Adrian Sutil has admitted that Sauber faces an uphill challenge ahead of this weekend's Chinese Grand Prix.
Sauber has yet to score a point in 2014 and Sutil is not expecting their fortunes to change drastically in China.
"The driveability of the car is still not easy," he said. "I am struggling with the tyres to get them to work. There is still a lot of work ahead of us.
"In comparison to Bahrain, I think we had more straight line top speed, which brings us closer to the teams in front of us. The mid-field is quite tight together. In terms of lap times, we are closer to our direct competitors, but we are obviously not there where we want to be."
Sutil's Sauber team-mate Esteban Gutierrez suffered a clutch issue before a problem with his Energy Recovery System hindered his progress. The Mexican nonetheless was able to return to the track later in the day.
"We did not have the full power and this issue effected the lap times enormously," he said. "However, we kept running to get a better feeling for the balance of the car. In the afternoon we were able to do the long runs. Obviously, we are not where we want to be at the moment."