BARCELONA (AFP) - Finland's Valtteri Bottas recorded the fastest time for Williams on day two of the second pre-season test in Barcelona as double world champions Mercedes enjoyed another promising session.
Bottas posted the fifth fastest time through six days of testing and the second quickest on the supersoft compound in 1min 23.261sec.
Two more days of testing remain in the Catalan capital before the first race of the season in Australia on March 20.
"That's it for me now for testing before we go to Melbourne. I'm feeling prepared and good in the car," said Bottas.
"I'm glad we have made progress during testing and I'm sure we will make even more before Melbourne."
World champion Lewis Hamilton was just over three tenths of a second back on a slower setup as he was released onto the soft tyres for the first time after piling up huge mileage in the W07.
The Englishman's time was six tenths of a second down on the best lap posted by Mercedes teammate Nico Rosberg on the soft tyres on Tuesday.
However, Hamilton was comforted by a visit from American ski speed queen Lindsey Vonn, who adorned the paddock on crutches a day after confirming her season is over due to a hairline fracture in her left knee.
"The car was good, quite strong, we did some lower fuel running today but some work needs to be done balance wise," said Hamilton.
"Getting onto the softer tyre was a good experience, but we've got some work to do still." Hamilton and Rosberg combined for another mammoth 164-lap day with the German completing a race simulation in the afternoon, albeit with only the ninth fastest lap time on the day.
"I did a full Melbourne race simulation and I feel well prepared now for the first race," said Rosberg.
"The car feels great out there and I haven't had a major problem yet. I hope this will continue for the last two days." Kevin Magnussen provided more hope for Renault ahead of their return to the sport as a constructor with the third quickest time and an impressive 126 laps.
Sebastian Vettel posted Ferrari's best time of testing so far on the medium compound in fourth, whilst the Italian giants also ironed out a few reliability problems from Tuesday to post 151 laps.
There was also encouragement for McLaren-Honda as Jenson Button enjoyed a relatively trouble-free day with 121 laps.
However, Button's best time on soft tyres was 1.5 seconds down on Hamilton to again show the gulf the Woking-based team have to breach to get back to the front of the grid.
American newcomers Haas had their first nightmare day as a turbo charger problem meant Esteban Gutierrez failed to even register a lap time.
Once again matters on the track were overhshadowed by the ongoing discussions into rules changes for the upcoming season with the new knock-out form of qualifying agreed last week at the F1 commission coming under fire.
The idea remains to introduce more excitement to the sport after two years of domination by Hamilton.
Ferrari chief Sergio Marchionne called for more time for discuss the new qualifying format before it is introduced.
Meanwhile, FIA race director Charlie Whiting met with the drivers to discuss their concerns.