Sebastian Vettel's fourth title bid faces triple-edged threat

Sebastian Vettel's bid to become only the third driver to rack-up four successive world titles faces a triple-edged challenge from Ferrari, McLaren and Mercedes in 2013.

The German Red Bull driver was crowned the youngest three-time champion in 2012, grabbing the championship from Ferrari's Fernando Alonso by just three points in a breath-taking season-finale in Brazil after a roller-coaster campaign.

Vettel and Red Bull, whose lacklustre performance in pre-season winter testing was masked by sleight of hand fuelling to keep rivals guessing, will start the 19-race campaign as favourites.

Ferrari and McLaren will, as always, be closely tucked in, but Mercedes, with a bank-busting budget and with Lewis Hamilton having replaced Michael Schumacher, are widely-expected to smash through the three-team dominance.

Hamilton and Nico Rosberg, who consistently out-paced the ageing Schumacher in 2012, set the fastest times in testing in Barcelona, while former champions Alonso and McLaren's Jenson Button, were just off their shoulders.

Hamilton, the 2008 champion, insists his first year with the German giants will be a learning curve and that teams' strengths and weaknesses will not be apparent until the season-opener in Melbourne on March 17.

"I don't think there are any expectations," Hamilton told autosport.com.

"If anything, I feel like I have a free ticket. It's a year where we know we may not have the best package, but it's a challenge for me.

"I think the pressure is more on the other guys, who had great cars and were evolved into this year's car. They have the pressure to go and compete and perform. For us, we only have everything to gain."

Vettel, looking to emulate Juan Manuel Fangio and Schumacher as a four-in-a-row champion, was only eighth fastest in testing at Barcelona last weekend.

His test, as well as that of teammate Mark Webber, saw the Red Bulls run full of fuel and with 2012 having seen a dip in their dominance -- seven wins compared to 11 the year before -- Vettel is keeping his feet on the ground.

"We're in good enough shape I think. Overall testing has been good for us and we didn't have too many problems," said the German.

"But if you sum up all three tests I think all the teams were linked in to what the tyres could do and at times it was extremely difficult to read the set-up changes.

"I'm looking forward to Melbourne now and can't wait for the racing to begin."

The starting grid in Australia will see 11 teams and not the 12 of a year ago after Spanish strugglers HRT went to the wall of the global economic crisis.

Reflecting the sobre financial climate will be the appearance of more pay-drivers, those men fortunate enough to have courted wealthy patrons or been born into moneyed circumstances.

Britain's Max Chilton, whose father is believed to have banked around £70 million when he sold his stake in an insurance company, will debut for Marussia.