Sorting out the TLAs
Words by Sean Cummins
Do you find yourself bamboozled by the prolific use of TLAs? Or wishing people would just speak plain English, as your eyes glaze over and your brain runs away to a happy place? Or – doh! I’ve done it myself. A TLA is a TLA – a three letter acronym. And given the Ozzie propensity towards short and sweet vernacular, use of the TLA is here to stay.
Vanners are not immune from these arcane utterances. And worse, three letter acronyms rule the way we are allowed to use our RVs (see, another one! Although slightly different, being a two letter acronym), so it is incumbent upon us to ensure we understand what they are.
This is particularly true when it comes to loading your trailer or motorhome. There are a number of terms you must come to grips with in order to calculate whether the mass of your trailer and tow vehicle complies with the law. Overloading can not only be dangerous, but will also likely give any insurance company all the wiggle room they need to refuse to pay you a cent in the event of an accident.
Hence, I have prepared the list below of TLAs in relation to trailer loading. Hopefully this will clear some of the fog and help you out next time you are buying a van, or loading one up.
tare |
Ok, I know it’s not a TLA, but you need to understand it before the other TLAs will make sense!
Tare weight is the weight of the vehicle before any petrol or load is added. It’s basically the lightest your vehicle can be. You need to know the tare of your tow vehicle and trailer, as this is the starting mass you use in determining how much extra weight you can add before overloading. |
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GVM |
Gross Vehicular Mass. GVM is the maximum recommended weight a vehicle can be when fully loaded. GVM is what you think about in relation to your tow vehicle; trailers use a different concept, called ATM (see below).
Knowing the tare weight (unloaded weight) of your tow vehicle and what the maximum mass (GVM) can be, you can work out how much you can chuck in and on the car; it’s just the difference between the tare weight and GVM.
Let’s say your tare weight is 1200kg, and the manufacturer has specified a GVM of 1800kg. The difference is 600kg – this is the mass of the gear you are allowed to pack, including fuel, water and passengers.
Look at your GVM very closely - it adds up quicker than most realize. 1litre of water weighs 1kg. So filling your 90 litre tank will add significant weight to your vehicle. |
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GCM |
Gross Combination Mass. GCM is the maximum allowable combined mass of a vehicle, its load, and any towed vehicles and loads; ie, this is as heavy as your tow vehicle and caravan can be when their loaded weights are added together.
Some motorhomes can also tow cars or trailers behind them; in this case, the GCM would be the heaviest the motorhome and car (or trailer) could be when their weights are added together.
For example, say the GCM of your tow vehicle is 3,500kg and its GVM is 1,200kg. The difference is 2,300kg, meaning you could whack on a trailer of 2,300kg before the GCM is exceeded.
Note, though, that this does not necessarily mean you are allowed to tow a trailer weighing 2,300kg; not unless the tow vehicle is rated to tow this mass, the tow ball is not overloaded, and the trailer has an ATM specified as 2,300kg or greater. |
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ATM |
Aggregate Trailer Mass. The total mass of the laden trailer when carrying the maximum load recommended by the manufacturer. This is the weight you would measure if you put your fully loaded trailer onto a scale.
The ATM for trailers is equivalent to the GVM of cars; they both mean the heaviest you are allowed to be when fully loaded.
You use the trailer’s tare and ATM to work out how much more you can pack on board. If your trailer has an ATM of 2,300kg and a tare of 2,000kg, then you can add an extra 300kg – the difference between the two (assuming the tow ball and tyres are also rated to carry the weight).
Look at your ATM very closely – like GVM, it adds up quicker than most realize. Again, water is the main issue; indeed, in some cases, filling a van’s water tanks to capacity can actually make it illegal to tow! |
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