top of page


As of 1st October 2017, 50mm Tow couplings will have to coincide with Section P of VSB6 revision 3, issued 1st July 2017. We have developed the following Table for you as a quick reference for allowed coupling ratings.

Don't get caught... You can't say we didn't tell you now!

Please refer to the chart below regarding the new rules on the 50mm 3.5 Tne ball and coupling. 

Looking at the attached chart, Column 1 is the GVM of your Truck, then go to Column 2, under the heading of 3500 kg, and the weights below is the ATM of the van or trailer allowed to be towed by your vehicle. 


ATM is the combined weight of the trailer and its full load when it is not coupled to a tow vehicle.  The ATM for your vehicle is found on the manufacturer’s plate on your van/trailer.

For example:

  • A 5000 kg GVM vehicle can only tow a maximum of 3445 kg ATM

  • A 16,000 kg GVM vehicle can only tow a maximum of 2338 kg ATM

  •        A 22,500 kg GVM vehicle can only tow a maximum of 2243 kg ATM

Solving some of the problems about towing caravans, whether it be behind a truck, car or 4 WD.

We are hearing about travellers being pulled over and weighed and finding out they are overweight on the van and also with their vehicle.

There are a few important considerations when it comes to towing regulation compliance:

1.  The GVM (Gross Vehicle Mass) of the vehicle doing the towing.

2. The ATM (Aggregate Trailer Mass) of the towed vehicle.


The ATM is the weight of towed vehicle loaded, ready to go.

3. The tare weight of both vehicles.

By knowing the tare weight, this will guide you as to how much weight you can put into the vehicles and not exceed the G.V.M and the A.T.M.

4. Know the Ball weight of the towed vehicle, empty and loaded.  


This is very important, as it will come into the calculations of the G.V.M of your towing vehicle.

5. The GCM (Gross Combination Mass).  


You must also be aware of your GCM while taking into account your GVM and ATM.  You must NOT exceed the GCM.  If your GCM is lower than the combination of GVM + ATM, you can only load your vehicles to the GCM rating.  To find out your GCM rating, you must contact your dealer or manufacturer.


This is Very Important.

We are hearing about vans / trailers that have been incorrectly marked on the manufacturer's plate.  This has happened to someone we know.

To overcome any issues we suggest you empty out your van / trailer, drop all water and remove any add-on's you are able to weigh i.e. Gas Bottles.  (Empty gas bottle vary a little in weight approximately 8.8 kg.)  You can deduct the amount of gas in the bottles off your weight when you tare weight your vehicle.

  • Most gas bottles are filled with 8.5kg of Gas

  • Water weighs in at approximately 1 kg p/ltr.

To find the ball weight of your van / trailer, you can weigh your hitch with devices available on the market.  Another way is to take both vehicles to a weighbridge and weigh both vehicles coupled up.

  1. On a single bridge weigh your towing vehicle and move forward and weigh your van / trailer.  

  2. With van / trailer still on the weighbridge, uncouple this vehicle from the towing vehicle and you'll find your van / trailer will be a heavier reading.

  3. Do this exercise both with van / trailer unloaded and loaded. 

    1. On a split weighbridge, you won't have to move forward as you will place one vehicle on one half of weighbridge and van / trailer on the other half of weighbridge.

  4. Once you have the weights of your vehicles, simply uncouple both vehicles and you'll see the difference in weights of both vehicles.  That will be your ball weight.

  5. Once you have your tare weights and unloaded ball weight we suggest you weigh all your goods you removed from your van / trailer as you place it back into the vehicle.

  6. Calculate your water volume (i.e. 100 litres of water will be 100 kg) and amount of gas in bottles.

  7. Once you have loaded your van / trailer and towing vehicle, re-weigh your vehicles and get your loaded ball weight of this towed vehicle.

  8. That ball weight will form part of your G.V.M of the towing vehicle.

Make sure your certified towbar has the equivalent or higher ball load rating.  It will be on the certification plate on your towbar.  You should have approximately 10% of your A.T.M on the ball or coupling.

Another important part of Towing van / trailers, is tyre pressures.  If your tyre pressure is too low it will cause too much bouncing from soft tyres and will also cause too much tyre rolling on the rims. This will be felt when cornering in and out of bends on the roadways.

Too much pressure will also cause a rough ride and bouncing. Play with tyre pressures until you are satisfied with the ride of your vehicles.

For smaller Tow vehicles, anti-sway bars or load sharing bars are essential as these will keep your vehicle from swaying.

We suggest if you find your weights are different on the plate on your van / trailer, contact the manufacturer and have a talk to them to see if the problem can be rectified.

For small vehicles towing vans/ trailers, if your weights are too great, you may not be able to tow your van / trailer with that vehicle.

For large vehicles and trucks, if your actual weights are greater than the manufacturer's plate, you will also have a problem when pulled up and weighed by the authorities.  Even though your vehicle is big enough to tow your van / trailer, the authorities will go by the manufacturers plate weights.

For trucks from 5000kg G.V.M. and over, have restrictions on the A.T.M. of van / trailer you can tow on the 3.5 Tonne 50mm Ball and coupling.  Check our information in the table above, and you can give us a call for further information.

Once again, it is very important to check all your weights before you can calculate whether you are legal or not.  


Do not take for granted that the plate on your van / trailer is correct at the time of delivery as customers request different after market equipment fitted after point of manufacture.

We hope this information can help you continue to be safe and legal on our roadways.

bottom of page