Lewis Hamilton declared himself extremely uncomfortable with the Mercedes set-up at the end of free practice for the British Grand Prix.
With the Silverstone crowd expecting Hamilton to be the strongest of the home drivers on present form, he had been hoping for a big weekend, but ending Friday disappointed.
"I can't remember the last time I felt so uncomfortable with the set-up," Hamilton admitted.
"We just need to go back and work on it to make it feel good."
The Briton was fifth fastest, while his team-mate Nico Rosberg set the pace.
But Rosberg also had concerns about the car's handling.
The German acknowledged that the car was quick, but said its balance in high-speed corners was disconcerting.
"We kind of went backwards into 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."
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