Valtteri Bottas posts fastest time of the week as Mercedes begins to show its hand.

While there is one day remaining of this week's opening pre-season test, the teams are under pressure today because tomorrow - the weather gods having been kind so far this week - is set aside for wet testing.

Consequently, it is vital that the teams get as much (dry) running in today as possible.

It goes without saying that Mercedes had another trouble-free morning, Valtteri Bottas completing 75 laps without missing a beat.

Along the way the Finn also managed to post two sub 1:19s laps - his best being 1:19.705 - quicker than anything we've seen this week.

That said, like teammate Lewis Hamilton yesterday, the Finn was on the purple-banded ultrasofts when he posted his best time.

Red Bull continues to improve, Daniel Ricciardo completing 48 laps on his way to posting the second best time of the morning, a 21.153 on softs.

In a change to the Austrian team's programme, Max Verstappen will drive this afternoon - one of several changes as the teams anticipate tomorrow's wet running.

Despite causing the morning's sole red flag when he headed off into the gravel on his out lap, Jolyon Palmer ended the morning third on the timesheets despite missing the first two hours of running following that off.

This afternoon the Briton hands over to teammate Nico Hulkenberg.

A quiet morning for Sebastian Vettel, the German completing 69 laps on his way to posting the fourth best time and never venturing from the medium tyres, just like Monday. Indeed, according to the team, from 10:30 it was used mediums only.

Following yesterday's off which resulted in Williams having to bring its day to an early close, the Grove outfit changed its schedule and had Lance Stroll back in the car.

The Canadian was one of several drivers who didn't post a time until two hours into the session, indeed, for the first fifteen minutes the FW40 remained in its garage - behind the screens - engine running.

Talking of screens, Red Bull is as paranoid as ever, the Milton Keynes crew doing its level best to shield the RB13 from prying eyes at every opportunity... if there was a way of running the car behind a screen on track we're sure they'd do it.

Stroll gradually got to grips with the car and by lunch was up to sixth. However, over enthusiasm, or perhaps lack of confidence, saw the Canadian head off into the gravel just as the chequered flag was being waved. It remains to be seen whether the FW40 has sustained more damage.

A promising morning for Sauber with Marcus Ericsson finishing fifth on the timesheets, albeit 2.119s off the pace.

A good workmanlike performance from Alfonso Celis, the Force India reserve quietly going about his job and putting another 39 laps on the car with no dramas.

With just the two cars on track at the time, when the red flag went up following Palmer's off, many (wrongly) assumed that Fernando Alonso was the culprit/victim. Not so.

Though, once again, the car has spent more time in the garage than anyone would wish, the Spaniard has completed 28 laps - just one less than all Monday's running - and is eighth on the sheets.

Much of the early part of the morning appeared to be about data, or perhaps correlation, as the Spaniard completed a series of single laps. Indeed, like several others, we were two hours into the session before the two-time world champion posted a time.

Like McLaren, Toro Rosso spent more time in the garage that anyone would have wished, and though Daniil Kvyat was one of the first out this morning, he no doubt expected to have more than 31 laps on the board.

After the high of yesterday, when Kevin Magnussen was fourth quickest, it was back to earth with a bump for Haas today.

Having waited two hours before he finally posted a time, the Frenchman then returned to the pits where the Renault remained for another hour.

By the time the chequered flag was being waved for lunch the Frenchman had completed 27 laps.

A welcome sight in the garage this morning was Nico Rosberg, the world champion visiting his old pals at Mercedes - at least some of them - and clearly enjoying watching the action as a spectator.

Check out our Wednesday gallery from Barcelona, here.