Pirelli can’t explain why its C6 tyre was so bad in Imola GP qualifying

Pirelli’s new C6 tyre made its maiden appearance as part of the race-weekend at Imola but left everyone, including the tyre supplier itself, baffled when competitors struggled to make it last over a single lap. The two Aston Martin drivers and Mercedes’ George Russell set their best laps in qualifying on the C5, which is the medium tyre selection for the Imola GP.

What’s all the more surprising is that after Friday’s two practice sessions, the first meaningful test of the new soft compound, most of the comments were positive.

Pirelli claimed it offered a noticeable step up in grip from the C5 and the difference in laptime between the two was even greater than its simulations had suggested – up to half a second a lap rather than 0.2-0.3s.

But this positivity evaporated on Saturday as every team found the C6’s performance dropped off dramatically over the course of a push lap unless it was managed perfectly.

This was what pushed Mercedes to send Russell out on the C5 for his final Q3 run, compromising his available tyre selection for the race. It emerged that Aston Martin had already taken the decision to use both the C5 and C6 in qualifying on Friday night.

Speaking after qualifying but before all the data had been analysed, Pirelli motorsport manager Mario Isola admitted that the reasons for the C6 not working as expected were not yet clear.

“I believe, and the general comments from drivers is that today [Saturday], they experienced more understeer compared with yesterday, and this could explain the reason the track was not quicker,” he said.

“If you look at the lap times, not much quicker than yesterday. We had very little track evolution, and together with the understeer they said it was difficult to extract the performance from the C6.

“So, the C6 was more difficult to use, probably the preparation lap was difficult. We cannot find a clear trend in the sector times to say that there was a degradation from sector one to sector three.”

Although the expectation was that the C6 would be up to half a second quicker per lap, when pushed on Saturday it proved to be less predictable and consistent than the C5 – which accounts for why many drivers who tried the medium in FP3 and qualifying were able to go faster than they were on the soft.

Several teams also observed that their drivers were able to extract a better lap time from a C6 that had already been used.

Pirelli’s explanation for this was that the used tyre’s performance peak was lower, but more predictable and easier to access.

“If we consider that this compound is very soft and, as usual with a soft compound, you have a curve of grip with a peak that is a bit more sharp,” said Isola.

“Then obviously if you give a heat cycle to the new tyre, you have a slightly different curve of grip with less peak, and that means it is a bit easier to use a tyre like this.”

Less easily explained was the shift towards understeer. Pirelli had dropped the minimum pressure for the rear tyres by one psi overnight but this in itself would not be likely to account for such a change in balance.

Often teams dial in understeer to protect the rear tyres – but if it was a deliberate setup choice it seems counter-intuitive to complain about it.

“It is not clear why they were complaining about this additional understeer compared with yesterday because there are no elements to support this,” said Isola.

“We didn’t have any rain overnight or anything strange, but the track seemed to be slower compared with yesterday – and everyone, in general as an average, we had this comment of additional understeer compared with yesterday.

“Yesterday the limitation was the rear, today it seems that was more the front.”

What makes the change even more puzzling is that the weather conditions were largely consistent from day to day, though the wind had changed direction.

The use of different engine power modes for qualifying is also unlikely to account for the shift, since the C6 was also problematic in Saturday’s third practice session.

“We know that one psi in both directions, if you increase or you go down, is not really changing the balance,” said Isola.

“It never happened before so I cannot imagine that. There is something bigger that we haven’t discovered yet that was going to change this balance.”

Further analysis will indicate whether teams’ setup choices did have an influence. The length of Imola’s pitlane naturally steers teams towards a one-stop strategy because the time loss is in the order of 28 seconds.

Protecting the tyres as much as possible therefore becomes imperative – so it’s possible that, having observed the rear axle to be a ‘limitation’, teams deliberately dialled in more understeer to protect the rear tyres. It’s common practice but, working with an unfamiliar tyre compound, they may have got more understeer than they expected.

Despite this weekend’s stumble, Pirelli intends to push on with its plan to roll out the C6 at more races and potentially ‘skip’ compounds in its tyre selection – essentially building in a disincentive to run one-stop strategies.

Since the entire tyre family is homologated for the year and cannot be changed, that is the only option on the table: find a solution using the tyres that already exist.

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