your gross combined mass.
  • TBD: tow bar download is the amount of pressure that the tow bar can handle. Usually, it should be between 10 to 15% of your GTM. View this blog post on tow ball weight.


Getting the right insurance is key

Investing in caravan insurance can be a minefield to newbie RV owners out there. It is important to get the right comprehensive insurance based on your particular set of circumstances. For example, are you travelling on bitumen, or do you plan to drive on dirt roads? Do you intend to park your RV permanently on-site? Are you a fair-weather camper? Does your RV sit on your driveway in the winter? There is not a one-size fit’s all policy out there. Here are our biggest tips:

Know your GVM, GCM and other weights

Do your sums

To recap, here are the sums you are going to need to know:

  • ATM = caravan tare mass + caravan max payload
  • GVM = vehicle tare mass + maximum payload
  • ·Maximum payload = ATM – tare mass – tow ball mass
  • GTM = ATM – tow ball mass
  • GCM = GTM + GVM
  • TBD / GTM x 100 = % of GTM
Sample Calculation

Ranger PX Dual Cab

Weight guide


Tare = 2200 GVM = 3200kg Maximum Braked Towing Capacity = 3500kg GCM = 6000 From the above information we can calculate the following: Maximum Payload when car is not hooked up to a caravan = 3200 – 2200 = 1000kg Maximum Weight of the car when hooked up to a caravan weighing 3500kg = 6000 – 3500 = 2500kg Hence, payload when towing a caravan weighing 3500kg = 2500 – 2200 = 300kg This means the combined weight of the occupants, fuel, the ball weight, any other optional extras and equipment fitted should not exceed 300kg! Which is totally impossible. In the case of this car, a more practical maximum towing capacity would be 3000kg. This would give us a 500kg payload even if the ball weight of the caravan is 300kg.
Understanding Your GCM

If you still don’t understand the jargon, and you need some professional advice and assurance, book a free safety check day by the Caravan Qld organisation.

GVM, GCM, Tare, ATM Towing Calculator

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