Following Lance Stroll and Max Verstappen’s tyre failures at the Azerbaijan GP Pirelli had blamed it on some debris, an hypothesis that didn’t appear quite too convincing from the beginning.
“At the beginning the idea was that there was some debris cutting the construction because obviously the evidence of other tyres had some cuts on the tread. But then when we finalised investigation, we found that it was not due to the cuts,” said Isola.
“The cuts were due to debris, for sure, but the debris was not sharp enough to cut the construction.”
How did thing go in Baku then?
Teams are given prescriptions for minimum pressure. Prescriptions that are based on simulations with expected loads, downforce or speed.
"We assume that running at a certain pressure, a certain camber, with a margin, of course, we run in a condition that is okay for the tyre.”
"In that case, we didn't achieve these conditions, not because teams were doing something against the regulations, but because they were looking, as usual, for performance and that created a different scenario compared to what we were expecting,” he clarified.
And it’s in order to improve performances that teams run the tyres "at a lower pressure compared to the expectation.”
According to Mario Isola there was a difference of more than one Psi between the running pressures of the teams.
But “it was not just the lower pressure, there were also some other elements in the equation, that created the failure.”
What happened in Baku is that “the running conditions expected were different compared to the actual running conditions.”
“The failure was a circumferential cut on the inside shoulder – for both the tyres it was the same failure mode. When you have a lot of energy going into the tyres with a pressure that is lower compared to the expectation, the result is that on the sidewall you have what we call standing waves.”
“Standing waves are putting a lot of energy into the inside shoulder of the tyre. And, at a certain point, the tyre breaks. That is what happened, and the reason why we had this situation in Baku.”
In Baku only, as he shut down any speculations on whether it was the first time that teams messed with pressure parameters.
“We check every time the running parameters when we receive the telemetry data from the race,” he explained.
“We check everything on all the teams, of course, and also because it's an indication for the following race and its prescription, so we use the data.”