'Arms race' to decide 2015 title - Vettel

May 7 (GMM) Mercedes is now set for a head-to-head fight with Ferrari starting in Barcelona this weekend.

That is the view of the reigning world champion team's F1 chairman Niki Lauda, who is certain Mercedes no longer wields a horse power advantage over the resurgent camp in red.

"Ferrari has closed the gap from last year to this year to zero," the F1 legend said in an interview published by Red Bull.

"I think they increased their engine by about 45 horse power, so my estimate at the moment is that they have the same engine power as the Mercedes has and now it depends on the car and what the drivers can do," Lauda added.

If that is true, then the speed of in-season development will be especially crucial as the European phase of the calendar now begins.

Germany's Bild newspaper says Ferrari has brought new wings, floor and engine software to Barcelona, which in the Maranello simulator showed a three to four tenths per lap improvement.

Mercedes, meanwhile, has a new floor, brake ducts and front wing endplates in its luggage, but for now is sticking with the same engine configuration.

"Our engine is as reliable as a Mercedes should be," boss Toto Wolff told Sport Bild. "So there will be no new unit in Barcelona."

But Ferrari's Sebastian Vettel is not sure even a big Barcelona package for the SF15-T will be enough to overtake Mercedes.

"Mercedes still have the strongest package," he insisted to Welt newspaper, adding that Ferrari is trying to eat into that advantage through a series of "small steps".

"The development arms race always decides the world championship," Vettel explained.

"If you do not improve from the first to the last race, you never win the title, even if you start with clearly the best car.

"We want to catch Mercedes," he told Sport Bild, "even if this is a very ambitious goal."

Mercedes' Wolff agrees with Vettel that the German team needs to keep improving if it wants to stay in front of Ferrari.

"We take Ferrari as an opponent very seriously," he said, "so we will be bringing any sort of update to the car as quickly as possible."

Finally, Wolff also backed Nico Rosberg to bounce back, even though many observers say teammate Lewis Hamilton already has him firmly under control in 2015.

"Even last year he was often written off and he always came back," said Wolff. "So I would be very careful not to say that it will be difficult for him now."