Zhou Guanyu has suggested that the Alfa Romeo Sauber F1 team has made “massive gains” with its 2023 C43 F1 car.

The Chinese driver topped pre-season testing in Bahrain on Friday, heading Red Bull’s Max Verstappen by 0.04s at the end of more than eight hours of running.

It’s a promising start for Alfa Romeo Sauber which last year climbed to sixth in the constructors’ championship.

That was despite the team’s fortunes flagging in the second half of the competition as rivals outpaced it in terms of development.

“We knew the main focus points throughout the second half of the season [in 2022], that we need to get the car back in shape for the early stages this year,” Zhou said.

“Seems to be the car is handling nice, particularly in the high-speed, compared to last year.

“So I’m happy that the step, the development over the winter, has been proved as correct.”

On Friday, Zhou spent time assessing the softer end of Pirelli’s range of tyres for Alfa Romeo Sauber before completing a race simulation in the afternoon.

The information gleaned from those runs, and what came out of Thursday’s running, leaves Zhou optimistic for the opening races of the campaign.

“It gives drivers confidence, gives us the ability to push more into the high-speed corners,” he said when asked about the car’s more stable rear end.

“I’m excited for this week, next weekend, and also especially for Jeddah to see because it could be quite good.

“It’s too early to say the performance against the others, but at least it’s a massive gain in terms of the step we were able to make with the new regulations as well.”

Rules for 2023 remained largely stable, aside from the tweaks to the height of the floor and throat of the diffuser.

Those changes are estimated to have cost about half a second worth of performance.

Zhou’s Friday time, however, was 1.6 seconds faster than the same session in testing last year – and was good enough to see him seventh on the grid for last year’s Bahrain Grand Prix.

Valtteri Bottas has taken over the running for the balance of the test, the Finn to complete both of Saturday’s sessions as pre-season draws to a close in Bahrain.