Ahead of today's sole practice session the air temperature is 30 degrees C, while the track temperature is 42 degrees. It is bright and sunny.

Having introduced their various upgrades yesterday, today is when the teams decide whether to stick or twist as the cars have to be fine-tuned before qualifying.

Their upgrade dilemma aside, it was a busy night for Ferrari, McLaren and Williams, as they were all forced to break the curfew.

A fuel system issue mean that Ferrari had to change Carlos Sainz' chassis, while floor damage incurred on Friday meant a chassis change for Lando Norris also. Meanwhile, following his engine failure yesterday Alfa Romeo has changed the engine in Valtteri Bottas' car.

The failure happened early in FP2 which meant the Finn has done no running on the softs and also missed out on testing the various upgrades the team has brought here.

While Charles Leclerc set the pace in both session, the Ferrari driver insists that he is not entirely convinced he has this one in the bag, admitting concern over race pace, while Max Verstappen, who finished fifth, appears quietly confident.

Also looking confident are the Mercedes pair, but then we said that heading into FP3 in Miami and we all know how that went.

Alpine is looking strong this weekend, as are Aston Martin, while due to its various issues McLaren has yet to show its hand. Talking of the Woking outfit, today both cars have the full upgrade package.

Haas, the only team not to bring any upgrades, will be happy to have ended the first day 10th (Schumacher) and 12th (Magnussen).

The lights go green and Norris leads the way, followed by teammate Ricciardo, Gasly and Stroll. The Briton is on softs while the other three are on hards.

Norris crosses the line at 23.641 to get the session underway, as Gasly pits with smoke billowing from the rear of the car. "Get ready to jump out," he was warned as he headed into the pitlane.

Bottas, who, like Norris, has to make up for lost time, posts a 21.326 to go top.

Schumacher goes third (25.467) and Tsunoda fourth (25.663), but both are demoted by Magnussen (22.829) - the Dane benefiting from a tow from Bottas.

11 minutes in and only 9 drivers have appeared thus far, with only five of them posting a time.

A huge roar greets Alonso as he heads out on softs.

"Rear brakes are burning, rear-right," warns Schumacher as he heads into the pitlane, the on-board camera revealing the damage as flames leap from the offending corner of the car.

Meanwhile, Alonso goes second with a 21.775, 0.449s down on Bottas' best.

On softs, Sainz goes quickest in the first two sectors, maintaining the pace in S3 he crosses the line at 20.484.

However, teammate Leclerc is on track and immediately goes quickest in the opening sector. The world championship leader subsequently goes quickest with a 20.278.

As the Mercedes pair head out, followed by Perez, Verstappen remains the only 'no show'.

Ocon goes fourth and Zhou sixth, ahead of Albon, Ricciardo and Magnussen.

Russell's first flying lap sees the Briton go third with a 21.129, while Hamilton can only manage sixth (21.500) due to a DRS issue.

A 21.518 sees Perez go seventh.

Sainz goes quickest in the opening sector, but is unable to maintain the pace for the rest of the lap.

Twenty-four minutes in Verstappen finally heads down the pitlane on fresh softs.

AlphaTauri reveals that Gasly's pyrotechnics were down to a faulty heat shield. Unfortunately this means the Frenchman is out of the session.

Verstappen goes quickest in S1, but is only able to manage a PB in S2. At the line it's 20.475 as he goes second, 0.197s down on Leclerc, the Red Bull losing out in the middle sector.

"No," is the first response from Leclerc when he is asked if he wants to do another push lap.

A strong opening sector for Hamilton is followed by a poor second, nonetheless another strong sector at the end sees the Briton improve to sixth with a 21.170.

"The car doesn't turn at low speed," says Verstappen, "it's terrible, the last chicane as well."

PBs in all three sectors see Magnussen improve to fifth with a 20.646.

While Sainz posts a PB in S2, Leclerc goes purple. The Spaniard crosses the line at 20.129 to go top, but moments later his teammate stops the clock at 19.772.

"I only want to know the fastest," snaps Hamilton when told where he is losing out to his teammate.

On fresh softs, Russell goes quickest in S1 as Bottas goes sixth overall (20.781). Having posted a PB in S2, Russell subsequently crosses the line at 19.920 to go second, just 0.148s down on Leclerc.

The Aston Martin pair finally head out on softs, leaving the McLaren duo as the only drivers yet to try the red-banded rubber. Hamilton heads out on fresh softs.

Alonso is unable to improve on 13th (21.572). Indeed, he is demoted when Stroll posts a 21.520 to go 12th and Vettel goes ninth with a 20.944.

Currently sixth, Magnussen heads out on mediums as Verstappen bolts on his second set of softs.

A PB in S1 is followed by another in S2, as Perez also looks set to improve. At the line it's a 19.844 for the Dutchman, who goes second, while Perez can only mange sixth (20.260).

In the meantime, Hamilton had improves to fourth with a 20.002.

The top six - Leclerc, Verstappen, Russell, Hamilton, Sainz and Perez - are covered by 0.488s.

With six minutes remaining, Norris and Tsunoda head out on softs for the first time.

The Briton goes seventh with a 20.403, while the Japanese crosses the line at 21.449 to go 13th.

Alonso improves to 13th with a 20.981, while, on his first run on the softs, Ricciardo improves to 11th with a 20.910.

The session ends. Leclerc is quickest, ahead of Verstappen, Russell, Hamilton, Sainz, Perez, Norris, Magnussen, Bottas and Ocon.

Ricciardo is eleventh, ahead of Vettel, Alonso, Zhou, Tsunoda, Stroll, Albon, Latifi, Schumacher and Gasly.

So it's basically Ferrari, Red Bull and Mercedes with one representative from McLaren, Haas, Alfa Romeo and Alpine making up the leading ten.

Unlike Miami, Mercedes appears to have carried its Friday pace through, though it remains to be seen how the German team fares once Ferrari and Red Bull up the ante.

Certainly, Ferrari appears to have the edge but one cannot help but notice that Verstappen appears remarkably calm, the Dutchman no doubt aware of the Italian team's fears over its race pace and also tyre deg.

On to qualifying.

Check out our Saturday gallery from Barcelona, here.