Ski runs are classified according to their level of difficulty with green runs set aside for beginners and black courses for the exclusive use of expert skiers. Borovets, Bulgaria’s oldest ski resort, has 19 ski runs including the black-graded Yastrebets descent, which measures 2300 meters in length and is arguably the town’s toughest course for those hoping to emulate Carlo Janka, the current overall skiing World Cup champion.

Borovets is also home to another tough course, the 220.03 miles of Rally Bulgaria, round seven of the 2010 World Rally Championship, of which Pirelli is the exclusive tire supplier under a three-year agreement with the FIA, motorsport’s world governing body.

Although Borovets is located high up in the Rila mountains, being early July, it’s not surprising to learn that the rally used Tarmac-only runs rather than snow-coated grassy slopes. However, its lofty location means the weather can be unpredictable. During the four-day event, crews experienced bright sunshine, heavy clouds and rain, while ambient temperature variations ranged from 46 degrees Fahrenheit to 85+ degrees Fahrenheit at the rally’s permanent service park in Dolna Banya.

It was the threat of unpredictable weather that made the availability of the soft compound Pirelli P Zero tire essential for the competing crews. On gravel events, WRC regulations restrict drivers to a pre-determined compound of Pirelli’s Scorpion tire. On asphalt events, they can choose between the hard (for dry conditions) or soft (for wet conditions) compound P Zero, albeit with a restriction of 40 covers in total. In Bulgaria, they had an allocation of 34 hard compound tires and 24 soft compound tires, eight more than usual, following reports of possible thunderstorms.

While the event was held in largely dry conditions, overnight showers and precipitation on Saturday morning’s opening brace of stages forced competitors to choose between the hard and soft compound tire and dramatically increased the challenge due to the inconsistent stage surfaces.

Both types of compound use an identical tread pattern, designed to provide maximum contact with the road, but the soft version is designed to provide more grip and stability when conditions are cold and damp, while the hard provides optimum performance when the weather is warm and the road surface dry.

Sebastien Loeb, who won the rally to extend his lead of the world championship to 51 points, opted for the soft compound P Zero tire for all of Saturday’s six stages to counter the threat of showers. While it proved a wise move by the factory Citroen C4 driver on Saturday morning, it was less inspired in the afternoon when it remained dry.

“We expected some rain so it was a safety decision because when you have water on the road the soft compound tire is much better,” said Loeb. “If it’s dry we knew it would not be the best choice but we did not lose too much time because the grip under braking was still good when we used the soft compound tire on a dry surface, although we could not be so quick through the corners because we have less lateral grip and you have to find a different rhythm for that.”

Loeb’s victory was his 58th at world championship level, the 22nd time he had triumphed in the WRC using Pirelli tires and his seventh win on asphalt with Pirelli covers.

In the past, Pirelli engineers would have developed a tire specifically for competition and for different levels of rainfall. But because the FIA specified that the asphalt tires had to conform to everyday road use regulations, the P Zero WRC cover is virtually identical to the tires available for members of the public, albeit with even stronger sidewalls to combat the threat of punctures. Nevertheless, Loeb was quick to praise the performance of his Pirelli P Zero tires.

“It’s been the perfect rally for me and very good for the championship,” said Loeb. “I am happy with the performance of the tires and I was surprised that the soft was as good as it was in dry conditions when, for sure, it was not the best choice.”

Rally Bulgaria also marked the debut of Pirelli’s new RX tire for use by Junior World Rally Championship competitors in place of the old RS design. Using the same technology incorporated into the 18-inch RX tire, Pirelli has produced 17- and 16-inch versions to give the competitors in the young-driver class more precision, reaction, durability and consistency, particularly on some of the longer stages (the Batak Lake stage run twice on day one measured 19.74 miles in length) on the rally route.

Thierry Neuville, who claimed his maiden win in the JWRC class in a Citroen C2 S1600, said: “The tire was working very well. (We) had a very good feeling and there is not much difference between how the tire looked at the start and finish of the long stages. It’s very good work by Pirelli.”

“We are very satisfied with how this rally has gone for us,” Matteo Braga, Pirelli’s senior WRC tire engineer, concluded. “It is a new rally and the first round of the WRC on Tarmac this season so there was increased expectation. The teams are now clear about how the soft and hard tires perform in different conditions and this is very important. Also, Petter Solberg used the same set of tires on Friday’s stages, which covered (74.56 miles), and this shows the durability of the tire is very good. We’ve seen no tire damage or punctures although there were some junior drivers who had problems by cutting corners and hitting rocks, which broke rims rather than the tire.”

The World Rally Championship resumes in Finland from July 29-31.