Jenson Button knows how it feels to step into a dominant Formula One car and leave envious rivals stunned by his lap times.

The Briton did that two years ago, when he tested for Brawn GP at Barcelona in his astonishing 2009 championship-winning year, but it is a sensation the 31-year-old has yet to experience with McLaren.

The team started last year off the pace and, with the 2011 season-opener looming in Australia on March 27 and just one more preseason test to come in Barcelona next week, McLaren's new MP4-26 has also failed to set the world alight so far in testing.

"When I first jumped in it (the car) the first reaction was not 'Wow, we're going to blow everyone away'. No," Button said after a day of filming and giving high-speed "taxi rides" in McLaren's new MP4-12C sportscar at an airfield circuit in southern England.

"I don't think anyone would have felt that because it's got a lot less downforce, the (Pirelli) tyres are working very differently to the previous (Bridgestone) tire," he said, attributing much of the difference to regulation changes since last season.

"But there's nothing that really scares me about the car in a negative way, so there's a lot we can improve with this car through general set-up work."

The former champion was the last of the top teams to bring its new car to the test track and it had a troubled debut in Jerez last month, with reliability problems limiting the amount of track time for Button and 2008 world champion Lewis Hamilton.

At the subsequent test in Barcelona, it again lost precious time while champion Red Bull, Ferrari and Renault all looked quick and did double the mileage.

"This year, at the moment, we've had some issues in testing in terms of getting parts to the circuit and a couple of reliability issues, so we've not done as much running as we would have liked, which has hurt our set-up work," said Button.

"But we do have four days and hopefully everything's going to run sweet at the next test and we get a lot of laps in and we can improve the base that we have.

"There's a lot still to extract from this car that we haven't because we just haven't had time to do it, we haven't got everything together yet, so we don't really know where we are compared to the competition," said the Briton.

Button won two races last year, including Australia for the second year in a row, while Hamilton was victorious in three. Mercedes-powered McLaren ended the season as runner-up to Red Bull and hungrier than ever to turn the tables.

"Of course we'd love to have had more mileage," Hamilton said of the team's testing so far. "I think we've good things coming in the pipeline, and we've definitely improved in the last couple days, we got 107 laps (in one day) at the last test," said the 26-year-old.

Hamilton said the new car was closer to the 2009 one, a chassis that started the season off the pace before rapid improvement, than his 2008 title-winning one in terms of grip due to the new tires and changed regulations.

However, it was a lot easier to handle.

"The '09 was terrible because the car was hopping, three-wheeling through corners, it was locking up, and it had no downforce," said Hamilton.