Nico Rosberg said he felt tyre management will be the key challenge in Barcelona this weekend after the opening day of running ahead of the Spanish Grand Prix.
The German was third fastest after the two Friday sessions at Catalunya, with his best time being just three-tenths of a second slower than the quickest lap set by McLaren's Jenson Button.
However, the Chinese Grand Prix winner said he was concerned about tyre performance after the two sessions and said that managing the Pirelli rubber was going to be key to who emerged successful from the weekend.
"Generally all worked well today, but there are also a few question marks after the two sessions,” he said. “Tyre management will be a big challenge again this weekend, and that will be the key for success. We have got plenty of options to work though this evening to find the right set-up for the conditions out there tomorrow and on Sunday."
Team-mate Michael Schumacher – a critic of the Pirelli tyres in recent weeks - was eighth quickest and said the team needed to take a careful look at its data overnight to make the best approach to Saturday's qualifying session.
"The way it worked out for us today demonstrated that the testing we did in Mugello was worth it, so again I'm happy we had the chance to do that,” he said. “Of course it was very warm today and therefore the track was quite slippery, but that was according to our expectations.
“Our feeling for the weekend is pretty okay after everything we have learned in the two sessions, so we will now analyse the data carefully in order to work out exactly how to approach qualifying and the race from everything we have learned in the two sessions today."