The ordeal of an off-road tyre

Wednesday, 28 December 2011

backtonews

Off-road tyres must be capable of delivering consistent, top performance over hundreds of competition kilometres at a time, in all types of conditions: from searing heat, dust, rocky terrain, jumps and sand to mud and torrential rain.

The punishment faced by off-road tyres comes from two sources: the terrain and the demands made of them by the vehicles themselves.

More than anything else, they need to be robust and versatile enough to be competitive across the full spectrum of conditions encountered in the course of the rally, and even during a single day's action. The challenge ranges from rough and/or rocky tracks to sand, dust and fesh-fesh. Factory drivers and drivers with factory backing may only use one type of tyre for the entire event.

To adapt their tyres to the conditions of the moment, the only thing crews can do is adjust their tyre pressures. Stony terrain calls for relatively high pressures (around three bar) in order to protect them from the incessant knocks. It is not rare for a rim to shatter before a tyre shows any sign of damage! In contrast, lower pressures (approximately 1.4 bar) are preferable when it comes to crossing sand dunes, since low pressures ensure a bigger contact patch.

Meanwhile, tyres must be capable of withstanding the physical constraints imposed on them by the factory prototypes such as the MINI ALL4 Racing, which delivers more than 300 horsepower for a weight of approximately 2.5 tonnes at the start of stages (with a full tank and two spare wheels), while its top speed is close to 200kph. When landing on one wheel after certain jumps, for example, a single BFGoodrich All-Terrain+ tyre may have to soak up a dynamic load of up to 3.5 tonnes, which is 150 times its own weight!