Wet weather and four-wheel-driving

4WD Tips      July 23, 2014      David Wilson

Well we’re in the soggy depths of winter and winter of 2014 has been especially wet in South Australia. With the reservoirs full and the ground sodden any 4WD excursion is likely to be a pretty slippery affair.

Let’s take a look at how you manage those conditions from a driver’s perspective including the obvious and not quite so.

From the driver’s seat the windscreen is mightily important. Without clean glass your vision will be impaired. I’m often surprised at how poor some drivers let their wipers get before doing something about them. For around $20 a simple and quick fix can be obtained, snapping out the old and replacing it with the new and a clear view of the road ahead.

1 Wiper Replace

Additionally with so much humidity in the air it doesn’t take long for the confined space of a vehicle’s cabin to become all fogged-up. Another simple fix that won’t cost you a cent is to use your air-conditioner. Set the vent to the windscreen, turn the AC and fan on to a low setting and recirculate and within moments the interior fog will lift from the windscreen and side windows leaving you again with clear vision. Set the temperature to a desirable level to keep warm without being over-powering (too hot and you’ll likely increase the risk of fatigue on a longer journey – can’t get too comfortable).


Under the bonnet its good policy to keep the windscreen washer reservoir topped-up and with a dash of detergent too, to remove road grime and bug splatters.
On the highway you want to pay attention to how the road has been affected by the passage of heavy transport. In periods of heavy rain water will “pond” in the tyre grooves, worn into the bitumen by constant heavy traffic. That patch will pose a threat to your grip levels and on a bend might mean a momentary loss of traction.
Modern vehicles with ETC (electronic traction control) will be able to respond immediately to the threat, whereas the rest of us will have to make that adjustment by getting off the accelerator for a moment. Heavy use of brakes isn’t advisable either on a non-ABS (anti-lock braking system) vehicle in this situation as the front wheels will lock and render steering non-existent.

In a non-ABS situation you’ll need to employ the art of “threshold” braking (braking firmly but not beyond that fine point of lock-up and maintaining a constant pedal pressure). Of course in an ABS vehicle it’s simple, push the brake pedal HARD and let the electronics work out what’s required.

On dirt it’s really a case of keeping the speed in check. On local dirt that’s well maintained and sheeted with a gravel/metal that offers some grip it’ll be manageable. We have been telling all our clients that 80km/h is the maximum speed on dirt, but that’s only if the road will support it on that day. The real speed will likely be considerably less. What will help enormously is the use of HIGH range 4WD instead of just 2WD on a part-time 4WD and if you’ve got a constant 4WD, locking the centre-differential will help achieve double the grip.
On Outback dirt it gets more complicated because often the road will be clay-based and when wet that’ll become super-slippery. Additionally in desert areas the road often sits lower than the surrounding land, as the road-makers come past annually and flatten the corrugations out but gone down a little deeper each year. In torrential rain those roads become creeks.
Outback roads are closed in heavy rain situations and can stay that way for days after the event. Contacting the SA Department of Transport’s “Far Northern Road Report” is a good way to check on the current state of the network and where you can and can’t go. Here’s the link http://www.dpti.sa.gov.au/OutbackRoads

1 4WD Light

On any sort of dirt we’re firm believers in the benefits of tyre pressure reduction. On the made dirt roads in good condition that maximum speed of 80km/h might be accompanied with a 20% reduction in pressure from the placarded (the sticker on your door pillar) pressures set by the vehicle maker. This affords the tyre greater impact resistance, meaning less likelihood of punctures and much shorter braking distances coupled to better steering.

If it were really wet on one of those clay roads we often use a 50% reduction in pressure achieving two things, mobility and no track damage. A 50% reduction in pressure needs a 50% reduction in speed though. You’ll need to reinflate to the highway pressures once you resume on the bitumen.

There’s a fair chance too that one day you’ll come across a flooded creek that intersects a track. That is fraught with some peril, and if it can be avoided, do so. It’s much better to suffer the inconvenience of a detour, than never coming home again. If another vehicle can demonstrate that the crossing is possible and it’s safe, then proceed if you must.

Most vehicle makers get pretty nervous if the water depth exceeds axle height. That could be as little as 400mm. You might want to get the owners handbook out to check what they say.
Don’t despair, spring is just around the corner and the promise of some sunshine is near. Drive safely!

1 Wet Outback Road

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