Pirelli's tyre test in Bahrain has been marred by a tyre blow-out, according to a tweet from Mercedes driver Nico Rosberg. The Italian company are to continue as Formula One's tyre supplier during the 2014 season and Red Bull, Ferrari, Mercedes and Toro Rosso have all taken part in a three-day test at the Sakhir circuit to test the new rubber. Nico Rosberg tweeted from Sakhir he'd spun at 320km …