Ahead of today's sole practice session, the air temperature is 25.5 degrees C, while the track temperature is 52.6 degrees. It is bright and sunny.

Valtteri Bottas led a Mercedes 1-2 yesterday, but the day was not without its problems as Lewis Hamilton suffered a misfire which cost him track-time after an off which saw him up before the stewards.

The Briton wasn't along in exploring the outer limits of the track, with all manner of drivers - including both the Bulls - either running wide or spinning at some point or another.

The big surprise of the day was the pace of the McLarens, with Lando Norris finishing ahead of Max Verstappen and Carlos Sainz ahead of Pierre Gasly.

Ferrari brought a number of upgrades which don't appear to have had the desired effect, while Honda and Renault have both brought a new spec engine.

Indeed, in the moments before the start of the session, it is revealed that Ferrari has switched to the old floor, but kept the new front wing.

Other than a lack of grip, the wind was causing problems and certainly played a part in a number of those spins.

As Pirelli pointed out, the remarkable thing about yesterday was the fact that Hamilton set his fastest time on the mediums, as opposed to everyone else who set their best time on the softs. This could mean some drivers qualifying on the yellow-banded rubber this afternoon and others opting to start the race on them.

The lights go green and the McLaren pair lead the way, followed by Grosjean, who was an unhappy man yesterday.

Albon and Magnussen head out, like the previous three runners they are on the softs.

Raikkonen is the first driver to head out on mediums, while, eight minutes in, Kubica is the first driver to post a time (35.832). Moments later Kvyat posts 33.398.

As the Renault pair head out, Kvyat improves to 32.744, while Kubica gets down to 35.345.

Fourteen minutes in and Hulkenberg is the third driver to post a time, the German crossing the line at 33.720.

A 32.690 sees Ricciardo go quickest on the softs, as Gasly is the first of the big guns to head out. Teammate Hulkenberg responds with a 32.417.

Gasly goes third with a 32.679, just moments after Norris went second with a 32.446.

Twenty minutes in and Bottas is first of the really big guns to post a time, the Finn stopping the clock at 31.383.

"Something's not right, no power," reports Russell, who is told to pit. "Can I change gears," he asks.

Hamilton goes second with a 31.700, but all eyes are on Leclerc who is quickest in the first two sectors, finally crossing the line at 31.446, the Ferrari losing its time in the final, twisty sector.

Vettel goes fourth with a 31.743 as Sainz can only manage 11th.

As Verstappen heads out, Vettel improves to third (31.542), as teammate Leclerc posts 31.118 to go quickest.

Verstappen's first flying lap sees the Dutchman go fifth with a 31.933, albeit 0.813s off Leclerc's pace. Teammate Gasly remains ninth (32.616).

Hamilton takes the top spot with a 31.108, as Bottas begins another hot lap. The Finn subsequently responding with a 30.853.

At half-time, it's: Bottas, Hamilton, Leclerc, Vettel, Verstappen, Hulkenberg, Norris, Sainz, Albon and Gasly.

"I have no grip at the rear," reports Verstappen, one of a number of drivers to make a mistake as the pressure ramps up.

As attention turns to qualifying sims, Ricciardo goes sixth with a 32.321, despite a very scrappy lap, albeit on 6-lap old rubber.

In the Ferrari garage, mechanics are working on an issue with Vettel's seatbelt.

"Impossible to do the burnout," reports Giovinazzi.

Back on track, Russell is once again claiming "no power". Again, he is told to pit.

Bottas heads out on fresh rubber, and unsurprisingly he is quickest in the opening sectors. He finally crosses the line at 30.159, which is marginally off last year's pole.

He's come out earlier than expected, but this is most likely so that he (and Hamilton) can also try the mediums ahead of this afternoon's session.

Bottas is told that there is still room for improvement in T8.

Hamilton can only manage a PB is S1, and as a result of a mistake opts to abort the lap. Elsewhere, Bottas has gone wide on his cool-down lap.

Next time around, Hamilton goes quickest in S2, despite a poor opening sector. At the line he posts 30.200, 0.041s down on his teammate.

Leclerc improves to 30.605, but remains 0.446s off the pace, while Vettel can only manage 30.810.

While the Bulls consolidate fifth and sixth, albeit both over a second off the pace, Vettel goes quickest in S2. However, a poor sector means he remains fourth (30.633).

Leclerc now goes quickest in S1, as Raikkonen and Giovinazzi go eighth and ninth overall. A mistake in S2 costs Leclerc dearly, the youngster failing to improve his overall time.

Norris goes seventh with a 31.654, ahead of Sainz, Raikkonen and Giovinazzi as Verstappen complains that he has "absolutely no grip, everywhere, understeer, oversteer".

Both Racing Points at the foot of the timesheets along with the Williams pair. The Haas duo are also both over 2.2s off the pace.

Ricciardo improves to 8th with a 31.802 as teammate Hulkenberg posts 32.023 to go 11th.

The session ends. Bottas is quickest, ahead of Hamilton, Leclerc, Vettel, Verstappen, Gasly, Norris, Ricciardo, Sainz and Raikkonen.

Hulkenberg is eleventh, ahead of Giovinazzi, Albon, Grosjean, Magnussen, Perez, Kvyat, Stroll, Kubica and Russell.

While it's looking good for Mercedes (again), The Bulls look to be under pressure from both McLaren and Renault.

Check out our Saturday gallery from Le Castellet, here.