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The Truth about GVM’s and GCM’s and Six Wheelers.


GVM  Gross Vehicle Mass is the recommended maximum total weight of vehicle and load, including any people in the vehicle. 

GCM Gross Combination Mass is the sum of the GVM and the weight of the maximum loaded trailer.

In the case of utility vehicles, both these figures are set by the vehicle manufacturer and have more to do with the warranty than the law of the land.  The Federal law in Australia clearly states that, in the absence of a manufacturer’s recommendation, the vehicle is allowed to tow 1.5 times its tare (empty) weight.

The important thing to consider with a vehicle converted to become a Six Wheeler is that along with that conversion is a new Compliance Plate.  Six Wheeler Conversions Pty Ltd (SWC) is a registered 2nd Manufacturer.  So the first manufacturers recommended GCM goes out the window.

And the vehicle now tares a fair bit heavier as well.  As a rough rule of thumb, the Six Wheeler normally tares between 2.6 and 3 tonne.  This allows a trailer weight of between 3900 and 4500kg.  As long as it is braked properly.

Add to this the new GVM that SWC puts on the new compliance plate, the GCM is usually between 8 and 9 tonne.  This is all a fair bit safer than the combination would have been with the vehicle on only 4 wheels and within the original GCM.  The new combination has an extra axle giving better weight distribution, and better road grip,  and far better braking ability.  So overall a far better combination.

Then it gets even better if the trailer is a gooseneck type.  Once the trailer hitch is forward of the rear axle, then the ball weight becomes part of the load.  And it stops being a dead weight at the end of a towbar.  So the steering and load distribution on the vehicle becomes far better.  Gone are the tendencies of the trailer to sway and overtake control of the towing vehicle.   And the extra brakes help too.

But legally it helps as well.  Because a tonne or so can be on the vehicle as load,( and the trailer is then considered to be 3.5 tonne), then the lighter Six Wheeler can still legally tow a 4.5 tonne gooseneck.  This is the biggest trailer allowed with electric brakes.  After that you have to have a truck in order to get legal brakes.

And so, from a legal aspect, a Six Wheeler is the only sensible way to tow a gooseneck trailer.  And it is also the only safe way to control these trailers with heavy loads. Because of the way we build our new Dingo EYE- -TIE tray bodys, and the way we mount them to the chassis,  a gooseneck hitch can easily be added into the new tray as we build it.