SAKHIR, Bahrain -- Charles Leclerc set the fastest time on the opening morning of the second test in Bahrain as Ferrari continued its strong preseason form.
The three-day test in Bahrain is the final chance for teams to run their cars ahead of the first race next weekend at the same circuit.
Reigning constructors' champions Mercedes generated headlines the moment its car left the garage thanks to an upgraded engine cover and sidepod layout.
The updated W13 is arguably the most extreme interpretation of F1's new regulations, which are designed to improve the chances of overtaking.
The new sidepods on the Mercedes feature very small air inlets either side of the cockpit and a sloping engine cover that appears to exist separately from the upper side-impact crash structure on which the wing mirrors are mounted. It also features two sets of louvres cut into each sidepod to help with cooling.
Despite the radical design, Lewis Hamilton seemed to struggle for much of the morning with the car porpoising on the straights. Porpoising was a problem for all teams at the opening test in Barcelona and results in the car bouncing up and down on its suspension at high speed due to the intermittent stalling of the car's underfloor aerodynamics.
At one stage, Hamilton's car was trailed by showers of sparks on the pit straight and he struggled to get the W13 slowed down in the braking zones at Turn 1 and Turn 10. One solution to the porpoising problem is to run the car at a higher ride height, but teams will be keen to find a solution as running a higher ride height also results in a loss of aerodynamic performance.
Hamilton set the fifth fastest time of the morning session with a lap 1.8s off Leclerc. Alex Albon in the Williams , Sebastian Vettel in the Aston Martin and Sergio Perez in the Red Bull filled the gap between the Ferrari at the top of the timescreens and Hamilton.
Haas was the only team that did not take part in the morning session. The team's freight was delayed on the way to Bahrain, meaning it did not have enough time to get the car ready for the start of the test.
However, ESPN understands Haas will get four hours of running back as the freight delay was a result of a delay from one of Formula One's cargo planes. The original plan was to run on Sunday, but that has been amended to allowing Haas to run longer after each day of testing as running on Sunday would have been a breach of the rules that preseason testing has to take place over three consecutive days.
1. Charles Leclerc - Ferrari - 1:34.531 - 64 laps
2. Alexander Albon - Williams - 1:35.070 - 53 laps
3. Sebastian Vettel - Aston Martin - 1:35.706 - 39 laps
4. Sergio Perez - Red Bull - 1:35.977 - 70 laps
5. Lewis Hamilton - Mercedes - 1:36.365 - 62 laps
6. Esteban Ocon - Alpine - 1:36.768 - 42 laps
7. Guanyu Zhou - Alfa Romeo - 1:37.164 - 54 laps
8. Lando Norris - McLaren - 1:37.580 - 21 laps
9. Pierre Gasly - AlphaTauri - 1:37.888 - 44 laps
Thursday's test will resume with four hours after the lunch break, before eight hours each on Friday and Saturday.
This week's test is the final track action for the team's ahead of the Bahrain Grand Prix on March 20.