Max Verstappen says Toro Rosso has work to do in order to cure the oversteer affecting his STR11, following Friday's practice sessions for the Russian Grand Prix.
Verstappen was 15th in the opening session but improved to place 12th in second practice, marginally behind team-mate Carlos Sainz Jr.
"It was quite a difficult start to the weekend," he said. "I experienced a lot of oversteer and we haven’t found the right solution for this yet.
"It felt very tricky out there today – it’s difficult to enter the corner in the right way because when you try to go a bit faster you easily end up off track.
"Fortunately though, it’s only Friday, so we still have some time to work on this – it will be a long night but I’m confident we will be ready for tomorrow."
Sainz Jr. was more upbeat regarding the handling of his STR11.
"We were able to cover all of our run plan with no issues, so I’m happy with that," he said.
"I’m pleased with the car so far and I’m looking forward to the rest of the weekend. As we’ve seen during the first three races, the midfield is extremely tight so we need to keep working because it’s not going to be easy."