How to: Outback Driving Part 3 – Corrugations and Mud

ByDean MellorNovember 25, 2020
4 MINUTE READ
How to: Outback Driving Part 3 – Corrugations and Mud

In Part 3 of our series on Outback Driving we’ll look at how to deal with seemingly endless miles of corrugations and what to do if the weather turns foul.

In ‘How To: Outback Driving Part 3’ we’re going to look at how to deal with driving on corrugations and mud, after previously discussing how to best set up your vehicle for outback driving conditions and how to correctly set tyre pressures in ‘How To: Outback Driving Part 1‘, and looking at how to deal with dusty conditions and bulldust in ‘How To: Outback Driving Part 2‘.

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Corrugations

Many unsealed outback roads and tracks are covered in bone-jarring corrugations and, unless you’re prepared, these can be almost unbearable.

Corrugations are formed on unsealed roads as vehicles drive over them. As a vehicle’s wheels hit small bumps on the road surface, they move up and down, leaving higher ridges where the wheels move up (less pressure on the road surface) and compressing the parts of the road where they move down (more pressure on the road surface). As the corrugations begin to form, the wheels of following vehicles also oscillate up and down, forming bigger and bigger corrugations. This is why unsealed roads need to be regularly graded, to smooth out the corrugations (and the potholes) formed by vehicles that drive over them.

Of course, driving over corrugations can feel extremely uncomfortable as your vehicle’s wheels oscillate over the bumps, but there are ways to ‘smooth’ them out. If your vehicle’s tyre pressures are too high when driving over corrugations, it will try to shake itself to bits, and you and your passengers will not enjoy the journey at all. By lowering tyre pressures, the tyre sidewalls will have more flex and will more easily be able to soak up the bumps in the road surface. If you run, say, 35psi on the road, try dropping your tyre pressures to around 28psi on corrugations – ride quality will improve markedly. Bear in mind, however, that the more you lower your tyre pressures the more you will have to slow your speed, as the more the sidewalls flex the more heat they will generate. This can be problematic, as explained in the article 5 things you may not have known about tyres…

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While tyre pressures are key to comfort and vehicle control when it comes to driving over corrugations, vehicle speed is equally important. I’ve seen people driving along corrugated roads at a snail’s pace when they should have been driving at 80-90km/h, and I could only imagine how awful it must’ve felt inside. As corrugations vary in height and frequency, the ideal speed on one corrugated road will not necessarily be the same as another corrugated road. The best technique is to adjust vehicle speed until you find the sweet spot, where your 4X4’s tyres are able to skip over the top of the corrugations from one peak to another, rather than dropping into each trough. This might be 80km/h, 90km/h or even 100km/h, depending on your vehicle and the height and frequency of the corrugations. Once again, remember to not go too fast if you have dropped your tyre pressures.

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Wet Weather

Yes, it rains in the outback, and when it does all those dirt roads out there turn into a muddy mess. Well, not all of them; decent gravel roads with good drainage can cope with a fair amount of rain, in which case you’ll simply need to drop your speed to suit the conditions, but on crook dirt roads with poor drainage, rain can present serious challenges, especially in flat, outback country. This is why many outback roads are only suitable for use in dry conditions and are closed when wet. When water is unable to quickly drain away, or when bulldust patches fill with water and become a sloppy quagmire, road damage occurs when vehicles drive these roads.

Never drive on closed outback roads. Obey all relevant signage and if unsure of the status of a road check with local and/or state road authorities… or ask at the local pub.

If you find yourself on an open outback road when it’s wet, driving through mud can be tricky. Momentum will be your friend in these conditions, but go too fast and it can be your enemy – don’t drive so fast that you could lose vehicle control. Select the appropriate gear and stay on the throttle in muddy sections, and let the vehicle fall into existing tracks (unless they’re too deep) because the base of the tracks is likely to be firmer from being compacted by previous vehicles.

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The black soils found around rivers and creeks can be extremely slippery when wet, so avoid them if at all possible. Lowering tyre pressures can help with traction when driving in mud, but don’t go so low that you the tyres could spin on the wheels or peel off the rims. When driving in muddy conditions, you may have to regularly get out of your vehicle to clear mud away from inside the wheel arches, or from inside the wheels (mud stuck to wheels can throw them out of balance). Also make sure your vehicle’s cooling system (grille/radiator) isn’t blocked by mud, ensure the alternator is clean and that headlights/taillights aren’t obstructed by mud. Oh, and top up your windscreen washer bottle.

If you’re driving in the outback, hopefully you’ll be carrying appropriate recovery gear. Handy items for mud driving include a shovel, recovery boards, snatch strap, tow ropes and a winch.

Next week…

In ‘How To: Outback Driving Part 4’ we’ll take a look at desert driving and all the gear you’ll need for the big outback trip. Keep an eye out for it…