Nick Heidfeld believes 2008 was the "most difficult" campaign of his entire career in motor racing.

The 31-year-old German spent his junior days in Formula Ford, F3 and F3000, and throughout his nearly ten years in F1 has driven for struggling teams including Prost and Jordan.

But despite his podiums and fastest laps this year, not to mention his new contract for 2009, Heidfeld often struggled to keep up with his BMW-Sauber teammate Robert Kubica.

"In terms of what I was able to get out of the car, it was definitely my most difficult year," he told spox.com.

"Not only in formula one, but in my whole motor racing career. I cannot remember ever struggling as much as I have done," Heidfeld said.

His problems have mainly originated in qualifying, where he has managed to outpace Kubica just four times out of the 17 races so far in 2008.

Heidfeld said: "I have had the best car that I have ever had the opportunity to race, but just this year I could not get everything out of it. Of course it was annoying."

It would have been even more annoying if it had cost him his seat, but Heidfeld was able to recover his form with the support of the team.

"I am now pretty happy," Heidfeld said, "because I have come out from a very difficult situation, even if it took longer than I expected.

"I am also content with the way I dealt with the situation. Although I obviously had major problems with qualifying, I never lost my head in the races and always got the most out of it."

Source: GMM