Sebastian Buemi was behind the wheel of the new Toro Rosso for a day of testing in Jerez that was disrupted by intermittent showers.
The team took advantage of the changing track conditions to find out optimum switching points between the dry, intermediate, and wet tyres.
The team did have enough dry laps available to complete their planned evaluation of the brake system of the new STR5.
More rain is forecast for tomorrow, when Buemi continues testing duties for the team.
