Sebastian Vettel is under no illusion that Mercedes will be hard to beat at Silverstone this weekend, despite finishing ahead of Lewis Hamilton in Friday practice.
Vettel said the most telling lap times from Mercedes were the long runs its drivers managed in first practice.
"I don't know what happened to them [today," Vettel said, "but we saw the pace in general with them during a long run in the morning, so they will be quick no matter what. Everything else will be a surprise, but if we can repeat it [being ahead of a Mercedes] tomorrow then we will see."
Vettel said he still had some fine tuning to do to get the most from his Ferrari.
"I think we didn't have any issues with the car and we got through everything that we wanted to do, but I'm not entirely happy yet with how the car feels and we need to make a step forward.
"I do [have a good sensation], but I think we can improve. We tried a couple of things and we need to find out what was good and what was bad and then put all the good things on the car."