After months of preparation and testing, it's time for 11 teams and 22 drivers to get the 2013 Formula One season underway with this weekend's Australian Grand Prix.

There are a lot of unknowns heading into the opening round of the 19-race schedule this year. With teams still figuring out the new Pirelli tire, no one is quite sure what to expect in Australia.

Red Bull, Ferrari, McLaren, Lotus and Mercedes will once again be the top teams, but after winter testing in Barcelona and Jerez, Spain, no one is fully certain which one of those teams will perform the best throughout the season.

"I think it's going to be a long year," said Red Bull driver and three-time defending world champion Sebastian Vettel. "We're looking forward to this weekend, and this is the first of many. I think we've seen in the last couple of years, last year in particular, that it's a long season and every race is very important. So this is the place we start, but then there are many other places coming."

Vettel begins his campaign for a fourth consecutive title. The 25-year-old German beat Fernando Alonso from Ferrari by just three points for the title last year. Vettel won the Australian GP for the first time in 2011. He finished second in this event last year.

The new tire will be a major factor in the Australian GP and perhaps other races to come. More pit stops for tires are expected since the 2013 compounds are softer and faster than the previous ones.

"No one knows who can win this race at this moment," Alonso said. "We have to wait and see for answers to some questions that winter testing doesn't answer. I think there are top teams with a little bit of advantage. Maybe it's not the same as last year where we saw seven different winners in the seven first races. It was a little bit mixed on the grid.

"I think this year with the consistency in the rules I expect the five top teams to have a little advantage and not to have many, many surprises in the first races."

Jenson Button from McLaren is perhaps the favorite to win the Australian GP, since he has three victories in the last four races at Albert Park Circuit in Melbourne.

"The start of a new season is always exciting, as it's the culmination of months of hard work and planning," Button said. "I've had some great experiences in Melbourne, having won the race three times, and I love the place. There isn't a better location in the world to be kicking off what will no doubt be a fiercely competitive world championship."

The Australian GP is the home race for Red Bull's Mark Webber and Toro Rosso's Daniel Ricciardo. Webber's best finish in this event is fourth, which occurred last year. He has also finished fifth in it three times.

"I think it's just great to come to Australia at any stage, let alone for a race, so we're all looking forward to finally racing," Webber said. "There's a lot of testing that goes on in Spain, and we can all get down to what we all enjoy doing, and that's racing the cars. All the teams, drivers come here with a little bit more anxiety, because it's the first grand prix of the year."

Ricciardo finished ninth in his first race in front of his home crowd one year ago.

Series: Formula One. Date: Sunday, March 17. Race: Australian Grand Prix. Site: Albert Park Circuit. Track: 3.3-mile (5.303-kilometer), 16-turn temporary street circuit. Start Time: 2 a.m. (et). Laps: 58. Miles: 191.110 (307.574 km). 2012 Winner: Jenson Button. Television: NBC Sports Network.