GP2 qualifying red flagged to inspect the kerbs.

Pirelli has revealed that '90 percent' of the tyres run in the closing minutes of first free practice were cut by the loose kerb retaining bolts.

The tyre supplier discovered the cuts at the end of the session and immediately informed F1 race director Charlie Whiting that there was potentially something wrong with the circuit.

That information prompted Whiting to immediately red flag GP2 qualifying so he could inspect the kerbs, which uncovered the problems with the loose bolts at Turns 6 and 12.

Pirelli racing manager Mario Isola said that the problem was not isolated to just a few cars, as almost all those running at the time were affected.

"I can say 90 percent of the tyres had a cut so it was a good indication that something had to be investigated," explained Isola.

"They [the FIA] investigated the kerbs after our information that we found, on most of the tyres used in the last part of FP1, some cuts on the rear left tyres.

"All the cuts were in a certain position so they were more or less the same – and we informed Charlie Whiting and he reacted immediately. He went out just before the qualifying session of GP2 and was checking all the kerbs on the left side of the cars, and he found a couple where some small bolts came out.

"They fixed it – but they just had to postpone the GP2 qualifying session. They fix it and they will work tonight to have a final solution on that.

"For FP2, we checked the tyres used in FP2 and we couldn't find anything, so everything is okay now."

Deep Cut

Isola clarified that the cuts – some of which were 5cm long – had not gone through the entire tyre, which is why there was no loss of air from any of those affected.

"They were quite deep on the tread, touching the construction, but we didn't have any tyre failures or any air loss. Obviously it is something we had to fix. But nothing happened."

Not debris

Isola also said that the idea that the cut was being caused by something permanent was prompted by the fact that the issues were happening at the same location on each tyre.

"On all of them you can see an external object cutting, so there was an indication, a direction of the cut. So it was quite clear that it was something, not only a piece of debris.

"If you have a piece of debris, you can have a cut in different positions because the debris is moving, it is not fixed - while the position and the shape of the cuts were indicating something probably on the track. We gave all this information and that is why they investigated."

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Gallery: Pirelli says 90 percent of tyres were cut by kerb bolts