Pirelli believes debris led to the spectacular tire failures for Max Verstappen and Lance Stroll in the Azerbaijan Grand Prix, after also finding a cut on the same corner for Lewis Hamilton.

Stroll suffered a left-rear failure on the run to the finish line on Lap 30 — having yet to pit after starting on hard tires — but very few teams made a precautionary pit stop as they felt the issue was not due to tire wear. However, when Verstappen then crashed in the closing stages at the end of the same straight, the race was red-flagged to allow teams to change tires. Despite that, Pirelli motorsport boss Mario Isola believes the issues were both caused by debris and says a cut for Hamilton supports that theory.

“Obviously we didn’t have the time to perform a full investigation and we need to send the tires back to Milan,” Isola said. “The plan is to send both sets to Milan by air freight tomorrow in order to have them in our laboratories as soon as possible and be able to make an investigation on these sets, plus some other sets used in the same stints. Because looking at the tires used in the second stint, for most of the drivers we didn’t find anything.

“I believe I can exclude that the failures were due to tire wear, because it’s not a matter of tire wear. We found a cut on the inside shoulder of a rear left tire used by Lewis Hamilton in the same stint. The cut was quite big and deep — probably 6-7cm (2.3-2.8 inches) — but not cutting the construction, so the tire is in one piece, just the tread is cut.

“When there was the red flag and Lewis came to the pit lane and changed the set of tires, we were able to find the cut in the tire. The rear left tire is not the most stressed tire, in Baku, because talking about the rear tires, it’s obviously the rear right.

“This is the preliminary investigation. Another element is that there was no sign or warning according to the teams. We have to receive the telemetry from them but what they told me is there was no warning, no vibration, nothing to think there could be something (wrong) with the tires.

“These are the main elements collected in the short period of time, considering that the tires fitted on the cars that crashed got back to the garage and our fitting area just a few minutes’ ago, so we need a bit of time to analyze them.

“I don’t want to give any preliminary conclusions, but it seems that it is a cut due to debris. As I said it’s not the most stressed tire, we have evidence of another cut in the same position, both the accidents happened on more or less the same part of circuit with a few laps difference. We had a number of other cars with the same laps on their tires without any issues, so preliminary investigation is it is probably due to an external factor — debris, a curb or whatever.”

While Hamilton didn’t suffer a failure, Isola says his issue was clearly caused by something external damaging the tire.

“The cut on Lewis’ tire is clearly coming from debris. It is clear because the tire is still in one piece and you can see that the cut is not in any direction, it’s a cut that is … clearly coming from outside.”