Valtteri Bottas fastest on second day of F1 in-season test in Bahrain

SAKHIR, Bahrain -- Valtteri Bottas finished the second and final day of this week's in-season test in Bahrain at the top of the timesheets for Mercedes.

The two days at Bahrain's International Circuit were the first in-season test days of the season ahead of two more at the Hungaroring in August. In the heat of the desert, the lap times were a long way off Saturday's qualifying pace for the grand prix but teams were mainly focused on analysing new parts and gaining a better understanding of the tyres in Bahrain's extreme heat.

Bottas completed 143 laps in total despite causing a red flag midway through the day when the car stopped with a mechanical issue related to the steering wheel. The problem was quickly resolved once the car was returned to the pits and Bottas continued to rack up the laps throughout the afternoon, with a best time of 1:31.280.

Sebastian Vettel's Ferrari was 0.294s off Bottas after a relatively limited day of 63 laps. A lengthily stoppage came after just eight laps when the car returned to the garage for a planned setup change and a quick fix only to remain there for several hours following a power supply issue to the garage itself. That led to an extended period of downtime before systems checks were carried out and the car was able to reappear in the early afternoon to continue the team's testing programme.

Carlos Sainz was third fastest after taking over driving duties in the Toro Rosso from teammate Daniil Kvyat midway through the day. He was 0.604s off the pace of the Mercedes and completed 68 laps to add to Kvyat's 61. Stoffel Vandoorne was fourth fastest for McLaren-Honda following a much more promising day in which his best lap was just 0.828s off Bottas.

McLaren's racing director Eric Boullier dubbed Tuesday the team's best test day of 2017 after Vandoorne was able to push some of the car's settings without a repeat of the MGU-H issues the team has faced since arriving in Bahrain. But with only some updates to the power unit's ancillaries during the test, Honda is still unsure of the exact cause of its spate of MGU-H failures which will continue to be investigated.

Kevin Magnussen was fifth fastest as Haas continued to test new brake supplier Carbon Industrie ahead of a possible switch from Brembo at the upcoming Russian Grand Prix. The team has struggled with its brakes since it entered F1 last year and despite a successful update from Brembo at the Chinese Grand Prix, a switch Carbon Industrie could still be on the cards.

Esteban Ocon set the sixth fastest time after spending a morning in the Force India before handing over to teammate Sergio Perez. The team is waiting on a major update ahead of the European season, meaning it was mainly focusing on tyre and setup options with Perez clearly focusing on long runs in the afternoon.

Williams test driver Gary Paffett made his return to F1 on Wednesday following a four-year absence from an official F1 test. The 36-year-old DTM driver technically qualifies as a young driver under F1's regulations as he has never taken part in a grand prix. He completed a mammoth 126 laps with a best time within a second of Bottas.

Russian 21-year-old Sergey Sirotkin was at the wheel with the Renault and completed 90 laps in his new role as the team's test driver. He took over the team's test programme from race driver Nico Hulkenberg and was 0.281s quicker than Red Bull junior and Super Formula driver Pierre Gasly, who was limited to 65 laps because of an exhaust problem. Pascal Wehrlein was 11th fastest after completing 91 laps in the Sauber just two days after his full race return from a back injury earlier this year.

Times at close

1. Valtteri Bottas, Mercedes, 1:31.280, 143 laps
2. Sebastian Vettel, Ferrari, 1:31.574, 64 laps
3. Carlos Sainz, Toro Rosso, 1:31.884, 68 laps
4. Stoffel Vandoorne, McLaren, 1:32.108, 81 laps
5. Kevin Magnussen, Haas, 1:32.120, 88 laps
6. Esteban Ocon, Force India, 1:32.142, 60 laps
7. Daniil Kvyat, Toro Rosso, 1:32.213, 61 laps
8. Gary Paffett, Williams, 1:32.253, 126 laps
9. Sergey Sirotkin, Renault, 1:32.287, 90 laps
10. Pierre Gasly, Red Bull, 1:32.568, 65 laps
11. Pascal Wehrlein, Sauber, 1:34.462, 91 laps
12. Sergio Perez, Force India, 1:35.015, 70 laps