Despite winning seven world titles, Michael Schumacher says he still suffers from self-doubt whenever he sits in a Formula One car.

"Despite my successes I have not lost the doubts about myself. Anything else would be the first step in the wrong direction," the Ferrari driver said in the build-up to the start of the 2005 season on March 6 in Melbourne.

"I have doubts whenever I sit in a racing car and at other times too. I think it's part of my make-up," the German said in an interview.

"I am a great doubter, I question myself all the time although I don't take it too far, I don't tear myself apart with these thoughts.

"I know when the doubting has to stop."

Schumacher has won the last five drivers' titles with Ferrari, who launch their new car today although they are due to continue with a modified version of their old one until the Spanish Grand Prix in May.

The 36-year-old, now the oldest driver on the Formula One starting grid, said his desire for success remains undimmed.

"I want to win the world championship although I know it will be harder than in any previous year," he said, picking out Renault and McLaren as his team's greatest rivals.

"We have managed to fend off defeats for five years. If we cannot achieve that any more, then so be it.

"I know that our run will end some time and someone will turn up who drives faster than me. I must live with that."