Pirelli says it is proving difficult for teams to simulate the 2017 downforce levels on the mule cars being used to text next year's F1 tyres.
Mercedes, Red Bull and Ferrari have all supplied updated 2015 cars which are designed to have increased levels of downforce to simulate the performance of next year's cars.
Next season's lap times are expected to be at least five seconds faster compared to Barcelona 2015, but Pirelli motorsport boss Paul Hembery told F1i it is difficult to achieve the required balance between downforce and drag.
“That’s it, it’s two-fold," Hembery said. "It’s not a new car project for the teams, it’s not as if they’ve approached it as if it’s a car that is going to go into race form. So they’re using a number of techniques to try and achieve that down load but sometimes you do that and you slow the car down too much.
"To be honest what we saw with the Toyota if we go back a few years, we had the Toyota and in the second year of testing we just tried to get the down load up and what happened was the car became so slow in a straight line because of the drag that it wasn’t achieving what we needed."
Despite the difficulties, Hembery says the work being carried out - which included both Ferrari and Mercedes testing at different venues this week - is crucial and praised the teams for their commitment.
"I have to say thought that the three teams involved have done a fantastic job so far and the rest of Formula One needs to thank them for actually putting the money up and working with us to get the product ready that Formula One wanted for next year."
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Scene at the Italian Grand Prix
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