Silverstone tyre failures a result of high kerbs and unconventional usage – Pirelli

Pirelli has released two statements to explain the reasons behind the spate of tyre failures at the British grand prix. The exclusive tyre supplier said that the “sophisticated” asymmetric construction of the current P Zero Formula One slicks meant that tyre management methods employed by teams, such as mounting rear tyres on the opposite side to that for which they were designed, reduced tyre pressures, and extreme cambers had combined with the high kerbs at Silverstone to cause the problems, which Pirelli Motorsport director Paul Hembery described as “completely unexpected”. While Hembery was adamant that the “2013 range of tyres, used in the correct way, is completely safe”, he accepted that Pirelli had “underestimated” the effects that these unconventional running techniques would have on the tyres, and had declined to forbid mounting tyres the wrong way around. In future, Pirelli is seeking, with the agreement of FIA, FOM, the teams and the drivers, greater control over the ways in which its F1 tyres are utilised.

Pirelli’s “exhaustive analysis of the tyres used at Silverstone” led to its following conclusions as to the major contributing factors to their failure:

1) Rear tyres were mounted the wrong way round: Pirelli found that the right hand tyre was placed where the left hand tyre should be and vice versa on the cars that suffered failures. Pirelli explains that this is problematic because the 2013 tyres have “an asymmetric structure… not designed to be interchangeable.” Their sidewalls are designed to deal with “specific loads on the internal and external sides of the tyre”, meaning that swapping tyres affects how they work in certain conditions. The external side of the tyres is designed to cope with the very high loads generated under cornering at demanding circuits like Silverstone, which has “rapid left-hand bends and some kerbs that are particularly aggressive.” Pirelli said that the dangers of this practice were “underestimated by everybody; above all Pirelli, which did not forbid this.”

2) Excessively low tyre pressures: Teams set the pressures of their tyres below the nominal level set by Pirelli, which currently has no control over teams’ strategic decisions in this respect. This meant that the tyre was able to flex and bend out of shape more, increasing its working stress. 

3) The use of extreme camber angles: Pirelli also has no control over the camber – or the angle at which the wheel is positioned in relation to the track surface – settings employed by teams. As with tyre pressures, they are currently free to make strategic decisions on this factor depending on the interaction of their cars with the rubber. The tyre supplier has asked the FIA to make these parameters a topic for accurate examination in future, with checks conducted “by a dedicated delegate”.

4) Aggressive kerbing on fast corners: immediately after the grand prix, commentators and analysts identified the sharp lip at turn four, around which some failures occurred. Pirelli says that this was the reason for the left-rear tyres being affected.

Pirelli also stood by its assertion that the laboratory-developed bonding process introduced before the British grand prix to eliminate the delamination issues experienced earlier in the season was not a cause of the failures. The new bonding method was Pirelli’s reaction to some teams’ rejection of its previously suggested method for resolving this issue – a new Kevlar-belt tyre. When it rained during practice for the Canadian grand prix, teams were not given adequate time with the proposed new tyres, which were to be supplied at Silverstone. Thus the new bonding solution was employed instead.

Regulation of tyre use ‘essential’

Pirelli’s conclusion after this analysis is that “it is essential for tyres with the performance and technical sophistication of the 2013 range to be regulated and carefully controlled by Pirelli itself”. The company is requesting “real-time data from the teams regarding fundamental parameters such as pressure, temperature and camber angles”. Since new regulations are subject to approval from many different interests, it is wise of Pirelli to have a more short-term measure in place, and the tyre supplier has agreed a number of measures for forthcoming grands prix with the FIA, FOM, the teams and the drivers.

Firstly it confirmed what had already been widely discussed as an immediate option for the German grand prix, starting with Friday practice on 5 July; the use of an “evolution” of the 2013 tyre minimally, but reliably, tested in Canada. Pirelli says the tyre “represents the best match for the technical characteristics of the Nürburgring”. It has a Kevlar construction that replaces the current steel structure and the re-introduction of the 2012 belt, to increase stability and road-holding. The tyres remain asymmetrically structured, so a measure has been agreed to forbid fitting them to the opposite axle. This only goes for the rear tyres, since the front tyres will remain in the original 2013 specification.

From the Hungarian grand prix, Pirelli will introduce a new symmetrically structured range of tyres, which will help the manufacturer to guarantee their safety without access to tyre data. These are by design less sophisticated products, since Pirelli has confirmed that the optimal function of the more sophisticated 2013 tyres depends on its regulation of their use. Pirelli said the new tyres would combine the characteristics of the 2012 tyres with the 2013 compounds, which were brought in to reduce lap times and give teams wider working ranges. Before Hungary, the 2012 structure, 2013 compound hybrid will be tested at Silverstone with the teams and their 2013 cars at Silverstone from 17-19 July during the young driver test. Teams will also be given the opportunity to carry out the appropriate set-up work on their cars.

Paul Hembery concluded: “What happened at Silverstone was completely unexpected and it was the first time that anything like this has ever occurred in more than a century of Pirelli in motorsport. These incidents, which have upset us greatly, have stressed the urgency of the changes that we already suggested – which will be introduced during for free practice in Germany on Friday. 

“We would like to acknowledge the willingness of the FIA, FOM teams, and drivers to act quickly to find an immediate solution to the problem. In particular, the adoption of winter tests, arranged with the FIA, that are more suitable for tyre development and the possibility of carrying out in-season testing will contribute to the realisation of tyres with increasingly improved standards of safety and performance.”

Hembery said that Pirelli’s investigation had also concluded that “the 2013 tyre range does not compromise driver safety in any way if used in the correct manner, and that it meets all the safety standards requested by the FIA.” 

Hembery also released a follow up statement to clarify the tyre supplier’s stance, which he said was not intended “to create arguments or to attack anybody”, and was given the “collaboration and support” of “teams, drivers, FIA and FOM”. He continued: “We have taken our responsibilities upon ourselves as our press release indicates. But not having full control over all the elements that impact on the use of the tyres, we need everybody’s contribution. With regard to this, we are receiving the full support of all the parties involved, for which we are very grateful.”

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