After a short 16-week offseason, Formula One is back on track this week in Melbourne Australia.

Once again, the big question at the start of the season is: Can anyone dethrone Sebastian Vettel and Red Bull?

Vettel and Red Bull will attempt to win the drivers' and constructors' championship for the fourth consecutive year. The 25-year-old German is certainly the favorite to win the title this season, but his campaign for another championship might be just as tough, if not tougher, than it was this past year.

Fernando Alonso and Ferrari are starting off this season with much more optimism than they had one year ago, and Lewis Hamilton is set to begin his first season with Mercedes after spending the past six years with McLaren.

Following 12 days of pre-season testing in Barcelona and Jerez, Spain, Red Bull looks strong heading into the season-opening Australian Grand Prix, as Vettel and his teammate, Mark Webber, were among the fastest in testing. But Mercedes was the most impressive in Spain, with Nico Rosberg and Hamilton posting the quickest times in four of the 12 days. Ferrari, Lotus and McLaren weren't too shabby as well.

While testing was merely a dress rehearsal for the upcoming season and a chance for the 11 teams and 22 drivers on this year's F1 entry list, no one is quite certain who will perform the best throughout the year.

Drivers and teams are eager to arrive in Melbourne to find out who has the right stuff and who might be in trouble this season.

VETTEL'S BID FOR FOUR

After finishing the 2012 season only three points ahead of Alonso, Vettel became just the third driver in F1's 63-year history to win three successive world championships. Juan Manuel Fangio won four titles in a row from 1954-57, while Michael Schumacher, who retired from the sport for good at the end of last season, captured five straight championships from 2000-04.

One year ago, Vettel and Red Bull didn't exactly burst out of the gate, like they did at the start of the 2011 season, when he and the team won six of the first eight races. He finished second in the other two. Vettel's first win last year didn't come until the fourth round in Bahrain.

Vettel needed a late-season surge to help him win his third title in a row. He rebounded from a 39-point deficit by winning four consecutive grand prix (Singapore, Japan, Korea and India).

During preseason testing, Vettel was pleased with the performance of Red Bull's car for 2013, the RB9.

"We managed to test quite a lot, but we also know that there is still a lot of room for improvement," Vettel said. "All in all, I am fairly happy with how everything went in these last weeks. The team did a great job with the car, and both Mark (Webber) and I felt comfortable right away.

"We haven't come across any big problems, and the smaller ones have been dealt with straight away. The RB9 has been so reliable that it's been a pleasure to drive. We learned a lot over the winter tests, and we'll be bringing that new knowledge with us to Australia."

The one big challenge that Red Bull and all other teams face heading into this season is the new Pirelli tire. This tire is heavier, but the compound is softer and faster than the previous one.

Based on testing, teams are uncertain how the tire will perform in Melbourne. Vettel said after his last day of testing that teams will need more time to better understand the tire. He also thinks it will be difficult to predict what will happen in the Australian GP.