May 14 (GMM) Team boss Mario Theissen has defended the performances so far in 2008 of BMW-Sauber driver Nick Heidfeld.

The experienced German driver has been outqualified by his teammate at every event so far this season, and he only outshone Robert Kubica in the Australian grand prix because Kubica was shunted out of the race.

Theissen concedes that Heidfeld's results have sparked speculation about his future.

"But I have a very relaxed point of view regarding this issue," the German said, insisting that BMW's current driver lineup is "equal".

Theissen points out that, one year ago, it was Kubica who was struggling to adapt to life with Bridgestone's new control tyres.

He explains that, in 2008, 31-year-old Heidfeld's smoother driving style than the aggressive Kubica means he is struggling to get heat into the tyres for a fast qualifying lap.

"In the races, however, Nick makes us happy with his spectacular overtaking manoeuvres," Theissen insisted.

"Now we are going to analyse the entire package together with Nick to get to the bottom of the (qualifying) problem," he added.