Button: We need more pace

"We've improved a lot but still we're not where we want to be," the 27-year-old driver told Reuters on Monday after the unveiling of Honda's new 'Earth Car' livery aimed at increasing environmental awareness.

"We still have another test in Bahrain where we have a lot of things to test. Hopefully they are going to help the car because we are not on the same pace as the Ferraris, the McLarens or the BMWs."

Button took his first grand prix win with Honda in Hungary last August and had sounded optimistic about a championship challenge before the new RA107 ran for the first time in Spain last month.

But the car's subsequent performances in pre-season testing have been lacklustre compared to the speed of rivals.

The Formula One grapevine is already buzzing with speculation that Ferrari, with Finland's Kimi Raikkonen replacing retired seven-times champion Michael Schumacher, could be stunningly quick in Melbourne.

McLaren, with double champion Fernando Alonso switching from Renault, have also been early pacesetters although a question mark remains over their reliability.

Button was seventh quickest in testing in Bahrain on Saturday, with team mate Rubens Barrichello sixth, and returns to the Middle East for further testing on Tuesday.

"I don't think you can really tell too much from the lap times in testing," said the Briton. "I feel the initial car was not quite where we wanted it to be but we've definitely improved.

"We understand the car a lot more on these tyres, because that was the major issue; it's just finding our way on these tyres."

Honda have switched to Bridgestone this season after Michelin's withdrawal left the Japanese tyre brand as the sport's sole supplier.

"We're not quite there...but all we can do is get our heads down and hopefully improve the car as soon as possible," said Button. "We are definitely going in the right direction."