Valtteri Bottas leads the way for Mercedes in Barcelona

Mercedes have been the class of the field this week and they reigned supreme once more on Wednesday after completing more laps than any other team

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Valtteri Bottas ended the penultimate day of testing leading the way for Mercedes as rookie teenager Lance Stroll crashed out for the second consecutive day in Barcelona.

Mercedes have been the class of the field this week and they reigned supreme once more on Wednesday after completing more laps than any other team.

Bottas, the 27-year-old Finnish driver whose time on the track was overseen by the man he replaced at Mercedes Nico Rosberg following his short visit to the paddock, also posted a time which would have been fast enough to be on pole position every year since 2007.

Bottas managed 75 laps before Lewis Hamilton roared into action after the lunch break to complete 95 tours of the Circuit de Catalunya.

For the third day in succession the reigning world champions were ahead of their rivals in mileage and Bottas' super-quick time proved they have the pace to match as they bid for a fourth drivers' and constructors' championship.

Stroll, the 18-year-old Canadian who has replaced Bottas at Williams this year, was the centre of more unwanted attention.

Just 24 hours after his first meaningful running behind the wheel of a Formula One car lasted just 12 laps following a spin, Stroll was in the wars again.

First, he lost control of his car moments before the lunch break and was stranded in the gravel. A pick-up truck was sent to collect him and his Williams.

Then in the afternoon he ended up in the tyre wall at turn six after he crashed and sustained significant damage to the front of his car which called an early halt to his day.

The session was suspended as the red-faced Canadian and his Williams were collected from the scene and taken on a pick-up truck back to the garage.

While Stroll completed nearly a century of laps his display is likely to be of concern to those at the British team.

Stroll was not the only driver to make a mistake. Jolyon Palmer's day got off the a troubled start after he lost control of his Renault at turn three and span into the gravel.

But the 26-year-old Briton returned to the track after a series of repairs to his car and delivered a decent haul of 51 laps.

While little can be read into lap times at this stage of the season, Palmer will still be pleased to occupy fourth in the standings as he hopes to build on the solitary point he scored in his debut year.

Bottas replaced Nico Rosberg at Mercedes (Getty)

McLaren have endured a difficult week in Barcelona with their hapless Honda engine suffering a host of reliability issues.

Double world champion Fernando Alonso was back in the car on Wednesday morning and managed to get 72 laps under his belt, but the Spaniard was nearly three seconds off Bottas.

Sebastian Vettel delivered another impressive show for Ferrari as he finished second in the order and completed a mammoth run of 139 laps - more than two race distances at this circuit - but his car stopped in the pit lane in the closing moments of the day and had to be wheeled back to his Ferrari garage.