Barcelona, Spain - Valtteri Bottas lapped Barcelona's Circuit de Catalunya faster than any driver in the V6 turbo era on Wednesday as Formula One champion Mercedes enjoyed another trouble-free day of pre-season testing.
Bottas, whose retired predecessor and 2016 world champion Nico Rosberg paid a flying visit during the sunny morning session, completed 75 laps with a best time of 1m19.705s on ultra-soft tyres - a significant step up from the 1m20.960s set by Ferrari's Kimi Raikkonen on soft tyres on Tuesday, which had ranked as the fastest of the opening 2017 test.
It also offered further evidence of how much quicker the new, wider cars are with their more aggressive aerodynamics and fatter tyres. The fastest time in 2016 Barcelona testing was 1m22.765s.
Bottas's time would have put his car on pole position for every race at the Spanish circuit since 2007, when the layout was changed.
"We completed lots of mileage and the entire programme that we'd planned to do – including some long and short runs, collecting information on the different tyre compounds," said Bottas.
"It was a pretty straightforward day again, so I think everyone has done a great job so far. The car is running well and it's feeling better and better."
Ferrari fuel run
The Finn handed over to team-mate Lewis Hamilton for the afternoon, with the triple world champion completing a further 95 laps.
Ferrari's Sebastian Vettel completed more than a race distance before lunchtime, doing 69 laps on medium tyres, and ended the day with a tally of 139.
His car stopped on track near the end of the session, and was pushed down pit lane, but it looked as if Ferrari was doing a fuel run to see how far it would go on a full tank.
Australian Daniel Ricciardo was third fastest for Red Bull, completing 70 laps in all. Renault's Jolyon Palmer – who had an early spin into the gravel that brought out red flags - was fourth with a best lap set on softs.
Canadian rookie Lance Stroll got back into the Williams after an early spin on Tuesday damaged the car and ended his first day of testing, completing 98 laps.
The 18-year-old returned to the gravel, however, and finished in the tyre wall, bringing out more red flags, in a sign that he still has plenty to learn.
Williams had to end the session early for the second day in a row with its participation on Thursday in doubt.
Honda-powered McLaren picked up the pace, with double world champion Fernando Alonso managing 72 laps. The team said its main focus was gathering data.
Toro Rosso and Haas both spent long spells in the garage, with the former's Spanish driver Carlos Sainz doing just one installation lap in the morning.