Newey was still 'designer' of 2015 Red Bull - Horner

After Horner and his 2015 drivers met with the media on Tuesday, Germany's Auto Motor und Sport said Horner put an actual percentage on the time Newey will spend on formula one from now on -- 50.

The other 50 per cent will be spent on projects like the America's Cup, but Horner said of the 2015-specification RB11: "He (Newey) is the designer of this car."

Horner revealed that Newey will also be at Jerez on Sunday to oversee the Renault-powered car's track debut, which will be driven around the Spanish circuit by Daniel Ricciardo.

But before then, Horner said, the team is still working hard.

Car still not ready for testing

When asked if the Jerez-spec RB11 is ready to run now, he admitted: "Not yet.

"We are flat out into car build at the moment, this is probably the shortest production and assembly time in our ten seasons."

Red Bull's late development of the 2014 car, and now pushing the time barriers with its successor, is undoubtedly because of the extent of Mercedes' dominance last year, with similar regulations still in play for 2015.

"Hopefully we will have made significant inroads into that advantage," said Horner.

Given the way Mercedes dominated last year, Horner's optimism was telling, and it was echoed by the team's new number 1 driver, Ricciardo.

"You'd like to think that Mercedes' room for improvement is smaller than everyone else's," the Australian said.

Worried about Williams

Another of Mercedes' challengers in 2015 will be the independent British team Williams, and Ricciardo said he expects them to be strong again this year.

"The big question mark is McLaren-Honda," he added. "Everyone will be watching to see what kind of step they can do.

"With Ferrari, there is no real sign they can gain a second a lap. McLaren, they could gain a second if it all gels with Honda," said Ricciardo.