Rain on Sunday morning, low cloud and cold temperatures are likely to make for a damp (if not fully wet) start to the Chinese Grand Prix. If the rain returns, all bets are off in terms of strategy, with Sunday set to become the first meaningful running on Pirelli's new, wider extreme-wet and intermediate tyres. The extreme-wets are actually entirely new for this weekend, with Pirelli bringing a new compound that did not feature during the wet-weather test in Barcelona earlier this year.
"We have a new extreme-wet that is different compared to the Barcelona tyre only on the tread compound," Pirelli's Mario Isola told ESPN. "Of course the construction and the tread pattern is the same. We decided to develop and ask for the authorization to use the tyre in specific circuits where we expect cold conditions or because they are low severity circuits, so the amount of energy that is going into the tyre is less than expected and we struggle a little bit to warm up the tyre, so we need to generate grip when the tyre is cold. We have the standing start in case of a wet race this year, so we prefer to supply to the teams a compound that is able to generate grip earlier compared to the standard one.
"The biggest difficulty with the wet, but also with the intermediate tyre, was that you have only one product for 20 different circuits. You go to Malaysia where you have 30 degrees and also when it is raining, and it was in the past a high severity circuit. Now after the resurfacing it is a little bit less, but still a high severity circuit. And then you go to other circuits that are low severity in condition and you are not able to generate grip. So we need two different products. We discuss that with the teams in the past and we agreed that a good solution could be to supply two different compounds."
With no practice running on Friday, judging how race strategy will pan out in a dry race is a bit of a guessing game. But Pirelli's simulations before the weekend suggest a one-stop race is the way to go.
"If the level of degradation is as low as we expect, it is a one stop," Isola said. "The difference compared to Melbourne is that in Melbourne the delta lap time between the soft, super-soft and ultra-soft was less than one second. We had something around 0.8 on Friday, and 0.6 between the super-soft and the ultra-soft, so the difference was not huge.
"Here we have the medium, the soft and the super-soft. And we have seen in Barcelona between the medium and the soft the gap is bigger. It is more than one second. Our estimation is that it is probably around 1.5, 1.6 seconds per lap. While between the soft and the super soft should be more or less the same as we have seen in Melbourne, so around 0.8, 0.7. this means that teams are probably more oriented to use the soft and the super soft because the medium is a bit far away compared to the other two."
Front-tyre graining has historically been the limiting performance factor that prompts teams to pit for new tyres in Shanghai. However, Pirelli believes it has reduced its rubber's susceptibility to graining with the latest generation of tyres, meaning tyre wear -- and the decision to pit -- may no longer be limited by the state of the front tyres alone.
"Tyre wear is much more balanced this year because without the graining you have a combination of degradation, there is a thermal degradation coming from the rear, and very low abrasion coming from the front," Isola said So it is much more balanced compared to last year.
"If we look at China last year, the main limitation was the graining. Especially on the softer compound choices. So when we were talking about the wear life of the tyre it was because with the graining on the front you have accelerated wear. If you don't have graining, and the degradation so low, you can run a much longer stint also on the softest choices. That means that probably -- probably because we saw no running of dry tyres -- it is possible to have a race with just one stop, one set of super-softs used for quali, and one set of softs to finish the race."