Pirelli’s tungsten tips are key to success in Sweden

Tungsten is best known as the key ingredient to the filament in electric lightbulbs but it also played a key part in Ford driver Mikko Hirvonen’s victory on Rally Sweden, round one of the World Rally Championship. Italian tyre firm Pirelli has a three-year deal to supply the series with tyres, running from 2008 to 2010.

In order to generate grip on a surface that is almost impossible to stand on, the rally cars run on Pirelli Sottozero snow tyres equipped with nearly 400 tungsten-tipped studs, which are designed to bite through snow and ice into the firmer surface underneath.

As suits the extreme environment of the World Rally Championship, tungsten is one of the toughest metals known to mankind. It’s got the highest melting point of any element other than carbon (around 3422 degrees Centigrade) and a very high density: about 19 times heavier than water.

This makes it ideally suited to propel rally cars through narrow and twisty snow-covered stages at average speeds that border on 120 kph. An even bigger challenge occurs when the cars pass through the stages a second time as the roads are often swept clean of snow, exposing loose gravel underneath.

Then the studs have to resist direct contact with the ground, which can rip them out completely. Pirelli benefits from a patented process in which the studs are inserted into the tyre at the time that the tyres are actually made, ensuring that most of them remain in place however challenging the conditions.

Although Swedish roads are so slippery that approximately 90 per cent of all new cars sold there come with some form of electronic stability programme, the Pirelli-equipped rally cars still manage to accelerate from 0-100 kph in less than four seconds and brake to zero again in even less time.

This attention to detail and high performance is equally evident in Pirelli’s road tyres, on which the competition tyres are based. The rally tyres also covered 1534 kilometres of road section throughout the three-day event, impressing Formula One driver Kimi Raikkonen, who is using Pirelli rubber on his first season in the World Rally Championship with the Citroen Junior Team.

Hirvonen’s victory meant that his season got off to the best possible start, after the Finn suffered the heartbreak of losing out on the drivers’ title by just one point last year. "The tyres were excellent," said the Ford driver, who eventually won by 42.3 seconds from Citroen’s six-time world rally champion Sebastien Loeb. "Even when the stages were cutting up, we still enjoyed a good level of grip, which allowed us to take our first win on Rally Sweden."

Pirelli’s motorsport director Paul Hembery concluded: "Although our competition tyres use cutting-edge technology such as tungsten tips, most people do not realise just how closely related they are to our road tyres. World Rally Championship rules mean that our rally tyres are the same size as our road tyres and all the lessons we learn about traction and grip from snowy rallies are put directly to use in the tyres we make for the road. On behalf of everyone at Pirelli I’d like to congratulate Mikko on a fantastic victory, at the start of what is set to be a tremendously exciting World Rally Championship season."