Lewis Hamilton top in Spanish Grand Prix practice with upgraded Mercedes
Lewis Hamilton and Valtteri Bottas secured a Mercedes one-two in second practice at the Spanish Grand Prix, comfortably clear of the Ferraris.
Hamilton was 0.09 seconds quicker than his team-mate but 0.310secs clear of the Ferrari of Kimi Raikkonen, who was 0.118secs ahead of Sebastian Vettel.
Red Bull's Max Verstappen and Daniel Ricciardo were next, looking as if they have closed the gap to the top cars.
The top six were covered by less than 0.8secs, closer than so far this year.
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Mercedes also appeared to have an advantage during the race-simulation runs later in the session, lapping consistently quicker than the Ferraris throughout the long runs.
The Ferraris did seem to be able to lap as quickly as the Mercedes in race trim on occasional laps but could not keep the pace up.
All the teams have brought major aerodynamic upgrades to this race, but the one on the Mercedes is the most visually dramatic, with a new narrower nose and a number of other major changes. So far it appears to be having a significant effect.
Red Bull hoped their upgrade for this race would bring them closer to Mercedes and Ferrari and that, too, appears to be the case. Verstappen was just 0.6secs off the pace, with team-mate Ricciardo 0.1secs further adrift.
At the back of the field, it was a dismal day for home hero Fernando Alonso.
His McLaren-Honda broke down with a major engine failure on his first lap out of the pits in the first session, and he returned to his hotel to play tennis before that session was over.
Alonso was back at the track for the second session, but had to wait for nearly half an hour before he could get out on track while an engine change was completed.
When he did get out, he said the engine still felt down on power and he was slowest of all, 0.5secs slower than his nearest rival, and 1.4secs off the pace of team-mate Stoffel Vandoorne.
During first practice, Honda blamed the failure on an oil leak. Alonso said later: "The oil was coming out of a hole in the engine."
Alonso has failed to finish a race so far this season because of reliability problems, and he added: "It is not my career, my ability, my image. It is their career, their ability their money and their image, so I try to support the team and drive as fast as I can, but the problem is not entirely mine, it is much bigger for them."
Asked why he had left the track, he said he was trying to make up for training time lost because of his commuting back and forth to America to prepare for the Indy 500 after this race.
What they thought
Hamilton said after the session: "First practice was very, very good but in second practice the track changed and shifted quite a lot, so it was slippery and quite a lot slower for everyone - especially with the gusts of wind.
"It was massively challenging, but still fun nonetheless. The team has done an amazing job with the upgrades and the car is working just as we expected. It's been a much better start to the weekend for me than in Sochi, so I'm very happy."
Vettel said: "I'm not happy. Struggling a bit to find the rhythm, with the conditions, probably more myself than the car.
"I didn't get everything together but I can feel the car is quick so that's good. I am not worried. I am just not happy with how the day went. I wasn't always feeling as if I was captain on board.
"Sometimes somebody else was steering my ship but I hope tomorrow whoever that was will disappear."