Pirelli has released its findings following an investigation into why Sebastian Vettel suffered a high-speed tyre failure towards the end of the Belgian Grand Prix, with the emphasis being placed on the Spa-Francorchamps circuit itself after higher than normal 'tread cuts' across the field.
Vettel and Ferrari launched a scathing critique of Pirelli in the wake of the Belgian Grand Prix after Vettel's right-rear tyre failed with just over a lap remaining. It came two days after Nico Rosberg also suffered a high-speed tyre failure himself, though Pirelli speculated that the former had pushed its stint too far, while debris was to blame for the latter.
Following a detailed analysis of the tyre, Pirelli has now concluded that a series of reasons were ultimately to blame for Vettel's failure, with the 'combined effect' of debris on the track and the prolonged tyre usage at fault. The FIA went on to add that the tread thickness on Vettel's rear tyres was approximately 30 per cent at the time of the failure, making it more susceptible to damage from the aforementioned debris.
With Pirelli ruling out any structural problem with the tyre itself, of particular note is the discovery of 63 cuts in tyres over the course of the weekend. Pirelli says it experiences on average just 1.2 cuts per race (including tests), suggesting debris on a particularly 'demanding circuit' was having a potentially damning effect.
As a result, Pirelli has recommended the FIA 'undertakes a study to optimise the way in which circuits are cleaned'.
Read below for Pirelli full and detailed analysis:
The tests carried out by Pirelli on the tyres used at Spa have confirmed the absence of any structural problems. Pirelli has undertaken in-depth analysis on the materials and production processes used, utilising two different methods of tests and checks.
Microscopic analysis, carried out on a large number of the tyres after the second free practice session, showed no signs of fatigue or integrity issues. The same result was confirmed for the tyres used during the race, which were cross-sectioned and analysed in Milan. Some of the tyres 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 tyres 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.
The events of Spa can therefore be put down to external factors, linked with the prolonged use of the tyres 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 tyres 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 tyre (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 characterised by a loss of tyre pressure. And the former was the type of event seen on Sebastian Vettel's tyre at Spa.
As for Nico Rosberg, in whose case the tyre usage was less, the tyre 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 tyre was visible, coming out of the tread pattern. This highlighted the existence of the damage and the consequent start of the tyre's attrition.
Throughout the Spa weekend (including practice, qualifying and the race) cuts caused by debris were found on the tyres of other drivers, which damaged the construction but did not cause any failures.
At the end of qualifying on Saturday at Spa, following the exceptional number of cuts noted to the tyres, 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.