Sebastian Vettel not yet a great - Sir Jackie Stewart
Former F1 champion Sir Jackie Stewart does not believe Sebastian Vettel can yet be called one of the greats, even if he wins a third straight title.
The Red Bull driver won his fourth race of 2012 in Korea last weekend to take the lead in the drivers' standings.
But Stewart told BBC Sport: "If you've got a superior car, it's relatively easy to win the championship.
"To really show you're one of the greatest, you have to deliver when you haven't got the best machinery."
The three-time world champion added: "I have the highest respect for Sebastian, but he could not have achieved what he has without the [Red Bull design chief] Adrian Newey factor."
This season Red Bull initially struggled for pace and reliability and up until the 14th grand prix Vettel had won just one race - round four in Bahrain - to trail championship leader Fernando Alonso of Ferrari by 39 points.
But Red Bull then improved their car and the 25-year-old has since become unbeatable, winning in Singapore, Japan and Korea to take a six point lead from Alonso with four races to go.
"I'm a big Sebastian Vettel fan," added Stewart. "He completely dominated the Korean Grand Prix and drove in such a mature fashion for a 25-year-old. It was more than impressive.
"Vettel has established himself as the favourite and Alonso is now on the back foot.
"Led by Adrian Newey, Red Bull have bounced back from a slow start to the season and have now come up with superior equipment."
On Monday, BBC Sport linked Vettel - who is two wins away from equalling Stewart's record of 27 career victories - with a move to Ferrari in 2014.
But Stewart said: "I think that's premature. He would be mad to leave Red Bull at the present time.
"I know there would be a difference in their basic salary, but he's in a position where he's winning grands prix.
"He's won 25 races and is going to knock me off my perch before the end of the season - but he's only 25 and still has time to move."