Arctic Rally 2021: how competition tyres improve grip on snow and ice

Typically, the chance to see the World Rally Championship compete in full snow and ice conditions only comes around once a year – but watching the cars travelling flat-out through such wintery surroundings is one of the most impressive and spectacular sights of any season. And it's all made possible thanks to some very special tyres.

The WRC's annual snow date on Rally Sweden has one of the highest average speeds of the year – and its replacement for the 2021 season, Arctic Rally Finland, could be even faster. And colder. That is despite the fact that it would be difficult to walk on such slippery surfaces without falling over.

Key to the spectacle is the use of studded tyres made specially for rallying on snow and ice, which bite into the surface to provide incredible levels of grip. For its return to the top level of the WRC in 2021, Pirelli has developed the Sottozero Ice J1 tyre, featuring close to 400 studs – each one protruding a maximum of seven millimetres out from the tread.

When the stages have a smooth and thick layer of ice, those seven millimetres give the drivers superior grip to what they can experience on gravel or even on asphalt, helping them to achieve speeds of up to 200kph.

In the WRC, only a single type of tyre is permitted on pure winter rallies like Sweden or the Arctic. That means the drivers don't have difficult decisions to make during the event about which rubber to use, like they do on Rallye Monte-Carlo, where the Sottozero with short studs is also an important option.

But it also means the specialised tyre for Finland with its seven-millimetre studs must be capable of performing in all of the possible conditions, and these are often far from consistent. For this reason, a good snow tyre is about more than just the studs.

If lots of fresh snow has fallen on the stages since they were prepared, it becomes harder for the studs to reach through to the ice and find purchase. For this reason, the tread pattern is designed to clear away loose snow.

The pattern is asymmetrical, so different tyres are made for the left and right-hand sides of the car. The inside half of the pattern features longitudinal tread blocks, which provide maximum traction when accelerating and grip under braking. The external tread has diagonal blocks to help when turning through a corner.

The tyres also have to deal with a lack of snow and ice – a scenario that has been increasingly common over recent years on Rally Sweden in particular. Milder temperatures can expose gravel underneath the snow or ice, which can damage or rip the studs from the tyre.

For this reason, the tips of the studs are made from tungsten, a metal known for being robust. Furthermore, to help prevent studs being lost, much of their total length is hidden out of sight within the tyre, and are locked into place during a Pirelli-patented process of vulcanisation.

All of this means drivers can push to their limits on snow and ice, knowing the metal in their tyres will give them a remarkable amount of grip on such slippery surfaces. The trick is to trust it, however unnatural it might seem. Most drivers say that the amount of grip available on snow and ice with studded tyres is similar – or slightly more – than you would find on gravel with gravel rally tyres. The main difference is the way in which the grip is delivered. A gravel tyre loses grip quite progressively as the car slides, whereas the studded tyre is more of an on-and-off switch: it either grips or it doesn't.

The problem seen before in Sweden of a lack of ice and snow won't be an issue in northern Finland; close to the traditional home of Santa Claus in Rovaniemi. In the past, temperatures have dipped down to colder than minus 30: one year an entire loop of stages was cancelled because it was too cold for the marshals to be stood outside. This time, the conditions shouldn't be that brutal, but there will still be enough ice and snow around to showcase the cars – and the unique tyres – at their very best. The feeling of driving the Arctic Rally is like no other: one reason why, as well as the off-road regulars, it's attracted Formula 1 drivers such as Valtteri Bottas and former world champions Mika Hakkinen and Keke Rosberg in the past. Watch it on wrc.com to find out why.