Kamui Kobayashi says unusual track conditions on Thursday afternoon hindered Sauber's testing program on the penultimate day of the second test. The Japanese driver finished the day third fastest, 1.191sec down on Williams' Pastor Maldonado, after a late morning run on Pirelli's soft compound.
He said his program had centered more upon setup work, however, which the team had been unable to complete, despite totaling 99 laps, due to unusual conditions in the afternoon.
"The track was so strange in the afternoon," Kobayashi explained. "It seemed not to show performance and it was very difficult to compare lap times. I said to my engineer it seemed so strange.
"We have done a pretty good program already, and I think we can see the picture is not too bad. In the afternoon, though, we were surprised because lap times dropped a lot, which means we still have homework [for Friday].
"The priority is to check everything and get the data we missed [from yesterday]. Maybe if we have time after we can do a bit more performance wise, but the definite priority is to check and compare the data from yesterday, which was not stable, and improve the car."
Kobayashi said that testing conditions also made it difficult to compare Sauber's C31 to its rivals' efforts, but said the team had already made improvements from Jerez.
"We don't know if we could do anything different," he said when asked about Pastor Maldonado's Thursday benchmark. "We can't compare to others yet.
"It's not about the feeling of the car – I could say it is good, but if the lap time is three seconds slower then there is no chance. I believe the car is not too bad, but it is winter testing, so it's very difficult to say.
"We still have some work: in high-speed corners the balance is OK, but in low speed we have to find something. We've improved, though, definitely; we just need to do more setup work before we can see more performance."