Nico Rosberg has warned Mercedes' rivals that the world champions "are still holding back" after two days of winter testing.
Rosberg completed a mammoth 172 laps on Tuesday, taking Mercedes' tally over two days to 328. He finished fourth in the standings on a medium tyre lap, behind Sebastian Vettel and Daniel Ricciardo's super-soft times and a lap from Sergio Perez on super-softs.
The German driver says it would be foolish to read into Mercedes' times at this stage.
"It was a great day," Rosberg said. "I was excited to get in the car again and go flat out. It was a real Formula One marathon today, lots and lots of laps and kilometres because we need to do that to push the car to its limits and find little problems with the car.
"At some point something will break but for now nothing is broken so we need to keep on going with laps and see where the weak points are. Lap time is not realistic to where we are so far and we haven't shown our cards yet as we are still holding back. For sure the car is quick and the opposition seems to be quick. How quick we are nobody knows for now but of course we are confident."
Rosberg, who took over from Lewis Hamilton, ran a Mercedes with a radical new bargeboard design. It came after Toto Wolff promised the team would be running some "unusual" parts in winter testing, with a new nose expected on the car tomorrow.
Rosberg has praised Mercedes for its innovative upgrades and thinks it could help Mercedes retain an edge on its rivals.
"We have a real innovation on the floor which looks quick futuristic and I am very excited about that. It is important for us to be innovative and be one step ahead of the others because it is easy to copy. When they see the things on our car they will take them and automatically go faster so we have to try and be one step ahead."