Conquering the Corrugations
badly corrugated dirt road

It won't be the gnarly hills, flooded creek crossings or axle deep sands of Australia that test the endurance of your vehicle but the gutted corrugations of the roads that lead to many iconic outback destinations.

It's these corrugations that will see mirrors rattle apart, aerials come adrift, roof racks rub through paint and the contents of your camping kit eventually disintegrate until they resemble nothing of the finely organised package that you started with.

There are a hundred theories on how dirt roads become corrugated and they encompass everything from over-zealous truck drivers, to braking too hard before corners, to overloaded vehicles and over inflated tyres. Regardless of how corrugations form driving on them is uncomfortable and eventually shakes your car to pieces.

If you plan on travelling the backroads of Australia then you are going to encounter endless kilometres of corrugated dirt roads but you can take a few measures to reduce their bone-rattling affects.

Get Your Tyres Down and Your Speed Up

It's not often that you're advised to go faster during an unpleasant driving experience but it is fact when driving over corrugations that 60kph may be a lot more comfortable than 30kph and 80kph - 90kph may be even better. We aren't suggesting you belt around the bush at 140 because when you eventually put your car on it's roof - you'll blame us, but there is a distinct speed that is 'right' for every vehicle.

The key is to synchronise all the elements of your car with the corrugations - the pressure in your tyres, the weight of your car and its suspension and handling characteristics. Finding the best speed for your particular vehicle will that see these variables all align in some sort of harmony that sees you floating on top of the corrugations rather than rattling between them.

Of course this increased speed and increased comfort means your tyres are spending less time in contact with the road. Be aware that too much speed will cause the vehicle to 'drift'. Driving over corrugations requires finding a balance between comfort and control.

Tyre Pressure is Everything

Reducing tyre pressure turns your tyres into big cushioning shock absorbers that soak up the bumps and smooth out the ride.

The is no golden number for the correct tyre pressure for either bitumen or dirt roads. Each vehicle is different and each tyre is different. Inflation pressure should be adjusted to load. A big fully laden 4WD may require as much as 45psi in each tyre to accommodate the load while a small city commuter may find 28psi is all that's required.

As a general rule of thumb try decreasing tyre pressure for corrugations by about 20 percent. If you're running 40psi on the bitumen try 32psi for corrugations or if you normally run 32psi try deflating to 26psi.

Lower tyre pressures and high speed creates heat build up in tyres which can cause damage or premature failure. Under-inflation can also cause tyres to 'roll' off the wheel when cornering. Don't reduce so much pressure that the tyres look flat. Just a slight bulging of the sidewalls is fine.

Pick Your Line

Corrugations are worst where people brake or accelerate. For instance: the entry and exit of corners, the crests of hills or the entry to river crossings.

Outback roads often run through wide open expanses where visibility extends for miles and on-coming traffic can be seen well in advance. There's no need to slavishly 'stick to there left' if it means you must drive on the worst sections of the road. Pick the smoothest line and anticipate badly corrugated sections by the changes in the road. By anticipating the changing conditions you will slow down naturally where required, without braking, and create a smoother ride.

2WD or 4WD?

When employees of mining giant BHP Billiton are travelling on dirt roads they are instructed to travel at 80kph maximum with headlights turned on and the transmission selected to 4WD only. They are often required to have attended a 4WD drivers training course prior to driving on dirt and will have to phone in when reaching or departing their destination. They may have to stay overnight if a return journey means travelling after 6pm in fading light or if they will drive for more than six hours in any one day. BHP would have everyone living in nappies if it could.

Fortunately we don't all work for mining giants and the choice to drive in 2WD or 4WD is ours.

Logic says that 4WD is the safest and most stable method of traversing loose dirt roads and in reality it probably is. Of course not all corrugated roads are slippery gravel or powdery dust and hard-packed, well compacted dirt byways can offer similar levels of traction to that of bitumen.

Our preference is to travel in 2WD on corrugated or dirt roads that don't require the extra traction that 4WD affords. We find that 4WD 'pulls' the car around the corners and fastidiously holds it's line where the slight looseness of 2WD makes for a less fatiguing ride. It's just personal preference. If safety is paramount then select 4WD.


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