How to weigh and measure your rig
We explain methods for an accurate read on the weight and balance of your rig.
Moving forward to the safer, more regulated 21st century, caravanning and its responsibilities are very different. The vans and vehicles weigh more, many of the vehicles are faster and more powerful and technology from the tyres up has improved out of sight.
The regulations, however, have also increased out of sight. As the driver, you are responsible for the appropriate vehicle and van loads. And while you may get away with it for a while, towing with illegal weights will catch up with you one way or another.
There is also the matter of rig balance; measured on a weighbridge, you can see if your balance across all axle groups is relatively even, which will help safety, ride comfort and reduce wear on the vehicle and van. You should aim to weigh each axle set to check that the rig is well balanced and no weight limits are exceeded.
FIND A BRIDGE
A web search will find your nearest public weighbridge. Most weighbridges are at commercial premises frequented by the sort of vehicles needing to measure payload. If you call the people at the weighbridge and ask when their quiet periods are, explaining that you want to weigh your caravan and vehicle, most operators should understand what you want to do.
If you have time, it is a good idea to visit the weighbridge twice. Take your rig unladen the first time, because this gives you a better baseline to more accurately calculate payload. Return the second time with the van loaded and ready to go on tour. Dealer-fitted accessories are usually not included on the manufacturer’s plate.
Make sure the gas cylinder(s), water tank(s) and fuel tank contain about the same amount of liquids as the next time you do a full payload weight check. Every litre of gas, water or fuel weighs approximately 1kg and may alter your readings.
STRIKING A BALANCE
Weighbridges vary in sophistication – many have one large pad, while others have a number of smaller ones. The advantage of multiple pads is you don’t need to move the rig off the weighbridge to ascertain specific axle weights.
The first weight you’ll want is the whole rig combined – this is your Gross Combined Mass (GCM). This weight should not exceed the combination of your tow rig’s Gross Vehicle Mass (GVM) and your caravan’s Aggregate Trailer Mass (ATM).
In our case, the rig was set-up with a weight distribution hitch, and in this state the tow vehicle weighed in at 1.84t and the caravan 1.46t. Combining these figures gives us our GCM of 3.3t.
Interestingly, when we weighed the front and rear axles of the tow vehicle (with caravan and load levelling bars still attached) the weight distribution was perfectly even – 920kg on each axle.
We then disengaged the weight distribution torsion bars and weighed again. The weight was 1.96t for the vehicle and 1.34t for the van. The vehicle axles were weighed in at 880kg for the front and 1.08t at the rear – meaning that 40kg had been transferred from the vehicle’s rear axle to its front axle, and 120kg had been transferred to the van’s axles.
We then attached the jockey wheel to the van and got a weight for the vehicle and van in isolation. The car weighed 1.74t Tare and the van 1.56t ATM, giving us a consistent GCM of 3.3t.
Ball weight can be deduced from these figures – the ball weight without a weight distribution hitch is 220kg. You arrive at this figure by subtracting the caravan GTM (1.34t) from its ATM (1.56t). That this 220kg has been transferred to the vehicle is confirmed with the car’s Tare increasing from 1.74t with the van to 1.96t with it hitched.
Public weighbridge tickets cost around $30 each time, so it can get expensive if you are after several weights. But if you discuss your needs with a weighbridge operator, you may be able to negotiate a lower fee.
Thanks to Macarthur Public Weighbridge, Stonny Batter Road, Minto, NSW 2566, (02) 9603 1688, and Camden Caravans, 66 Camden Valley Way, Camden, NSW 2570, (02) 4658 1929.
Source: Caravan World Jan 2011
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