Rosberg Expects to Finish Behind BMW

German racer Nico Rosberg has played down Williams' hopes of emerging as the third force in formula one this season.The Grove based team has enjoyed a positive winter period with its new Toyota-powered FW30, but 22-year-old Rosberg doubts that the single seater is yet ready to take on BMW Sauber for the 'best of the rest' honours behind Ferrari and McLaren.