Bruno Senna believes Williams has to improve its consistency on slow corners following his first day of testing at Barcelona.
The Brazilian had another productive day in Spain on Tuesday, covering 97 laps on his way to the eighth fastest time of the session.
Senna said he was pleased with the car's handling over medium and high-speed corners, but he reckons there is still room for improvement on lower-speed ones.
"I think we are learning about it," said Senna at the end of the day. "Today I don't think we managed to improve as much as I think we need to. There is still room for improvement.
"Our car seems to be consistent on the medium and high-speed corners, but on the slow speed we still need to work."
Senna admitted he had run out of time to test solutions to try to solve the problem today.
"We'll have to wait and see if the changes we make are going to be enough to mitigate the issue that we have. I didn't have enough time today to try enough stuff to see."
Despite that, he was still pleased with his day's work after completing nearly 100 laps.
"We did a lot of laps today and again, reliability seems to be in a good place," he said. "The tyres are behaving differently here than they were in Jerez so we need to understand what we are doing, but overall we have learned a bit about the car."