BARCELONA May 11 Pirelli are reviewing the construction of their Formula One tyres after a series of spectacular debris-related failures but have assured drivers they need not worry about safety.
Concern was expressed at the Spanish Grand Prix when the tread came off the still-inflated left rear tyre of Paul Di Resta's Force India during Friday's second practice.
Ferrari's Felipe Massa suffered two failures during the Bahrain Grand Prix last month and Lewis Hamilton collected a grid penalty after his Mercedes needed an unscheduled gearbox change following tyre damage.
Paul Hembery, Pirelli's motorsport director, told Reuters on Saturday that the problem occurred when debris on the track penetrated the tread rather than the sidewall of the tyre.
This was because the Italian manufacturer has introduced a high-tensile steel belt under the tread to make it hard for objects to penetrate the tyre and cause a sudden deflation.
"What we have changed this year...is that when there is debris or an issue, it doesn't cut through the belt pack and deflate the tyre which is what would have happened last year," he said.
"Instead, it's arriving at the belt pack and then you get the tread being the weak point. It overheats and comes away, which visually is very dramatic although the structure is still intact."
Hembery said Di Resta's tyre still had a pressure reading of 17 psi when the car came back to the garage.
"Last year that would have collapsed on to the rim and (the car) probably would have crawled down the pitlane on three wheels. It's the mode of failure that's changed," explained the Briton.
"Bizarrely, it's probably safer this way.
"For us, it's worse because it's visually - from a tyremaker's point of view - not great. From a safety point of view, it's probably safer because the actual tyre is still inflated. It's not something due to quality or design."
Hembery said Pirelli would seek a solution to the problem but it would not be available until at least the British Grand Prix at the end of June because teams would have to agree any changes that could affect performance of their cars.
That will mean similar failures could occur at the Monaco and Canadian Grands Prix before Silverstone.
"We can't test and if we make too dramatic changes we influence maybe the aerodynamics and some of the chassis design," said Hembery.
"If we make anything significant, we have to convey it to the teams and we have to know if that is going to affect what they are doing. It's a very delicate balance.
"Is our solution to make the tyre deflate when it has debris? Does that look better from a tyre maker's point of view? Is it worse for the teams or better? It's a strange dilemma to be in," he added.
Hembery said Hamilton's issue in Bahrain was slightly different to others, in that there was either a suspension problem or something on the track that broke the suspension, but Massa's punctures were clearly caused by debris.
"There were cuts in the tyres. I found a bit of one car in one (tyre) and I know which one it was because it had the branding on it," he said with a smile.
"We are frustrated, because we don't like to see it (the tread coming off) but we are not alarmed for any safety issues." (Editing by Ed Osmond)