Sebastian Vettel's tire blows in the closing stages of the 2015 Belgian Grand Prix costing him a podium finish.
Pirelli has released the findings of its investigation into the Spa tire failures – and the Italian company is adamant that its products were not at fault.
Instead it says that the problems faced by Sebastian Vettel and Nico Rosberg were down to external factors, or in other words debris.
At the same time, Pirelli has not entirely backed down on Ferrari’s usage issue by stressing that Vettel’s long second stint at Spa left the tires worn and more susceptible to damage from debris.
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Pirelli’s conclusions were as follows:
“The tests carried out by Pirelli on the tires used at Spa have confirmed the absence of any structural problems. Pirelli has undertaken in-depth analysis on the materials and production processes used, utilizing two different methods of tests and checks.
“Microscopic analysis, carried out on a large number of the tires after the second free practice session, showed no signs of fatigue or integrity issues. The same result was confirmed for the tires used during the race, which were cross-sectioned and analyzed in Milan. Some of the tires used in the race were subjected to a further laboratory fatigue test, passing all the assessments conclusively and confirming that there was no structural degradation or problem on-track.
“Since the start of 2015, 13,748 slick tires have been used: including on especially severe tracks like Sepang, Barcelona and Silverstone. No problems have ever been discovered, underlining the fundamental solidity of the product.”
In the second part of its conclusion, Pirelli underlined that external factors had caused the cuts in Belgium, while stressing that worn tires were more vulnerable.
“The events of Spa can therefore be put down to external factors, linked with the prolonged use of the tires on one of the most severe tracks of the championship.
“The external factors are demonstrated by a total of 63 cuts found in the tread of the Formula One tires used over the course of the Spa weekend, following numerous incidents that took place during the support races before the Formula One Grand Prix. In the previous 15 events (10 races and five test sessions) an average of only 1.2 cuts per event were noted. All this indicates an anomalous amount of detritus on the track in Spa, with a consequent increased risk of encountering a foreign object.
“If even a small piece of debris – made of carbon or any other particularly sharp material – penetrates and cuts the various structural parts of a tire (which is obviously subject to high-speed use, and more susceptible if used for a prolonged period) without penetrating the actual structure, this can cause a failure that is different to that found in the event of a normal puncture, which is characterized by a loss of tire pressure. And the former was the type of event seen on Sebastian Vettel’s tire at Spa.
“As for Nico Rosberg, in whose case the tire usage was less, the tire held up – as the footage clearly shows – and the failure was not instantaneous. For four corners previously, an element of the internal structure of the tire was visible, coming out of the tread pattern. This highlighted the existence of the damage and the consequent start of the tire’s attrition.
“Throughout the Spa weekend (including practice, qualifying and the race) cuts caused by debris were found on the tires of other drivers, which damaged the construction but did not cause any failures.”
Pirelli concluded by noting that it has talked to the FIA about the issue of debris.
“At the end of qualifying on Saturday at Spa, following the exceptional number of cuts noted to the tires, Pirelli pointed out the condition of the circuit to the FIA and asked for it to be cleaned, as well as for the teams to be told. The FIA reacted promptly in arranging for the track to be cleaned and advising the teams.
“Together with the FIA, Pirelli proposes a study to evaluate the way in which circuits can be cleaned most effectively.”
Meanwhile, the FIA issued its own response to the Pirelli conclusions, noting “The FIA is willing to consider any safety recommendations made by the tire supplier for the Italian GP and the remainder of the season.” It also added that Pirelli has decreed that Vettel’s tires only had 30 percent of their tread left when he had the failure at Spa.