Load Limits and the Associated Lingo

Trailer load limits

Knowing and understanding load limits is one of the most important aspects of owning a trailer. Failure to abide to these limits can lead to heavy fines or accidents. Before we go into the rules and regulations of load limits, here’s a quick guide to the terminology relating to load limits.


overloaded truck trailer

Tare weight - refers to the empty weight of the trailer.

GTM (Gross Trailer Mass) - the maximum allowable mass vertically placed on the trailer’s axle(s) while the trailer is hitched to the tow vehicle, including the trailer’s payload (the maximum weight that can be loaded onto the trailer).

ATM (Aggregate Trailer Mass) - the tare weight of your trailer plus its maximum payload when it is not couple to the tow vehicle. This is the maximum your trailer is allowed to weigh in transit. This is a rating set by the manufacturer/designer and cannot be exceeded.

Payload – the trailer’s carrying capacity. In other words, this is the difference between the tare weight and its ATM. Modifications and additions to the trailer can very quickly eat into its carrying capacity and result in an overloaded trailer, or the inability to legally carry the really important equipment.

Tow ball mass (TBM) - the amount of weight the fully laden trailer imposes (vertically) on the tow ball of the tow vehicle. This is not usually a critical issue with small trailers unless the tow vehicle has a low TBM, as is the case with many small cars.

The tare weight, ATM, GTM and TBM can all be found on the trailer’s vehicle identification number (VIN) plate.

The importance of sticking to the load limit, and other issues

Abiding to the load limit for your trailer is extremely important as it can affect performance, safety and insurance. Because of this, the most important thing is that you build the correct trailer for the type of hauling you need to do. Once you have the right trailer, you need to be aware of the implications of overloading, no matter how tempting it might seem. Overloading your trailer can lead to failing brakes, overheated transmissions and broken suspension – all of which are extremely dangerous and can cause nasty accidents on the open road.

trailer tyre blow out

Besides overloading the trailer, one of the biggest mistakes many people make is loading the trailer incorrectly. This can cause your trailer to be off balance, making it difficult to control. A rough guideline is to make sure about 60 per cent of the total weight is in front of the axle. Items should be tightly secured to stop them from shifting during transit.

Another thing to check when carrying large loads is your tyre pressure. If you fully load your trailer and then drive with tyres that are under-inflated, you put yourself at a higher risk of tyre blow-outs and rollovers. Ensure you check the pressure of the tyres on both your towing vehicle and your trailer before setting out on the road.

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