Sauber driver Felipe Nasr reckons he has made a step forwards after sampling a new chassis during practice for the Russian Grand Prix.
Nasr was unable to match team-mate Marcus Ericsson across the opening three Grands Prix and requested that Sauber bring a new chassis to Russia, a demand which the team met.
Nasr finished 14th in the opening session, with Ericsson in 19th, while the Brazilian was 19th in the second session as Ericsson brought up the rear of the pack, 0.9s behind his team-mate.
"I covered a decent mileage, which was important in order to understand how the tyres behave compared to last year," he said.
"The car is a lot more together compared to the previous race weekends.
"I was satisfied with the pace on Soft tyres, but we have to work more on the Super Soft compound."
Ericsson was understandably downbeat after a trying day of practice.
"We have tried different set-ups, but we are not going in the right direction yet," he said.
"We have to look into the data and see what we can make better for the rest of the weekend."