Mario Isola believes teams' qualifying strategies on Saturday will likely be determined by the level of degradation of Pirelli's hypersoft compound, a tyre many criticized after Friday's running.
The Italian manufacturer's softest rubber logically produced the fastest laps around the Autodromo Hermanos Rodriguez, but its durability was also called out by the drivers, making it perhaps an unpractical choice for qualifying, let alone for race day.
Mercedes' Lewis Hamilton spoke of the tyre's "melting and graining", while Toro Rosso's Brendon Hartley and Haas" Kevin Magnussen compared the compound to "bubble gum".
Romain Grosjean shared his team mate’s assessment.
"I thought it was raining at one point!” said the Frenchman.
"It was very, very difficult. Over one qualy lap it is always a decent tyre, but whenever you want to do a long run, you do three laps, and then it is like driving in the wet."
Ferrari’s Sebastian Vettel agreed that tyre management in qualifying will be paramount.
"That will be the main job to get right tomorrow because you have one lap in qualy," said the German.
"With the hypersoft it should be a bit easier but still it's quite tricky to keep a clean balance from the beginning to the end of the lap."
Pirelli F1 boss Mario Isola admitted that Saturday’s free practice session will provide a final opportunity for teams to get a final handle on the hypersoft’s degradation.
"It was quite a tricky day to interpret, although in many ways a bit similar to what we saw in Mexico last year," said Pirellli F1 boss Isola.
"Today, there was high degradation on the hypersoft in free practice, which is of course two steps softer than the softest compound we brought to Mexico in 2017 (the ultrasoft).
"If this continues throughout the weekend, it will influence qualifying strategy, with some teams perhaps choosing to prioritise durability over outright pace, and a few different strategies presenting themselves for the race.
"A lot more data analysis is needed tonight and FP3 to fully understand the situation," he added.
"There’s a chance of rain on Saturday night, which would obviously ‘reset’ the track and wash away the rubber that’s been deposited so far.
"In any case, it already promises to be a great fight over the rest of the weekend"
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