DRIVING/TOWING - TOWING
Before you buy a towing vehicle you need to make sure that it can do the job. Don’t rely solely on 4WD makers’ claims about permitted trailer weights, because in many cases they have small-print conditions attached.
Many 4WD owners think that a vehicle can be loaded to its rated gross mass (GVM) and, at the same time, tow a braked trailer that weighs up to the maximum gross trailer mass (GTM) allowed by the vehicle maker. That’s wrong in almost all cases.
The major limiting factor is the tow vehicle’s gross combination mass (GCM) rating, which is the total permitted weight on all vehicle and trailer axles when the loaded vehicle and loaded trailer are connected.
With very few exceptions this GCM rating is always less than the total of the tow vehicle’s GVM and the trailer GTM.
Typically, a 4WD’s GCM rating is 400kg to 800kg less than the sum of the vehicle and trailer axle weights.
This means that if you plan to load the towing vehicle to its maximum GVM, let alone a legally increased GVM, you cannot tow a trailer that vehicle is rated to pull. The trailer GTM needs to be lighter, by a typical 400-800kg.
The alternative is to ensure that the towing vehicle weighs that same 400-800kg less than its rated GVM, if the full trailer weight is being towed. In many cases the towing vehicle will have to be virtually empty to pull its rated trailer load.
We think that the trailer ratings put on their vehicles by 4WD manufacturers should be much clearer than simple bald statements about trailer GTM. The
GVM-GCM trade-off should have to be stated as well.
Most 4WD wagons have a payload rating around half a tonne to 750kg and 4WD utes have a nominal one-tonne-plus payload rating, but that ‘payload’ includes the weight of the people on board, fuel and aftermarket equipment.
To get a real-world 4WD tare weight you need to add: bigger tyres all around and a second spare wheel and tyre (40kg); ‘roo bar with a winch (50kg); a second battery (30kg); tow bar (10kg); full long-range fuel tank (140kg); tools (10kg); spare parts (10kg); recovery kit (10kg); full fridge (50kg); food boxes (10kg); clothes (10kg) and two adults and two kids (210kg).
That’s a total weight of nearly 600kg that needs to be added to the tare weight, before you can calculate your real-world payload capacity!
Moving from a wagon to a ute may solve tow vehicle weight issues, but it’s not necessarily the case.
It’s obvious that your 4WD may well exceed the maker’s GVM if you total the manufacturer’s tare weight, the weight of the gear listed above and the towball weight of a heavy trailer.
Even if your loaded towing vehicle doesn’t exceed the vehicle maker’s GVM there’s a chance that the front or rear axle mass limit may be exceeded, because of too much weight on the front or rear axle.
An example is that some 4WDs overload their front axles – even when they’re empty – if a steel winch bar, side rails, winch and second battery are fitted. Others overload their rear axles with only a modest amount of freight in the back, but with a heavy ball weight on the towbar.
One way of transferring rear axle towball weight is to use weight distribution bars on the hitch, but this needs to be done carefully: not so much weight transfer that there’s a risk of damage to the vehicle’s towbar and chassis, or front axle overload.
To illustrate the points we’ve made, let’s look at some current ute offerings: Ford Ranger, Nissan Navara and LandCruiser 70 Series.
All three utes have a trailer mass rating of 3500kg.
The Ranger has a GVM rating of 3200kg and a GCM rating of 6000kg.
The Navara has a GVM rating of 2910kg and a GCM rating of 5910kg.
The LandCruiser has a GVM rating of 3300kg and a GCM rating of 6800kg.
It’s obvious from the above figures that the only one of these three that can be loaded to its GVM and still legally tow a 3500kg trailer is the LandCruiser. Its 3300kg GVM plus trailer 3500kg GTM adds up to the vehicle’s permitted 6800kg GCM (3300+3500=6800).
On paper, the Ranger looks like the next best, but if the Ranger is at its GVM its trailer capacity drops to 2800kg (3200+2800=6000), while the lighter Navara at GVM can tow 3000kg (2910+3000=5910).
Another consideration is axle capacities: vehicle makers used to allow a considerable margin between the sum of the axle ratings and the vehicle’s rated GVM. The LandCruiser continues this practice, having a combined axle capacity of 3780kg, which is 480kg greater than its 3300kg GVM.
In contrast, the Ranger’s and Navara’s total front and rear axle capacities are only around 100kg above their vehicle GVM ratings. The ‘Cruiser also has a much higher rear axle rating (2300kg) than the Ranger (1850kg) and the Navara (1700kg) and it’s the rear axle that has to handle most of the imposed load.
You need to do your sums carefully before you invest in a 4WD tow vehicle or a heavy trailer. The two have to work in concert.