Heidfeld unhappy with form

BMW Sauber's Nick Heidfeld is concerned about his Formula One form after being outqualified five times in a row by Polish team-mate Robert Kubica.

"I find this year's car a bit more difficult to drive than last year's," the German told reporters at the Monaco Grand Prix.

"But I don't want that to be seen as an excuse because obviously we both have the same car.

"I think the main problem is over one lap, but even in the race it is not perfect. That's the way it is and we are obviously trying to improve things. I hope I will get on top of it," he added.

Kubica has scored four points more than Heidfeld in the season's five races so far and has been consistently quicker in qualifying, taking his and the team's first pole position in Bahrain in April.

That marked a turnaround from last year, when Heidfeld outperformed his team-mate.

"It is a bit of a concern because I don't like being slower than my team-mate and Formula One is my life," said Heidfeld.

"It's not a situation I enjoy being in at the moment. It sometimes can happen in Formula One, but unfortunately it doesn't make it any nicer."