By Alan Baldwin
BARCELONA (Reuters) - Valtteri Bottas lapped Barcelona's Circuit de Catalunya faster than any driver in the V6 turbo era on Wednesday as Formula One champions Mercedes enjoyed another trouble-free day of pre-season testing.
The Finn, 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 1 minute 19.705 seconds on ultra-soft tyres.
That was a significant step up from the 1:20.960 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 1:22.765. 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.
The 1.6-litre V6 power units were introduced in 2014.
"We completed lots of mileage and the entire program that we'd planned to do - including some long and short runs, collecting information on the different tire 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."
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 the pitlane, but it looked like Ferrari were 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 tire 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 their participation on Thursday in doubt.
Honda-powered McLaren picked up the pace, with double world champion Fernando Alonso managing 72 laps. The team said their 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.
(Editing by Ed Osmond)