Mercedes hints at progress with tyre weakness

Valtteri Bottas takes over from Lewis Hamilton for Wednesday's running, after the Briton spent day one focusing on some new parts evaluation and tyre runs.

Mercedes is adamant that unlocking stronger pace in the race is key to it beating Ferrari, and Hamilton felt progress had been made on the opening day.

"Our focus was on advancing our understanding of the tyres and also the rear of the car so that we can improve our long runs - particularly during the race and on the super-soft compound," said Hamilton after his test came to an end.

"We came here with a specific goal, so it was positive to get on top of that with the team."

World championship leader Sebastian Vettel will return to normal testing duties for Ferrari on Wednesday, having spent Tuesday working on Pirelli's 2018 evaluation project.

Ferrari's challenge is slightly different from Mercedes, in that Vettel's team is on top of its race performance but has proved lacking on single-lap pace.

The team may well choose to concentrate on that because, with overtaking more difficult in 2017, not being able to control the race from the front is a disadvantage.

Pierre Gasly is taking over for Red Bull, with Daniel Ricciardo's running on Tuesday having been cut short by an engine failure.

Force India will split running between Esteban Ocon and Sergio Perez as it continues work on evaluation of new parts, while Kevin Magnussen will be tasked with further work on Haas's brakes.

His team-mate Romain Grosjean, who has had strongly critical of current supplier Brembo, was encouraged by the work he did with alternative products from Carbone Industries on Tuesday.

"We still have a lot of work to do around them and see the performance, but it feels better, as it was last year," explained Grosjean on Tuesday evening.

"Otherwise it's quite similar. We just need to see if we can actually make it work with all our mapping."

When asked if he was positive enough for a switch to come in time for the next race, Grosjean said: "I think it could come for Russia. It's all ready.

"But only if we're confident that we're going to start Russia without a hitch, as you cannot miss FP1 and part of FP2 because you're not right on mapping."

McLaren will also be hoping for a better day than Tuesday, when an engine change prompted by an ERS water leak cost it hours of running and left it behind in its test programme.

Stoffel Vandoorne is taking over from Oliver Turvey for day two.