Sep.23 (GMM) Sebastian Vettel's early test for his 2009 employer Red Bull Racing was about more than just allowing the German to acclimatise to the Renault-powered team.

That is the claim of retiring RBR racer David Coulthard, who says the Milton-Keynes based squad was also keen to learn about why it has fallen behind the pace of Red Bull's junior team, Toro Rosso.

Vettel, 21, won the Italian grand prix from pole just over a week ago, leading some to wonder if Toro Rosso is simply reaping the benefits of a better Ferrari engine with a near-identical Adrian Newey-penned chassis.

Writing in his online column for ITV, Coulthard said of Vettel's Jerez test: "The other aim was to help crystallise what the differences are between the RB4 chassis and the STR3 that Toro Rosso use, in terms of grip, driveability and so forth."

37-year-old Coulthard said Vettel's race-winning form was the perfect opportunity for him to compare the teams' respective cars and give feedback about other reasons for the performance differences.

"So it was a useful exercise for both Sebastian and the team," said the Scot.