Wolff giving Bottas four races to deliver the speed

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Valtteri Bottas inherited a plum drive at Mercedes after Nico Rosberg's retirement but the Finn will need to deliver the goods quickly, says Toto Wolff.

As Bottas and team Lewis Hamilton enter their last day of pre-season testing, the pair appear to be working well together at Mercedes.

Mercedes AMG F1 non-executive chairman Niki Lauda is pleased with how Bottas has settled in with the German squad.

The new recruit is still finding his marks and remains outpaced by Hamilton for now, both on the short and long runs, according to Lauda.

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Like his colleague and countryman, team boss Toto Wolff is giving Bottas four races to unleash his speed.

"Valtteri does not have a lot of time to prove he can be at Nico's level, to perform well against Lewis Hamilton and help the team keep up the development direction and speed in the car," Wolff said.

"It is clear that Valtteri needs to learn how to swim quickly."

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Phillip van Osten

Motor racing was a backdrop from the outset in Phillip van Osten's life. Born in Southern California, Phillip grew up with the sights and sounds of fast cars thanks to his father, Dick van Osten, an editor and writer for Auto Speed and Sport and Motor Trend. Phillip's passion for racing grew even more when his family moved to Europe and he became acquainted with the extraordinary world of Grand Prix racing. He was an early contributor to the monthly French F1i Magazine, often providing a historic or business perspective on Formula 1's affairs. In 2012, he co-authored along with fellow journalist Pierre Van Vliet the English-language adaptation of a limited edition book devoted to the great Belgian driver Jacky Ickx. He also authored "The American Legacy in Formula 1", a book which recounts the trials and tribulations of American drivers in Grand Prix racing. Phillip is also a commentator for Belgian broadcaster Be.TV for the US Indycar series.