Towing for work as well as recreational purposes in Australia is a growing activity, and before you even consider hitching up a trailer, caravan, or other towable, you need to know not only the weight of what you’ll be towing but also the towing capacity of your vehicle.

The towing capacity is the amount of weight your vehicle can pull. It differs from payload capacity, which is the weight a vehicle can carry.

The Importance of Understanding your Vehicle’s Towing Capacity

Both in terms of safety and the law, you need to tow within the towing capacity of your vehicle.

What does towing capacity mean? This is the maximum weight your vehicle is able to safely tow, and it is based on recommendations from your vehicle’s manufacturer. You manufacturer will usually provide these figures in your vehicle’s manual as well as vehicle specification sheets, which are available on the website of the manufacturer. These will cite two separate figures:

  • Unbraked Towing Capacity: this is the towing capacity of a vehicle when the trailer does not have its own braking system.
  • Braked Towing Capacity: this is the vehicle’s towing capacity when the trailer/van/other being towed has its own braking system. This is usually connected to the braking system of the tow vehicle via the trailer cable.

The braked towing capacity is almost always significantly higher than the unbraked towing capacity.

You will also need to understand that towing capacity is also impacted by the load on the tow vehicle itself – including cargo, passengers, aftermarket modifications and additions, etc, and these will reduce your capacity.

How to Check the Towing Capacity of your Vehicle

You need to consider:

  • Kerb Weight (KW) – the weight of the vehicle, driver, oil, and full fuel tank.
  • Ball Load or Tow Ball Mass (TBM) – weight trailer/caravan exerts onto the vehicle when hitched to the tow ball and not supported by the jockey wheel.
  • Payload – total weight your vehicle can legally and safely carry – including passengers, luggage, ball load, added vehicle accessories.
  • Gross Vehicle Mass (GVM) – maximum weight of the tow vehicle including passengers, cargo, and tow ball mass.

GVM = Payload + KW

  • Tare Mass – empty/unladen trailer mass – the weight of the trailer /van with fitted accessories, empty gas tanks, empty water tanks – i.e. its weight as it is driven from the dealer for the first time.
  • Aggregate Trailer Mass (ATM) – combined weight of trailer/van and its full load. This is measured when the trailer/van is not coupled to the tow vehicle but is fully loaded. This is equated with your towing capacity.
  • Gross Trailer Mass (GTM) = ATM – TBM when the trailer/van is hitched.

The combination of your vehicle and trailer when fully loaded must weigh within the recommended Gross Combined Mass limit (GCM). It is illegal for your vehicle-trailer combination to exceed this weight.

GCM = GVM + GTM

First and foremost, read your vehicle manual or check your manufacturer’s website to determine this. If you are still unsure, contact your dealer or vehicle manufacturer directly to glean this important information.

Your local weighbridge will enable you to get an accurate measurement of the combined weight of your vehicle and trailer. This is important to determine so that you know you’re travelling and driving within legal limits for your vehicle.

Calculation Example:

How to work out gross trailer mass

 

The Vehicle

  • Kerb Weight (KW) = 2000kg

2,250 kg

  • Payload = 500kg

600 kg*

  • Gross Vehicle Mass (GVM) = 3500kg

3,200 kg

  • Towing Capacity (Aggregate Trailer Mass=ATM) = 4000kg

3500 kg

  • Tow Ball Mass (TBM) = 500kg

350 kg

 Your vehicle has a KW of 2000kg and the GVM is 3500kg.

Your Payload is 3500kg-2000kg so you have of 1500kg to play with.

The TBM affects your payload, so the actual total cargo and passengers you can carry reduces to 1500kg – 500kg = 1000kg.

 The Trailer 

  • Aggregate Trailer Mass (ATM) = 3750kg

3500 kg

  • Gross Combination Mass (GCM) = 3500kg + 3500kg = 7000kg
  • Gross Trailer Mass (GTM) = GCM – GVM = 3500kg

These are the highest allowable numbers for this example.

Ideally, your towing capacity is 80% of the maximum of what the caravan manufacturer states you can legally tow.

So you will work with a towing capacity of 3500kg x 80% = 2800kg.

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