Toro Rosso debutant Brendon Hartley will run with number 39 at this weekend's United States Grand Prix.
Porsche World Endurance Championship racer Hartley, a former member of the Red Bull junior scheme, has been drafted in to compete for Toro Rosso at Austin, with Carlos Sainz Jr. moving to Renault and Pierre Gasly battling for the Super Formula title.
Under Formula 1 regulations, introduced in 2014, drivers run a personalised number between 2 and 99, with 1 reserved for the defending champion, should they wish to use it.
Hartley's STR12 will be adorned with 39, one of the test numbers allocated to the Faenza-based squad.
Hartley will be the first New Zealander to compete in Formula 1 since Mike Thackwell in 1984.
Hartley will partner Daniil Kvyat, who was benched for Malaysia and Japan, in order for Toro Rosso to evaluate Gasly.
Discussion about this post