Mercedes' ominous warning for rivals at Barcelona test

Lotus driver Romain Grosjean set the fastest time of the second Formula 1 pre-season test, but Mercedes cast a shadow over all rivals at Barcelona.

Grosjean used Pirelli's super-soft tyres on Sunday to make it three out of four days on top for the team, after team-mate Pastor Maldonado went quickest on Thursday and Saturday in the new E23.

Despite Lotus's new-found pace with its latest car and switch from Renault to Mercedes power, and Daniel Ricciardo topping day two for Red Bull, it was last year's dominant force that made the biggest impression at Barcelona.

Nico Rosberg did not use either of the two softer-compound Pirellis on Sunday, but with medium rubber on the W06 the 2014 runner-up set the second fastest time of the week, just a quarter of a second behind Grosjean's best on tyres that are 1.5s-2s faster.

That followed an ominous race simulation from world champion Lewis Hamilton on Friday, during which he was comfortably faster than Ricciardo's Red Bull, despite again being on slower rubber and running longer on his stint.

Such a positive result for Mercedes looked in doubt after Thursday, when reserve driver Pascal Wehrlein had to be recalled from Force India in the afternoon duo to Hamilton falling ill with a fever and a neck issue stopping Rosberg from taking over.

Despite the setback the W06 completed more mileage than any other car at the test, racking up 446 laps (or 1290 miles).

The Renault-powered Red Bull and Toro Rosso were next-best on the mileage count, both within 50 laps of Mercedes' tally, and Ricciardo topped Friday with the best soft-tyred time of the week.

The Aussie narrowly outpaced Kimi Raikkonen's Ferrari and Felipe Massa's Williams on day two, and he was 0.4s faster than team-mate Daniil Kvyat managed on Sunday.

It was a much-improved turnover of laps for the four-time champion team, but the same could not be said for McLaren-Honda, which had a dismal test that was constantly thwarted by MGU-K seal issues.

Fernando Alonso and Jenson Button completed just 124 laps between them with almost half of that tally achieved on Saturday.

Both drivers were unable to string a significant number of laps together, and Button managed just 45 in total.

A disastrous week was compounded when Alonso suffered concussion in a crash on the final morning that required an overnight hospital stay and stopped Button taking over in the afternoon as planned.

With Mercedes not using the softer tyres and Williams opting to keep clear of performance runs as well, save for Massa's soft-tyre effort on Friday, laptimes were not a clear indicator of the pecking order.

Raikkonen gave further encouragement that Ferrari's SF15-T will move it closer to the front of the grid by shadowing Ricciardo on Friday, 0.010s behind.

But the Scuderia lost time on Sunday with what Sebastian Vettel called "teething problems".

Elsewhere, Force India's Sergio Perez and Toro Rosso's Max Verstappen used super-soft tyres to set the seventh and eighth best times of the week, but both teams were compromised on the final day.

Nico Hulkenberg's Force India detonated its Mercedes engine, while Carlos Sainz Jr crashed at Turn 3 in the Toro Rosso.