What tyre pressure should I use for off road driving?

We received an e-mail from Ken, a 2014 Jeep Grand Cherokee owner, who wanted to know what wheels and tyres he should use for off-road driving.

Q: I purchased a 2014 Jeep Grand Cherokee Limited in November 2013. I have driven (and towed a caravan) for 30,000km and have enjoyed the driving experience. My concern relates to the wheels/tyres. On Bruny Island, Tasmania last year I received a ‘nick’ in the wall of a front tyre and had to replace it. What occurred to me then was the tyre profile- 265/50 on a 20inch wheel. I think this is the same on the Overlander.

The Grand Cherokee Laredo has an 18-inch wheel with a higher profile tyre. After my experience on Bruny Island I am hesitant about driving off-road with such low profile tyres. I read your review of the Overlander and would like your views on the wheel/tyre size for off-road driving. I am aware that the Overlander has a height adjustment but that would not affect tyre size.

A: When it comes to driving off-road, tyre pressures are critical to tyre longevity.

With a low-profile tyre, it’s important to make sure your tyre pressures are set correctly. The reason pressures are so important is that if you hit a sharp object (such as a rock), a lower pressure tyre can effectively mould around the rock instead of penetrating the rubber.

Low-profile tyres exacerbate this issue further as the distance between the tyre contact patch and the alloy is smaller. An impact at speed will likely cause the tyre to be penetrated.

For off-road driving, it’s highly recommended to choose a higher profile tyre (your Jeep is a 50 profile, while the entry level Laredo is 60) and to set recommended pressures.

The height adjustable suspension will aid in ground clearance and driving over high objects, but won’t help prevent tyre damage.

If a new set of wheels with a higher profile tyre is out of the question, your best bet is to drive slow over rocky terrain and set correct tyre pressures before setting off (remembering to reset them when you hit the black-top again).

Each type of off-road driving requires different tyre pressures. For sand driving, by decreasing tyre pressure, you inevitably increase the contact patch of the rubber on the sand, which gives the tyres a greater chance to dig in.

As a rule of thumb, 18-22psi is appropriate for sand driving, which is around half the normal operating pressure for a tyre. You should set this pressure just before you drive on the sand and also ensure you have a motorised pump to fill the tyre back up when you drive back onto the black top.