Rosberg encouraged by tyre performance

The German, who has been signed up to race alongside Mark Webber next season, admits he is still getting himself up to full speed with F1 machinery but is pleased with how his running is going.

"Generally I have been positively surprised by the Bridgestone tyre test," he told autosport.com after Sunday's simulated wet running. "In Barcelona although we did some running there, it was very difficult to assess as the temperature was so low.

"The wet test was fantastic and together with (Toyota's) Ricardo Zonta we have covered so much mileage.

"What was so educational was the electronics control systems. I have so much to learn but I have completed the wet programme, and it was a very good test."

Rosberg has said that not everything is perfect, however, because of mechanical dramas that have affected his recent running at Jerez.

"We've had a fair share of problems here, so we did not get much running," he added. "But I am pretty confident in the car. The handling is fantastic and I think I have been the fastest of the V8 runners for the past three days."

Williams are also working on modifying Rosberg's seat for the team's next test, as it is currently slightly too small for him.

"It is not quite perfect and it needs adjusting a bit," he said. "We will have to change it for the next test."