It is important to be aware that many manufacturers have specific conditions for their vehicles when used for towing. You need to refer to your vehicle manufacturer’s handbook, before towing – and even before buying a vehicle as the cost of additional or mandatory vehicle equipment may influence your buying decision. Always adhere to the conditions set by the manufacturer for towing with your vehicle – as failure to do so may void your warranty, cause mechanical damage or even result in an accident where you may possibly not be covered by your insurance.
Loading your vehicle
Unladen (empty) weight : This is how much your vehicle weighs when empty, referred to as kerb weight and tare weight depending on the manufacturer. ’Tare’ means empty but with water in the radiator, all of the lubricants on board and a token amount of fuel. ‘Kerb’ means all the fuel on board and sometimes 75kg added for the driver – although some manufacturers use their own definitions for this weight, and there is no universal standard. For all practical purposes both terms refer to an empty vehicle.
Gross Vehicle Mass (GVM) : This is the total allowed weight of the vehicle – including all the passengers, fluids, equipment – everything except the weight of the trailer, and is specified by the manufacturer.
So – for your vehicle, get the GVM and subtract the unladen weight, and the difference will be the amount of weight that you can load into your vehicle (payload capacity).
Trailers have tare weights and gross weights as do vehicles. Tow capacity is the GVM or gross weight of the trailer.
Towing and Loads
If you are towing a trailer without brakes, the maximum tow capacity of your vehicle as per your manufacturer’s handbook will refer to the GVM of the vehicle plus the GVM of the trailer – ie the weight of your vehicle fully loaded including passengers plus the weight of your loaded trailer.
If you are towing a trailer with brakes such as a caravan, the maximum tow capacity specified will refer to the heavier of the GVM of your vehicle and the GVM of the item being towed.
Obviously, it is probably not a good idea to load your vehicle to maximum payload, and then hook up a trailer that is at the upper limit of the tow capacity. A specification called Gross Combination Mass (GCM) deals with this risk – this should be defined in your vehicle handbook.
Towball download is the download limit specified by your vehicle manufacturer – this is the actual load that is imposed by the trailer in its most heavily loaded state. Specialist tow places or public weighbridges can measure this for you. This is important especially in Australia, where we generally get trailers designed for a 10% download, which may mean that fully loaded, trailer may exceed your vehicle manufacturer’s limit.