DIRTY DANCING
Australia has millions of kilometres of dirt roads, and they take you to the best places you can imagine.
Yet taking them too lightly could land you in trouble
Every great 4WD track in Australia sits at the end of a dirt road. In fact, some of our most-loved 4WD tracks are just that - dirt roads. Take the Birdsville Track f’rinstance; dirt road – and a pretty good one at that. Cape York? At the end of a bloody long dirt road. Gibb River Rd? You guessed it, a spectacular dirt road, where you’ll hardly ever have to shift into low-range. So, while we all love using those reduction gears and that little stubby lever, the fact of the matter is we’ll probably spend more time on high-speed dirt, than in low-low. When travelling at speeds faster than a crawl, the chance for damage increases big-time.
4WD HIGH OR 2WD?
Whether to shift your 4WD into high-range 4WD with the centre diff locked, or leave it in 2WD (if you’ve got the option), is an often misunderstood technique of 4WDing. This is probably a hangover from the old days, when we all used to avoid the dreaded ‘diff wind-up’ like the plague. Now days we know a little more about our 4WD systems, and it’s widely accepted that using 4WD is the way to go on most dirt roads. I say ‘most’, because the dirt road surfaces around Australia vary dramatically, from dry, baked, hard clay, to slippery gravel and bull-dust.
But back to 4WD vs 2WD. Having all four wheels driving gives you more traction, so when you’re exiting dirt corners, the front effectively ‘pulls’ the vehicle around. I’ll probably still receive some hate mail from those who believe that using 4WD on the dirt increases the wear and tear on your vehicle, and it does. But I’d rather be safer than have some extra wear on my fourby. And you’ve got to remember that as soon as you hit the blacktop, you need to unlock the centre diff.
The great thing about splitting the drive 50 percent to the front and rear axles, is that you’re less likely to have the back-end step out in a power slide. This happens when you’re accelerating while negotiating a bend, and the back wheels lose traction due to too much power being applied; the technical term is ‘acceleration oversteer skid’, and it’s far less likely to happen in 4WD, because the power is spread over all four wheels.
The other type of common skid you have to deal with on the dirt, is the front-wheel understeer skid. Drive into a bend too fast, and the vehicle wants to plough straight ahead, no matter how hard you steer. The solution here, is to slow down by reducing throttle pressure, and if need be, gently apply the brakes while keeping your steering wheel pointed where you want to go.
There are a couple more skids you need to become familiar with when you’re on the dirt. One is the high-speed oversteer skid, which occurs when you take your foot off the accelerator half-way around a bend, and the back end loses traction and tries to overtake the front. The solution here, is to apply the accelerator again just enough to gain traction, and steer your way out of the corner. And lastly, there’s the braking skid. This is where you lock up all four wheels to stop in a hurry. It’s surely the fastest way to stop, but you do lose all steering. If you need to steer - and stop - release the brake pedal just enough so that the front wheels can point you in the right direction. |
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CORRUGATIONS
Aussie corrugations are surely the world’s best...or worst. They’re deeper, longer, and more damaging to your fourby than many other terrains. They kill shock absorbers quicker than any other surface, and they’ve even been known to shake the whole dashboard out of fourbies. As your wheels bounce up and down over the mini-mountains, they shake the bejezus out of your vehicle. Modern 4WDs can handle corrugations quite well – in fact they can travel at 100 km/h over the ruts easily. And that’s the advice that most experienced four-wheel drivers give to novices. They’ll say: “Yeah mate, 100 to 110kph smooths out the corrugations no end!”
And they’re right, you get a much smoother ride as your fourby dances over the top of the corrugations, rather than bumping and crunching slowly over each and every lump. But what they don’t mention is that at higher speeds, your suspension is working a lot harder. It’s for this reason that places like Cape York, with its hundreds of kilometres of corrugated roads, will sort-out many a suspension system. It’s usually the shock absorber that feels it, because a shock is essentially a ‘heat pump’.
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It transfers the energy of the wheel bouncing up and down into heat, but it can only do that effectively to a point. When it gets too hot (usually due to not enough capacity or poor valving), the oil inside the shock begins to aerate or foam, reducing its effectiveness. The solution here, is to stop, wait for your shock absorber to cool and recover, then move on. That’s twin-tube shocks, by the way. Mono-tube shock absorber (like Bilsteins) tend to stiffen when they are stressed, so understand what is under your truck.
If your shock absorbers do fail, you’ll have to seriously limp your vehicle home. With even one shock absorber not working properly, driving at high speeds is downright dangerous. The only exception to this rule is leaf sprung vehicles. Here, shocks are less important, as the friction between the leaves tends to do some of the job of the shock absorber. Coil springs and live axles are a different game altogether though – I once limped a Jackaroo back from the Cape with two stuffed rear shocks – and I’m lucky to be here today, I reckon. I sure know why many serious travellers go for big-bore or remote-canister shocks.
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