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It sounds like stating the obvious, but you will observe that not every caravan is correctly loaded and hitched, putting themselves and other road users at risk.
The Caravan and Camping Industry Association has a useful guide to towing on Towing Guide. Additional towing advice sites can be found in the Links section here
The basics are:
Do not exceed the load weight
specified for your caravan
Do not exceed the weight your tow vehicle is rated to tow
Do not exceed the total gross combined
weight (fully loaded car trailer and yourselves) your tow vehicle is rated to tow
Do not exceed the tow ball weight your tow hitch is rated to tow
For all of the above points, when planning your rig and tow vehicle, allow a good margin for error. There are sure to be times when you will add a bit more to your load.
Where to find a weighbridge so you know your weights? See Public Weighbridges
Where manufacturer’s specifications of the vehicle are not known, then the maximum weight that can be towed is either 1.5 times the loaded mass of the vehicle (if the trailer has brakes) or, if the trailer has no brakes, the weight is limited to the unloaded mass of the vehicle. However it would be unwise to travel with a trailer which outweighs the tow vehicle as recommended hereunder.
Keep the heaviest items central in the trailer (ie over the wheels)
Do
not add heavy items such as tool boxes on the back or front of your caravan, unless done at the construction of your caravan and allowed
for to maintain a balanced rig, or done under the guidance of a suitably qualified engineer.
A further recommendation is that the laden weight of your trailer doesn’t exceed the laden weight of your tow vehicle, even if it is within legal limits. It is a simple game of tug-o-war and you need to be in the winning side if something goes wrong. Simple swaying of the caravan can result in the whole rig being taken off the road or a rollover if the caravan is the heavy end.
A weight distributing hitch is highly recommended. Weight distributing hitches transfer some of the load from the rear of the vehicle to the front, distributing weight evenly to all wheels for safer towing.
This video explains the difference between levelling the load visually with air bags, and distributing the weight with a Weight Distribution Hitch.A simple demonstration
of the yaw (swaying effect) on a caravan or trailer. Watch here
Rob Caldwell has published Caravans and Trucks Sharing the Road which explains the effects of a truck passing or overtaking on airflow and caravan stability.
Collyn Rivers has excellent information on his website explaining vehicle dynamics here and a e-book onWhy Caravans Roll Over And How to Prevent It.
To check what a vehicle is permitted to tow, including GVM and GCM and other specifications, visit Red Book. This Beadell's Tours link can be used as a quick guide, but bear in mind there may be differences between year models and dates back to 2015.
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TARE / Kerb Mass / Tare Mass |
is the unladen weight of the vehicle or trailer/caravan |
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Simply put: TARE is
the base weight of the empty trailer/caravan at manufacturer and may be stamped on the VIN plate and will be shown on the registration
papers |
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GVM / Gross Vehicle Mass |
is the total allowable weight of the vehicle including its load |
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Simply put:
GVM is the maximum allowable weight of the vehicle and its load, which includes yourselves and any tow ball download weight when trailer/caravan
is attached. GVM is specified by the vehicle manufacturer |
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GCM / Gross Combination Mass |
is the total allowable weight of
a loaded vehicle and its loaded trailer |
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Simply put: GCM is the maximum allowable weight of the vehicle and trailer combination,
including their loads, and is specified by the vehicle manufacturer |
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GTM / Gross Trailer Mass |
is the allowable weight supported
by the axle/s or wheels of a loaded trailer when attached to the tow vehicle |
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Simply put: GTM is the maximum allowable weight
supported by the axles and wheels when the trailer/caravan is attached to the tow vehicle, as specified by the trailer manufacturer
and maybe stamped on the VIN plate |
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ATM / Aggregate Trailer Mass |
is the total allowable loaded weight of
a trailer including the tow ball download weight when not attached to the tow vehicle |
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Simply put: ATM is the maximum allowable
weight of the fully loaded trailer and is specified by the trailer/caravan manufacturer and is stamped on the VIN plate |
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Tow Ball Weight
/ Tow Ball Mass / Download |
is the weight transferred by a trailer onto the rear of a tow vehicle |
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Simply put: This is
the weight applied to the tow ball/hitch of the vehicle by the trailer/caravan. This weight will vary according to how the load
is distributed within the trailer and needs to be within the limits specified by the vehicle tow bar manufacturer and/or vehicle manufacturer.# |
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Payload |
is the weight that is permissible to add to your trailer, including water, gas and anything added after the TARE
was established. This is specified by the manufacturer and may be stamped in the VIN Plate |
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Simply put: This is the maximum allowance you have for loading into/onto to your trailer/caravan. It is the difference between the TARE ## and ATM as shown on the VIN plate. By the time you fill your water tanks and gas bottles you may have a very limited allowance for your packing
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# Note: If a ball weight is stamped on the trailer VIN plate it will generally have no relationship to the actual ball weight when the trailer/caravan is loaded. However, when a trailer manufacturer specifically stamps the VIN plate with a Maximum Ball Weight then this must not be exceeded.
## When you purchase your caravan, be it new or second hand, it may exceed the plated TARE (weight when it left the
manufacturer). This may be in the case with a new caravan when additions such as annexe and/or batteries have been added
by the dealer. When purchasing second hand, additional items added the previous owner/s will increase the empty weight.
The TARE is plated and does not change, but the increase in the caravan's empty weight will reduce your payload allowance.
Hint:
Whether you are purchasing new or second hand, ensure that the caravan, when ready for you to take delivery, is weighed
and that you have an adequate payload allowance. Have this payload requirement specified on your contract to purchase, and have
the purchase conditional on this. Too many people have purchased a caravan, then found they have little or no payload allowance.
Many caravan manufacturers follow an old rule of thumb, giving a difference between TARE and ATM as 300 kilogrammes for a small single axled caravan, and 400 kilomgrammes doe a larger dual axled caravan. With modern caravans having a number of water tanks to provide for an inbuilt shower and toilet, filling the water tanks can leave little or no room in the payload allowance if adhering to the old guide. For example, filling the water tanks on a caravans with 3 x 100 litre water tanks will add 300 kilogrammes which forms part of your payload.