Sauber drivers Nico Hulkenberg and Esteban Gutierrez concede that the team has a lot of work ahead of qualifying for the Bahrain Grand Prix.
Hulkenberg was fifteenth quickest in second practice, with Gutierrez down in eighteenth place.
"In terms of performance, there is still quite a lot of work for us to do," said Hulkenberg.
"I expected this circuit might highlight some of the weaknesses of the car, but I think there is some potential. I’m still not happy with the balance of the car, but I think we can find more performance tomorrow if we sort out the balance. We have a long night ahead of us to try and maximise everything for this weekend."
Gutierrez, who takes a five place penalty into qualifying, admits that a lack of stability and traction is hindering their progress.
"The first session was a bit tricky in terms of the balance of the car," said the Mexican.
"We were trying a lot of different settings and measurements, but everything came together this afternoon. However, we are still missing speed in the slow corners due to lack of stability and traction. We will look at the data and work on these characteristics so we can create a car with a better margin."