Lewis Hamilton reckons Mercedes still has progress to make despite their dominant start to the 2014 season.
Mercedes has been untouchable so far this year having claimed pole position and victory in all four races.
But Hamilton, who has won the last three races, believes his W05 is still lacking in some areas compared to Red Bull's RB10.
"We're not sitting comfortably that's for sure," he said. "We've got more work to do.
"The Red Bull is very, very fast through the high-speed, which tells me they maybe have a little bit more downforce than us."
Hamilton nonetheless thinks that Mercedes has closed the deficit they previously had to Red Bull in the aero department.
"Last year was a massive gap between how much downforce they had," he said. "We've definitely closed that up but I think we can do a better job, we can do more.
"So we're going to keep pushing on that and undoubtedly Mercedes are going to keep pushing and I feel comfortable that they'll keep getting better in terms of the engine."