Mercedes offered a glimpse of its true potential at the first day of the final pre-season test in Barcelona this week, as Nico Rosberg set a 1:23.022 on a qualifying-style run.
The world champions split their running between their two drivers, with Rosberg driving in the morning and team-mate Lewis Hamilton taking over in the afternoon. Rosberg's time was set on soft tyres and was just 0.212s off the best time of last week, which was set by Sebastian Vettel's Ferrari on ultra-soft tyres.
"We were doing qualifying practice this morning," Rosberg explained. "It's all the more enjoyable, to take the car to the limit. " We took some fuel out for once which was nice for me to get in to it to be able to push some more, so we put down some lap times and it was a good feeling."
Hamilton jumped in the car in the afternoon and completed a race simulation before setting his best time on medium tyres at the end of the day. Hamilton's effort of 1:25.051 was only good enough for sixth, but he will get his chance to drive the W07 on low fuel later in the week. Combined, the two Mercedes drivers managed 171 laps.
Asked how Mercedes compared with Ferrari, Rosberg said: "It's close out there between the two teams I think. It's difficult to know where [we are] exactly but they've done a great job so we need to really give everything because they are very close and a big threat. But of course we are confident and we are ready for a battle, for sure."
Ferrari's test day was less impressive, however. Kimi Raikkonen set the fastest medium tyre lap time with a 1:24.836, but was restricted to just 71 laps. He completed 42 laps before lunch as Ferrari focused on aerodynamic work and a series of set-up changes, but came to a halt at the end of the pit lane with a gear selection issue as the session resumed in the afternoon. The SF-16H remained in the garage until the final 90 minutes when it re-emerged and clocked up another 29 laps.
After flying under the radar for most of the first test, Williams indulged in some laps on the ultra-soft tyres on Tuesday afternoon. Valtteri Bottas used the new compound to set the second fastest time -- 0.207s off Rosberg on the soft tyres -- but more importantly finished the day with a healthy 123 laps.
McLaren used the time between tests to complete a filming day in an attempt to ensure the hydraulic and coolant leaks of the first week were fixed. Things appeared to be going well in the morning, but just before the lunch break Fernando Alonso stopped at the pit exit with a telemetry glitch. The problem was fixed by the afternoon and in the final hour Alonso set the third fastest time with a 1:24.735 using the soft tyres.
Red Bull also saw its track time limited on Tuesday after Daniil Kvyat returned from one of his morning runs with a rear brake on fire. The team made changes to the brake ducts in the afternoon and he returned to the track to finish the day on 69 laps.
"Yes we had a little issue with a brake duct, and we took a little bit of time to understand it and sort it out," Kvyat said. "But the guys did a good job because the rest of the day there was absolutely no issues."
With a new livery painted on his Toro Rosso, Max Verstappen managed a total of 143 following the official launch of the STR11. The car first ran in an all-blue paint scheme last week and continued to look competitive in its new colours. Force India's Nico Hulkenberg also focused on mileage with a series of long runs resulting in a total mileage of 121 laps by the end of the day.
The new Sauber C35 finally made its testing debut on Tuesday and Felipe Nasr racked up 102 laps behind the wheel with the ninth fastest time. That put him ahead of Kevin Magnussen in the Renault, who completed 119 laps before stopping in the final 15 minutes at Turn 3 and causing a late red flag.
Haas' second week in F1 got off to a disappointing start with just 23 laps due to a fuel system issue. However, Esteban Gutierrez was still quicker than Rio Haryanto, who sat out of most of the morning session with an oil leak.
Times
1. Nico Rosberg - Mercedes - 1:23.022 - 82 laps (morning)
2. Valtteri Bottas - Williams - 1:23:229 - 123 laps
3. Fernando Alonso - McLaren - 1:24.735 - 92 laps
4. Kimi Raikkonen - Ferrari - 1:24.836 - 71 laps
5. Daniil Kvyat - Red Bull - 1:25.049 - 69 laps
6. Lewis Hamilton - Mercedes - 1:25.051 - 89 laps (afternoon)
7. Max Verstappen - Toro Rosso - 1:25.176 - 144 laps
8. Nico Hulkenberg - Force India - 1:25.336 - 121 laps
9. Felipe Nasr - Sauber - 1:25.493 - 103 laps
10. Kevin Magnussen - Renault - 1:25.760 - 119 laps
11. Esteban Gutierrez - Haas - 1:26.661 - 23 laps
12. Rio Haryanto - Manor - 1:226.625 - 45 laps