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How When Why << Back
BEFORE YOU GO OFF ROAD
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Before you head for the back country you must spend some time finding out more about the special features of your 4WD and some necessary techniques.

GROUND CLEARANCE

An important part of getting to know your vehicle is taking a look underneath. I don’t mean taking it to a garage and putting it up on a hoist. Rather, get down on all fours and have a really good look down the length of the underside.

All 4WDs have some parts that protrude downwards. There are suspension parts, steering gear, bash plates, the sump, gear boxes, exhaust systems, diffs, prop shafts, brake components, fuel tanks, door sills and steps, tow bars, protection bars, chassis cross members, pipes, hoses, wiring, trailer light plugs etc. – all the vulnerable bits that are likely to get damaged if you drive over a rock or a tree stump hidden in the grass, under water or in mud holes. Getting to know where all these are may seem like a waste of time but it may save you a very large repair bill if you can avoid hitting any sensitive part of your vehicle’s anatomy.

It could also mean the difference between getting somewhere or getting stuck. The ability of a 4WD to clear a given obstacle is dictated by three rather obscure-sounding angles.

These angles set the physical limits of your vehicle and there is not much that can be done to change them. The approach angle describes the maximum incline you can drive onto. The ramp angle restricts the maximum size of any ridge or hump you can safely drive over. The departure angle dictates the steepest hill you can drive off without the vehicle becoming stuck.

The departure angle is perhaps the only one you can have any effect on. Tow bars, especially those fitted with drop plates to adjust the height, can seriously interfere with the departure angle. Consider whether these are absolutely necessary or whether they should be removed for serious off-road use.

STEERING YOUR 4WD

You may think that steering your 4WD is just like steering your car but it is not. First of all you are in charge of a much bigger and heavier vehicle, which is more like a truck than a car. Even if the vehicle has power steering you need to keep two hands on the wheel to keep proper control and be able to take evasive action in the event of an emergency. If you have sliced a tyre sidewall partly through on a rock when you are travelling slowly off road the tyre will warm up and pressures will increase when you are travelling at normal road speed. The tyre can deflate suddenly and if you have not got two hands on the wheel you could easily lose control of your 4WD. On a rough or rutted track the vehicle can take off to wherever it wants to if you are not hanging on to the steering wheel with both hands. There is no way you can control your 4WD properly with one hand draped casually over the wheel. The arm out the window on the ledge or the hand gripping the gutter is not good practice either. Not only is it unsafe, but in the bush you run the risk of insect stings and severe scratching.

Don’t wrap your thumbs around the steering wheel – keep them on the outside. If a front wheel hits a rock or log, the steering wheel can spin from lock to lock in a second, and if your thumb gets caught by a spoke you may be driving home with a broken thumb or even forearm.

Steering your 4WD off road is an art and you need to be more precise because there is less room for mistakes on narrow tracks. Practise your wheel placement by placing rocks on a grassy paddock and then driving over them, making sure that each tyre on each side of your 4WD actually rolls over the rock. You will be surprised as to how difficult it is to know exactly where each tyre is in relation to the ground.

You must remember that when turning a corner going forwards that the rear wheels of your 4WD take a tighter line than the front wheels and can drop over a bank or hit that sharp rock on the track edge if you don’t allow for it. The steering lock on vehicles can vary and if you put wide tyres on it may be decreased and it may take several goes to get around a sharp corner.

Remember too that if you are on a slippery surface with the brakes on you will not have any steering. You can only steer a vehicle if the wheels are actually going around.

Losing traction with front wheels in a 4WD is fairly common on slippery clay tracks, even at slow speeds, despite the wheels being turned in the required direction. Steering effect can be totally lost when neither of the front wheels has sufficient grip on the track to do what the driver wants. When the front of the vehicle doesn’t go around the corner, or on the line the driver intended by steering, the effect is known as ‘understeer’.

In slippery conditions, if the vehicle has too much momentum or speed (or just more than the friction of the small contact patch between tyres and ground can manage) it tends to keep going in the same direction that it was before the wheels were turned. Inappropriate tyre tread pattern, wear or incorrect pressures don’t help here either. Gravity pulls things downwards. If the slippery track slopes both downhill and off to one side, then, without positive traction, that’s where the vehicle will try to slide. This can happen relatively easily in 2WD when only the rear wheels are driven. If the vehicle is in 4WD the effects are often noticeably reduced because the vehicle has better and more positive ground contact when all wheels are driving.

Where you are faced with driving along a difficult track where precise steering is required to keep you out of trouble it is advisable to make use of a marshal. He can stand beside your 4WD, watch the wheels and give you instructions like ‘left hand down’ or ‘right hand down’ or even ‘stop’. You will have to concentrate on the steering, take the word of the marshal as the truth and not make assumptions for yourself. They can see your wheels and you can’t.



 
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