Carlos Sainz has explained why he still feels "a bit lost" in the cockpit of the Williams FW47, his car for the 2025 F1 season.

The Spanish driver made the switch from Ferrari to the Grove-based squad over the winter and headlined the second day of pre-season testing at the Bahrain International Circuit, finishing top after a full day of running.

However, the extensive milage under his belt on that middle day may have created an illusion, because the 30-year-old has professed to still being somewhat at odds with the machine beneath him, despite 127 more laps behind the wheel.

"In terms of driving style, I'm still understanding what I need to do with this car to go quick, because, if I'm honest, I'm still a bit lost as to where to find the lap time," Sainz told F1TV.

"I don't know if it's gonna come on entries, it's gonna come on exits, minimum speeds."

Nonetheless, he was quick to point out how critical that extended running was for him to better understand the intricacies of the FW47, even if it did produce a potentially inaccurate reading at this stage of the year.

"And that's why [that] run was important for me to understand where the lap time is coming from," the four-time grand prix winner said.

"I feel like when I push it, I can get to a decent level, but I still don't know where the last two tenths of the car are."

Although he had to hand over the car to team-mate Alex Albon for the final day in Bahrain, the form shown by Sainz has set tails wagging up and down the paddock.

Andrea Stella, team principal of his former team McLaren, believes Williams could be knocking on the door of the top four.

Either way, the final bit of extra performance Sainz feels is still lacking is what he will be hunting for over the opening rounds of the campaign.

"This is what I will need to discover during the first five, six races, as I put more soft tyres on the car, to try and understand where this is: where's the lap time gonna come from in this car."