JEREZ, Spain — Red Bull unveiled its new Formula One car on Wednesday, calling it an “evolution” from last year’s design that challenged for the world championship.

Mark Webber drove the Austrian team’s RB6 car at the second session of preseason testing at Jerez Circuit.

“To be honest we finished last season with a first and a second, so we didn’t want to go to great lengths to design another car on the back of that or go too crazy,” Webber said. “I think there are a lot of subtle, small things that will hopefully make this car more successful than last year’s.”

The car’s front wing was reworked to incorporate a new rear diffuser, which the car didn’t have last season. A shark fin engine cover was added, in line with most of this year’s designs. The car is also longer to accommodate a larger fuel tank since refuelling during a race is banned this season.

Chief technical officer Adrian Newey called it a “sensible evolution” of the 2009 car with the double diffuser the big difference.

“We tried to refine and evolve it rather than go to new concepts,” Newey said. “The two main challenges were the larger fuel tank and the smaller front tire.”

Sebastian Vettel, who finished runner-up last year, says the team’s decision to skip last week’s opening session at Valencia would not be “a disadvantage” as long as it maximises its use of the remaining sessions.

“Most important now is that the car is running and that we improve the reliability and speed. First you need to make your car work, then you see where you are and according to that you set your expectations,” said Vettel, who was impressed with Ferrari and McLaren’s early form.

“For sure there is only one target, to be just one step better than last year. I want to win the world championship. If we are the favourites, that’s fine. If not, that’s fine too,” Vettel said.

Although reliability was an issue, Red Bull still won six races last season — only two fewer than championship winner Brawn GP — with Vettel and Webber sweeping the last three.

“Red Bull Racing’s still a relatively young team and so the lessons that we learned last year will serve us well going into 2010,” team principal Christian Horner said. “We’ve had stability over the winter and continuity in all areas, so I think we’re in good shape.”