Lots of laps

Ferrari completed 929 laps of the Barcelona circuit over the eight days of testing, equal to 4,324km - or more than 14 Australian Grand Prix distances. Mercedes managed 1,040 laps or 4,841km.

But Ferrari's fastest laps were set on the new hypersoft tires, the quickest type available, which Mercedes did not even take to Barcelona.

Ferrari also went quicker than Mercedes on the ultrasoft tires but slower on mediums, the best for long stints. Add in times set on different days, with a range of track temperatures, and the jury remains out.

The amount of smoke coming from the Ferrari in the pitlane in Spain will also be something to watch, with some suggesting their engine was using more oil than others.

Vettel, a four-time champion who won his titles between 2010-13 with Red Bull, played down the testing times.

"We are still working on some things for the first race and it's not really possible to make any predictions based on the performance of the other teams, because everyone is running a different program," he said.

"However, I'm happy for the guys in the team," added the German, whose preseason media engagements have been kept to an absolute minimum.

That has allowed the team to focus on the job in hand behind closed doors, even if some detect something of a siege mentality, and spare Vettel too much focus on his temperament after flare-ups in 2017.

Ferrari chairman Sergio Marchionne, who has also made headlines by suggesting Ferrari could leave the sport if they feel it is going in the wrong direction, is clear about what he wants to see.

"The best thing I think that could happen in 2018 is for Ferrari to perform up to its true potential and to take on the competition," he said last month after the company's fourth-quarter financial results.

"And especially Mercedes with whom it has a love-hate relationship, which goes back about four or five years. It would be great if we could see a proper fight between Mercedes and Ferrari."

Reuters