Mercedes duo Nico Rosberg and Lewis Hamilton say they are still not completely happy with their W06 Hybrid, despite dominating Friday's practice sessions at the Australian Grand Prix.
Rosberg led Hamilton in both sessions, with Ferrari's Sebastian Vettel getting closest to the pair, albeit seven-tenths of a second down on his compatriot's best lap.
"I was very happy with my long run but on one lap I still need to work on the pace as I had a lot of oversteer in the car," said Rosberg, who won in Australia in 2014.
"It seems again that it's very close between Lewis and me and he is a great driver, so I need to nail the setup every time to come out on top. This year will be a big battle again against him, I'm sure."
Hamilton finished the second session exactly a tenth of a second down on his team-mate.
"There's a little bit of work to do on my side as I'm not 100% comfortable with the car - but that's to be expected on the first day," he said.
"Today seemed to confirm that we have pretty good pace. But there are still other quick cars out there and we can't go into tomorrow's sessions not thinking that they will be close."