Rosberg's best lap of 1m 35.697s put him just over three-tenths clear of namesake Nico Hulkenberg, second for Force India with a 1m 36.064s.
“Our main aim today was to try different directions with set-up and to get to know the tyres a bit better,” commented Rosberg. “You never stop learning how to get the best out of the tyres, so it has been a productive day from that perspective. We also did a bit of work on the brakes as this is an area I'm not one hundred percent happy with at the moment.”
Fernando Alonso was third for Ferrari. In the morning, the Italian team concentrated on fine tuning various electronic configurations and on taking aerodynamic measurements with constant-speed runs down the main straight. In the afternoon, Alonso carried out short runs to evaluate different set-up choices.
Despite making the team some lengthy set-up changes to his car between runs, McLaren’s Kevin Magnussen was the day’s busiest driver, the Dane racking up 102 laps without problem en route to fourth on the timesheet.
Just behind Magnussen was Williams’ Valtteri Bottas. The team reported a productive day, despite Bottas - who hands overs to reserve Felipe Nasr on Wednesday - only completing 28 laps in the Mercedes-powered FW36.
“We had good mix of tests today with aero, mechanical, car set-up, electronics and power unit, and we managed to get through everything which is hugely encouraging,” said Rob Smedley, head of vehicle performance. “The results were very positive and we collected a lot of good data, which is good news.”
Seventh fastest was Red Bull’s Daniel Ricciardo, who commented: “We didn’t get in any performance runs today but we did some good long runs in the afternoon with three set-up changes and we got some good feedback from that. I think during last weekend we struggled a bit in P1 and P3, the daytime sessions in the heat, but the car felt a lot better today in those conditions, particularly on those long runs.
“We’re still a little behind but we’re chipping away and I’m sure over the course of this test and in China we’ll get a little bit closer. For the moment, though, we’ll take every little bit we can get. We’re learning and we’re making progress.”
Each of the 11 F1 teams has agreed to dedicate one day of testing this year exclusively to tyre development work for Pirelli. On Tuesday it was Caterham’s turn, with test and reserve driver Robin Frijns at the wheel of the CT05. Unfortunately, a hydraulics leak just before lunch brought a premature end to the Dutchman’s day. Williams are Pirelli’s designated team on Wednesday.
Power unit-related problems limited Lotus’s Pastor Maldonado to just 16 laps, while at Toro Rosso, Daniil Kvyat was on driving duty as the team focussed on tyre and chassis work over long runs, aimed at developing the STR9 in race trim as well as giving the Russian rookie extra mileage under race conditions. He hands over to team mate Jean-Eric Vergne on Wednesday.
“Even if you can’t see it from looking at the timing screen, this was a productive day during which we learned a lot,” said Kvyat. “It was very useful for me, giving me a lot of laps away from the race weekend environment. We also learned something about why our pace was not as strong as we had expected in Sunday’s race. I think this in-season testing is a very useful thing, not just for the teams, but also for guys like me who have to catch up in terms of experience.”
Testing concludes in Bahrain on Wednesday.
Unofficial Tuesday times from Bahrain:
1. Nico Rosberg, Mercedes, 1m 35.697s, 121 laps
2. Nico Hulkenberg, Force India, 1m 36.064s, 69 laps
3. Fernando Alonso, Ferrari, 1m 36.626s, 69 laps
4. Kevin Magnussen, McLaren, 1m 36.634s, 102 laps
5. Valtteri Bottas, Williams, 1m 37.305s, 28 laps
6. Max Chilton, Marussia, 1m 37.678s, 60 laps
7. Daniel Ricciardo, Red Bull, 1m 38.326s, 91 laps
8. Sergey Sirotkin, Sauber, 1m 39.023s, 76 laps
9. Robin Frijns, Caterham, 1m 40.027s, 63 laps
10. Pastor Maldonado, Lotus, 1m 40.183s, 16 laps
11. Daniil Kvyat, Toro Rosso, 1m 40.452s, 67 laps