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Workshop: Tyre Tech


Words Martin Pretorius

The ageing ML500 almost didn’t make it to the family’s picnic spot, falling foul of a muddy incline about halfway up the access path. Recent rain and poor drainage had turned the fairly good dirt road into a slushy mess, in which neither German engineering nor fancy electronics could
create motion without friction, and all its power went to waste in a spray of mud and lots of old-school V8 exhaust roar.

Fortunately, a hero with a Hilux came around with a tow rope and swiftly pulled the mud-splattered SUV to level ground, proving that it’s unwise to under-estimate the importance of the right equipment.

It all begins with the tyres. While nobody in their right mind would take a softroader to a 4×4 jamboree, except as a towing vehicle, the main reason for its compromised performance in mild off-roading is based not only on its lack of ground clearance or the (usual) absence of a dedicated low-range transmission.

Air suspension can lift the vehicle’s belly, gearboxes with up to nine speeds usually feature crawler gearing in their lower ranges, and stability control can emulate locking differentials remarkably well.

The level of technology in modern vehicles does a very good job of simulating proper off-road hardware. But all that means nothing if it’s running on inappropriate tyres. Even if the hardware is capable of sending power to the appropriate wheels, it will all come to naught if that power can’t be transferred to the ground. This applies to serious off-road machines and pavement-pounders alike.

Our friend with the Mercedes ML was probably mortified when that Hilux dragged him out of the quagmire, but good off-road ability is probably the
furthest thing from his mind on the school run.

You won’t find off-road tyres fitted as standard equipment on road-biased vehicles, because their typical buyers aren’t really dreaming of venturing onto anything more strenuous than the odd dirt track. Softroaders are primarily designed to be quiet and comfortable on the tarmac, stable around
corners, and economical to operate: objectives most easily met by fitting lower profile tyres with more car-like tread patterns and compounds.