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how much can trailers carry

How to Determine Your Box Trailer’s Carrying Capacity

Buying a box trailer is a cost-effective option for increasing your carrying capacity, allowing you to move supplies and heavy equipment with ease. However, you have to follow towing regulations. Otherwise, you put yourself at greater risk of an accident, and there’s a good chance non-compliance will invalidate any warranty or insurance.

If you’ve yet to use a box trailer or if you’ve just bought one, you might be confused about how to determine your towing capacity. We’ll teach you how to stay compliant with regulations and prevent accidents due to improper towing here.

Important Terms

How much you can tow is determined by one of two things, your vehicle’s towing capacity or your box trailer’s carrying capacity, whichever is lesser. To find out how much you can carry, it helps to first know some important terms:

  • Aggregate Trailer Mass (ATM): The maximum weight of the trailer when it’s fully loaded
  • Tare Weight: The weight of a trailer or vehicle when it’s not carrying anything
  • Payload: Any mass added to your trailer or your tow vehicle
  • Gross Vehicle Mass (GVM): Your vehicle’s tare mass plus its max payload, which includes the trailer ball load when it’s connected to a trailer
  • Gross Combination Mass (GCM): The maximum allowed weight of your vehicle and trailer combined

Determining How Much You Can Carry

All trailers built after August 1989 are required to have a plate listing their ATM and tare weight. You may not find its max payload on the plate, but it’s simply its ATM minus its tare weight. This is the maximum amount you can load onto your box trailer.

Your vehicle’s GVM and GCM are determined by its manufacturer. To determine its towing capacity, you take its GCM, subtract its GVM (note that its GVM includes any added mass, including passengers and accessories), and whatever’s left is how much your trailer is allowed to weigh, in other words, your towing capacity.

Neither the trailer’s ATM nor your vehicle’s maximum towing capacity should be exceeded. For example, if your vehicle’s towing capacity is 3,500kg and you’re towing a 3,500kg trailer with an ATM of 2,000kg, you trailer is overloaded. If you’re towing a 3,500kg trailer with an ATM of 3,500kg, but your vehicle’s towing capacity is only 2,000kg, your vehicle is overloaded.

Other Weight Considerations

Besides your carrying capacity, there are two more things you need to pay attention to. These are:

  • Gross Trailer Mass (GTM): The weight a fully loaded trailer puts on its axle when it’s attached to a tow vehicle
  • Tow Ball Mass: The weight a fully loaded trailer puts on your vehicle’s tow ball

Your box trailer’s GTM doesn’t have too much to do with its carrying capacity. Be aware that any trailer with a GTM greater than 750kg is legally required to be equipped with electric brakes. If you have one such trailer, make sure the brakes are working properly. The GTM can also be found on the trailer’s plate.

Your box trailer’s tow ball mass is important for its stability. If it’s too light, the trailer might sway while you’re driving. If it’s too heavy, the front of your vehicle gets lifted up, causing a reduction in steering response and a tendency to understeer. Your tow ball mass should be between 6% to 15% of your trailer’s total mass.

Safe Loading

Keep in mind that just because you’re able to load everything into your vehicle and trailer, it doesn’t mean you should. It’s also important to make sure everything’s secure and everyone’s comfortable.

Any load you’re carrying should stay put during normal driving conditions and even light collisions. Your vehicle’s cabin also shouldn’t be cramped. An uncomfortable ride will cause fatigue, and fatigued drivers are at greater risk of getting into accidents.

Safe and Durable Box Trailers

King Kong Trailers offers high-quality galvanised box trailers so you can safely transport cargo over long distances. Buy box trailers for sale in Sydney today.

Call us at 0415 999 399 or email us at if you have any questions. 

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