Towing Vehicle Weight and Distribution

Understanding Tow Vehicle Capacities

17th December, 2020 by rvSafe Team
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Tow Vehicle Weight

Weight is one of the more significant factors which must be considered when choosing and setting up a tow vehicle for your caravan or trailer. All vehicles, when manufactured, have limits expressed for their load capacity, tare (empty except for 10lt of fuel) weight, gross vehicle mass (GVM), towing capacity, gross combined mass (GCM) and ball weight. These are strictly enforced by state and Federal laws, and any breach of these can result in the loss of insurance cover and/or warranty, as well as penalties imposed by police.

Let’s look at one of the most popular tow vehicles. A 2020 Toyota LandCruiser has a maximum towing capacity of 3500kg. That is the maximum weight which the manufacturer says the vehicle can tow, and is a figure which for any vehicle should be easily found in the vehicle’s handbook or from the manufacturer’s website.

The load your vehicle can carry — and we’ll come back to this — is the difference between the tare (empty) weight of the standard unmodified vehicle and the GVM. This will include all fuel, passengers, luggage, and any attached non-standard fittings, as well as the load imposed on the vehicle by the trailer (tow ball loading) when towing. The GCM is the maximum combined weight of the vehicle’s GVM and the aggregate mass of the trailer (the weight of the fully loaded trailer/caravan).

In setting up the tow vehicle many owners do not take into account the weight of additional non- standard fittings that many — often not unreasonably — see as necessary extras.

These can include the bull bar, winch, driving lights, roof rack, cargo barrier, rear bar, underbody guards, awning, side bars, second battery, HF or UHF radio and all sorts of other gear. In the case of our LandCruiser the tare weight is 2635kg, and the GVM is 3350kg. That leaves a load capacity of 717kg.

From that we will need to deduct the weight of two adults (if you travel as a couple, or more if you have children), say, 160kg, the weight of a full load of fuel, 130kg (138 litres less the 10L included in the tare weight), which will give us the minimum weight of the vehicle on the road and leave us with an available load capacity of 427kg.

That might seem a lot, but we must then deduct the weight of a tow bar, about 35kg, seven-pin plug for electronic controls and wiring to an Anderson plug to charge the van’s batteries while towing and a brake control unit to operate the van’s brakes (allow another 4kg) and we are down 388kg.

Your van’s tow ball/hitch weight must be accommodated, and that’s a potentially very variable figure. It should be between 7 and 15 percent of the van’s weight to ensure a stable towing platform, but if we figure on 10 percent of a 3000kg caravan GTM we have just taken another 300kg out of that remaining load capacity and we are down to only 88kg.

A bull bar can weigh up to 100kg in steel, or up to 65kg in aluminium. A winch with steel cable can weigh up to 60kg. Driving lights add, say, 5kg. A second battery (plus tray and wiring) will weigh around 38kg. A sturdy steel roof rack is up to 50kg.

As you can see, modifying a tow vehicle to suit offroad touring can add significant weight and can easily exceed the vehicle’s allowable GVM. We haven’t even begun talking about long range fuel tanks, a snorkel, second spare wheel, the contents of your glove box and centre console, seat back pockets, rear drawer sets, car fridge, cargo barrier, tools, spares, your wife’s purse, the esky of nibbles on the back seat or any of the many other items you might carry.

It’s important to understand that lighter weight options can be considered — alloy or plastic bullbars, nylon cable on a winch, choosing a lighter van (with a lower tow ball weight) — or even leaving out items that you really don’t need — such as driving lights if you don’t plan on night driving, or opting for an alloy roof rack if you don’t carry much gear up top. Don’t just fit bits because they look tough; select only what you need.

Adding weight will increase braking distance and erode fuel consumption, limit your capacities for hill climbing in non-towing offroad work or restrict you in heavy 4WD work such as in sand or mud. Try to avoid carrying items on the roof as it will impose cornering loads. Adding weight also adds stresses to the suspension, steering, brakes and tyres so expect them to wear more quickly.

My advice to anyone who’s thinking of setting up a tow vehicle is to keep it simple; it’s the old KISS principle. On my own car I just run standard shockies. Don’t go daydreaming on how many things you can fit. Fit only what you need.

Col Hughes — TJM store at Hornsby

It’s easy to see why GVM upgrades are so popular. A GVM upgrade must be undertaken by a licenced workshop using components approved by the Department of Infrastructure and Transport. For new vehicles they can be initially registered with the new figures for the enhanced GVM and will be suitable for use in all states and territories. For a vehicle that is already registered the vehicle then must be inspected by an approved engineer before reregistration with the modified GVM figure. Policies on this can vary from state to state.

Keep in mind, increasing your GVM does not increase your GCM, which remains at the manufacturer’s figure. GCM upgrades are permitted in some states but not in others, so your ability to tow across state borders may be limited. Talk to your local store.

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