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The 20 per cent rule

A simple tip every driver should know

When it comes time to swap tarmac for the outback, correct tyre pressures can be a matter of some debate.

Getting stranded in the bush is a possible outcome of bad pressure management, so it pays to have a simple formula top of mind to get the best from your tyres.

Adventure 4WD owner and professional off-road instructor David Wilson recommends what he refers to as the 20 per cent rule.

The rule is simple: when you make the transfer from bitumen to dirt, drop your tyre pressure 20 per cent, and reduce your speed 20 per cent.

So if you were running 36psi, drop your tyre pressure down to 29psi, and if you were travelling at 100km/h on bitumen, choose a safe speed for the conditions with a maximum of 80km/h.

David Wilson Toyo Tires off road driving tyre pressure management

David Wilson explains the logic.

“The concept of the 20 per cent rule came about because we noticed that in outback situations a lot of people experience tyre failure after tyre failure. These are almost always caused by overinflated tyres.”

“There is a furphy about pumping tyres up in gravelly or rocky conditions, with the idea that hard tyres will deflect punctures.

“This couldn’t be further from the truth. The reality is that when they are pumped up hard, a rock or sharp point will go straight through a tyre.

“We needed to find a median pressure that allows drivers to travel at a good clip on the gravel while maintaining the flexibility to absorb impacts,” he says.

“After doing some practice with tyre pressure monitoring systems that also record temperatures, we worked out that if you reduced tyre pressure by 20 per cent from the recommended pressure tyres won’t run hot, they gain some puncture resisting flexibility and allow a maximum speed of 80km/h.”

off road driving toyo tires open country tyre pressure management

David also strongly recommends staying below 80km/h at all times off-road.

“You should never go faster than 80km/h on dirt. Dirt and gravelly roads are far too unpredictable and that means your grip levels are unpredictable.

“Pushing above 80ks means you are flying with the angels.

“On corrugations you are hitting all the high points. If you hit a pothole going through a bend, an understeer or oversteer situation will quickly see you a part of the scenery.”

While we were at it, David offered us another off-roading gem.

off road driving toyo tires open country tyre pressure management

“While on the dirt try engaging high range 4WD instead of using 2WD only.”

Using the grip offered by the transmission, this tip will see you increase grip levels and lessen the wear and tear on tyres.

“On the dirt it’s all about control, so with all four wheels hooked up via the transmission you’ll double the grip, making yourself doubly safe,” David says.

toyo d-max air pressure management off road driving

“I often see vehicles with their back tyres worn out well before time. The reason may not be obvious, but the wear is from wheel spin.

“In 2WD on corrugations the tyre will be spending a lot of time spinning. Using high range 4WD prevents this.

“That one could save you hundreds of dollars in unnecessary tyre wear.”

 off road driving toyo tires open country tyre pressure management

Inevitably, you will return to sealed roads. When you do, bring the tyres back up to the recommended pressure and revert back to 2WD.

Reinflating tyres when you return to a sealed road will reduce wear and prevent heat build-up and rolling resistance.

off road driving toyo tires open country tyre pressure management

For a quick and easy tip that was developed and is used daily by professionals, try the 20 per cent rule on your next off-road adventure.