LONDON, ENGLAND - BMW-Sauber test driver Christian Klien said the interim Formula One car being tried out by the team in Spain this week was the ugliest he had seen.

The German manufacturer on Monday ran two modified 2008 cars on slick tyres and with some of the bodywork conforming to the 2009 regulations, a high and narrow rear wing along with a wide and low front end.

Klien's car was also fitted with the new KERS (kinetic energy recovery system) device that is being introduced next year.

"To me, for the moment, it's the worst Formula One car I have ever seen. It just doesn't fit together," the Austrian told the autosport.com website after the first day at Barcelona's Circuit de Catalunya.

"But we will get used to it. There will be a lot of modifications until the first race in March."

BMW-Sauber, who finished third overall this year, are due to launch their 2009 car in Valencia on Jan. 20.

"It drives quite well, actually," said Klien of the hybrid version. "There are still quite a few improvements coming over the winter. Basically it's quite a lot less downforce but with the slick tyres it compensates quite a lot."

Klien said the rule changes would slow lap times and pose a new challenge for drivers.

"Even with these aerodynamics it's still not possible to drive right behind another car," he said. "We will see in the first few races. It's more of a problem to not knock off the front wing at the first corner."

(Reporting by Alan Baldwin, editing by Tony Jimenez)