LONDON, England - Formula 1 champion Sebastian Vettel has insisted that he is not the overwhelming favourite for the 2013 title and believes his main threat could come from Red Bull team mate Mark Webber.The season will howl into action on March 17 in Melbourne with 19 races scheduled over nine months with the season finale in Brazil on November 24 2013.'USUAL SUSPECTS'Vettel at 25 the youngest driver to win a hat trick of titles, said: "It's one thing to look back at what we have achieved as a team but really I feel that we all start again from zero. So we've all got the same chances and it will be a long year, a lot of races and a very tough challenge for all of us."It will be tough - tough to beat Mark (Webber), tough to beat the other guys and the other teams because they will try everything to beat us. The best drivers are in the best teams. I think it's easy for you to work out who they are. Fernando (Alonso) certainly is one of them."Mark is one of them, Lewis (Hamilton) is one of them and there are others, but I usually don't like to name them as there's a chance of forgetting one of them and that's not the idea. I think it's the usual suspects."Red Bull unveiled its car for the 2013 season with team boss Christian Horner saying the desire for more success was as great as ever.'CRACK AT CHAMPIONSHIP'He said the team was happy to have extended Webber's contract, though he had won only three races in the last two seasons."If we weren't happy with Mark we would never have signed him for this year. We give both drivers equal opportunity and it's down to what they do on the circuit and we'll continue to do that. It doesn't matter which driver wins as long as he's in one of these cars."Webber was confident he could beat Vettel to the title: "I do believe I can have a crack at the championship again this year. That's what I'm getting up each day thinking."