Romain Grosjean will once again revert back to the Australia-spec Haas for the Russian Grand Prix.

Unhappy with the performance of the team's upgrades, the Frenchman first made the change back at Silverstone and continued until the Hungarian Grand Prix with mixed results.

At the past three races though, both he and teammate Kevin Magnussen have used the latest spec VF-19 due to low downforce limitations at Spa and Monza and to assess the high downforce performance in Singapore.

Now though, Haas will once again split their drivers as part of their efforts to find solutions for next year's Haas car.

“Obviously, all this work is brought forward to next year because next year’s car will be an evolution, as there’s no regulation change," team boss Guenther Steiner explained.

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"This year it was a new regulation, so whatever we learn on this car we can implement on next year’s car, that was our aim from halfway through the season when we realized we were struggling with our car.

"We want to make sure not to make the same mistakes on next year’s car – that was our main aim from midway through this season.”

At the start of the year, Haas was the dominant midfield team but problems with the tyres and race pace were often blamed for their lack of results.

Now though Grosjean admits developing this year's design has proven the most difficult task.

“We’ve brought updates during the year on the car and those updates haven’t really been working as expected," he said.

"So, we’re really trying to understand where the correlation from the wind tunnel to the track is.

"That’s why we’re going to try a different setup, a different aero package on the car, and see if we can actually get a clear understanding and prepare as good as we can for 2020.”

Romain, who was recently confirmed on a new contract for next season, also noted how Sochi was the perfect track for analysing Haas' weaknesses.

“We need to understand why the new package wasn’t giving us the rear downforce that we want and expect," he said.

"Sochi is a difficult circuit to generate tire temperature, so if we get the rear downforce, then we should be able to generate the temperatures.

"Also, the consistency through the corner on a low-grip circuit is very important. If we get to that point, where we get the consistency from the chassis and the aerodynamics and the downforce to generate the grip with the tires, that’s what you want to get in Sochi.

"That’s what we’re going to try to do.”