BARCELONA, Spain (AP) Williams driver Valtteri Bottas topped preseason testing ahead of Mercedes driver Lewis Hamilton on Wednesday, although he was using faster tires than the two-time defending world champion.
Bottas, who was .361 seconds quicker than Hamilton, was on the super-soft option, while Hamilton used softs in slightly cooler morning conditions - again underlining how much Mercedes has in reserve in terms of speed.
Danish driver Kevin Magnussen was third fastest for Renault, while four-time champion Sebastian Vettel was fourth and completed a massive 151 laps on a good day for Ferrari, the day after Kimi Raikkonen had gear box problems.
Williams is showing excellent consistency, with Bottas having been second-fastest on Tuesday behind the other Mercedes of Nico Rosberg.
Rosberg was only ninth fastest this time, but the German driver was running a race simulation of the Spanish Grand Prix- which will be held here on May 15 - and so was primarily using slower medium tires.
Although Williams can take heart from another consistent showing from Bottas, his mark of 1 minute, 23.261 seconds was two hundredths slower than Rosberg's best time on Tuesday - which was also on soft tires.
Quite how much more Mercedes has to unleash in terms of speed remains to be seen. The team may prefer not to show it until March 20, when the new season gets underway at the Australian GP in Melbourne.
The pressure is clearly on everyone else to catch up.
On a warm and sunny day, drivers made the most of ideal racing conditions to complete a bewildering amount of laps, with seven of the 12 who went out completing 100 laps or more.
That neither Mercedes driver joined the 100 club - Rosberg did 91 laps and Hamilton 73 - matters little, for they already proved the car's reliability last week when amassing 675 laps between them in the first preseason test.
''What the team has done this year already for the miles we've done is super-motivating,'' Hamilton said. ''Every single person is going to hype us up. But you really don't know what fuel load Ferrari is on; they have a strong package. Even Williams looks like it has quite a strong package.''
Still, Mercedes head Toto Wolff is optimistic the W07 car could be even better than last year.
''The cars are more reliable, everybody is doing more laps,'' he said. ''I've the feeling it's the best season's start we've had in the last couple of years.''
Toro Rosso also has cause for confidence, after Spaniard Carlos Sainz led the day in terms of longevity with 166 laps to underline how reliable the car is.
Even McLaren, so troubled by engine troubles last year as it reverted back to Honda, enjoyed a stress-free day as veteran British driver Jenson Button posted 121 laps along with the fifth fastest time.
''This is obviously what we work for at McLaren, to have the best chassis,'' McLaren racing director Eric Boullier said. ''We're happy if we can achieve this; it means McLaren is back on track.''
There was only one red flag as Marcus Ericsson went off into the gravel on turn 4 and lost a wheel on his Sauber - although the Swedish driver still managed 55 laps.
The only team to have a truly bad day was newcomer Haas, as Mexican driver Esteban Gutierrez went out for one installation lap and came straight back in, due to a problem with the turbocharger.
French driver Romain Grosjean was scheduled to drive on Thursday and Friday but Gutierrez may now be given some extra time behind the wheel after managing only 23 laps on Tuesday before heading back to the garage with a fuel problem.