Nico Rosberg believes Mercedes has taken a step backward with its car's handling at Silverstone despite going fastest in Friday practice.
The German acknowledged that the car was quick, but said its balance in high-speed corners was disconcerting.
"We kind of went backward in the high-speed corners, which is not good, so we have to sort that out," Rosberg said. "The difficult thing is to understand what the cause is, so we have to do a lot of analysis now to try and sort it out.
"If you take some front wing out, then it helps that area but makes other areas worse and gives you understeer in the middle of the corners. You want to do something just in the entry to high speed corners, which for example is where the car is worst. It could be the diffuser isn't working properly.
"It's been a good day pace-wise, qualifying is looking good and that's a nice start to the weekend. We need to work out how to improve high-speed corners because it just affects that and not anywhere else. Long runs on this track are going to be the big challenge for us, to try and hold our qualifying position."
Rosberg's team-mate Lewis Hamilton was fifth fastest and also very unsettled.
"I can't remember the last time I felt so uncomfortable with the setup," Hamilton admitted. "We just need to go back and work on it to make it feel good."