EVEN though the minimum legal tread depth is 1.5mm, grip reduces when tyres get down to 3mm. You’re more likely to get a puncture when this happens, especially when off-road.
If you’re about to go on a big trip, then a fresh set of tyres is ultimately a cheap form of insurance – even though most 4x4 tyres aren’t exactly cheap. You’ll have the better tyre grip and a much better chance of avoiding punctures.
Most tyre manufacturers recommend that any tyre more than six years old should be replaced, irrespective of how much tread it has. So that never-used spare sitting on the back of your 4WD for the past 10 years isn’t going to be much use. Rubber degrades (as does the tyre’s steel reinforcement), especially when out in the elements, so the risk of a blow-out is very high after about six years. Rubber hardens on old tyres, too, which you will find out the hard way the next time you drive in the rain.
Most tyres have a four-digit production date stamp on the sidewall. The first two digits represent the week of the year they were produced and the last two digits represent the calendar year. So the figure ‘4210’ on a tyre means that it was made in the 42nd week of 2010. If the sidewalls or tread area has small cracks showing, then the tyres should be thrown away.