Wednesday, Dec 05, 2012 at 18:42
Quote "remind me again why if you have the correct tug and matching van do you need a WDH?"
Well for starters Ford, Holden, Mitsubishi and Toyota either recommend or require WDH to be used, particularly for heavier towing loads.
The tow ball is mounted at a distance of around 50% of the wheelbase behind the rear axle centre. The older Discos are over 60% and the newer ones are a lot less. Working on an overhang of 50%, If you load 300 kg on to the ball you will lighten the front axle by 150 kg. So where does that 150 kg go to, it is transferred to the rear axle. That means we now have 450 kg of loading on the rear axle. Many large vans will have a 300 kg or more ball weight if they are going to be stable.
Now look at a specific vehicle. The Landcruiser 200 series is a particularly popular tug. The various models have a spread of tare weights, lets take an average - 2680 kg. The GVM is 3300 kg, leaving a loading allowance of 630 kg. When loading vehicles very little of the load goes onto the front axle. So we now load the vehicle most of the weight going on the rear axle. A likely load will be 2 x 80 kg driver/passenger (160 kg) 82 litres of fuel (82 x 0.745 = 62 kg) and the 450 kg imposed by the ball weight if we are not using WDH. This makes a total of nearly 670 kg on the rear axle. If the 450 kg was a load distributed in the cab with the rear seats folded a little would be imposed on the front
wheels and you would not have that 150 kg removed from the font
wheels.
How much is that going to overload the rear axle? If you put any more loading in the tug the rear axle will certainly be overloaded. Every Cruiser 200 with a tinny on top will certainly be overloaded if there is no WDH fitted.
The big exception where WDH is not required is the Patrols. We all know that Nissan says that WDH is not recommended with their tow bars (even though they have WDH as accessories on their USA web sit for the same vehicles.) However they specify GVM reductions for the higher ball loadings. For example, in the GU Y61 wagon the GVM is reduced by 300 kg. Similar GVM reductions should also be applied to other vehicles if you are not using WDH. If you took 300 kg off the Cruiser you would not have much allowance for the fuel and you would have to leave the
cook at home.
If you are towing heavy loads you need a WDH to shift the apparent point of your drawbar load further forward than the tow ball.
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