May 21 (GMM) Robert Kubica has taken issue with suggestions that his teammate Nick Heidfeld is struggling simply with the setup of BMW-Sauber's 2008 car.



The 23-year-old Pole, who has outqualified his more experienced German teammate on all five occasions so far this season, insists he is just driving well.



Last year, in contrast, it was suggested that Kubica was struggling to keep up with Heidfeld because of the change to Bridgestone's control tyre.



But in a recent interview, he said blaming tyres is an oft-used "excuse" when comparing the performance of a team's drivers.



"I don't think it's a question of car," Kubica is now quoted as saying by F1's official website.



"I'd rather consider the fact that I now have one more year of experience and that I am working very well with my new race engineer, Tony Cuquerella," he added.



Kubica, meanwhile, offered no comment to speculation that - despite BMW's option on his services for 2009 - Ferrari may be interested in him for the future.



"I am currently a BMW-Sauber driver and my duty is to fight on track and try to beat everyone else," he said.