Lewis Hamilton said Monaco this year is the "bumpiest" track he has ever driven on.
Hamilton finished 12th after second practice on Friday and was 0.9 seconds behind Ferrari's Charles Leclerc who topped the timesheets.
The seven-time world champion believes the issue he was having with his Mercedes car was not the same as the high-frequency aerodynamic problem which was fixed in time for the Spanish Grand Prix last weekend.
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"There are, like, 100 bumps on just one straight," Hamilton said afterwards.
"I don't know whether the others are experiencing the same as us. But it's the bumpiest rollercoaster ride.
"It's the bumpiest the track's ever been. It's probably the bumpiest track I've ever driven.
"That makes it difficult but in general our car bounces a lot. It's different bouncing to what we've experienced in the past because it's in the low speed [corners] also, but it's not aero. The bumps are making it worse.
"Putting a lap together is, wow, whole new ground. I don't remember experiencing that before.
"The grip doesn't feel terrible but it's just eyeballs coming out of the sockets. As anticipated, I didn't think we would be as quick as the Ferraris and Red Bulls. Our battle is to try and stay ahead of the McLarens."
Hamilton's Mercedes teammate George Russell, who came sixth, added: "The car is constantly smashing against the floor.
"We have experienced a lot of that this year but this is a very different philosophy and reasoning for the bouncing.
"There are sections where both tyres are off the ground - in Turn Five, the front right in the air, and it's so stiff the front left is popping up as well. You're almost doing a wheelie. We're doing everything we can to make it easier for us. It was a relatively good day but we are not where we want to be.
"We want to be best of the rest. That is a fair result this weekend behind Ferrari and Red Bull but we want to make sure we don't have cheeky little Lando popping it in there too."
Monegasque driver Leclerc was pleased with his overall result.
"For now we are competitive, so I'm happy," he said.
"The car looks strong. Also in the race pace we look good. The initial feeling is good so hopefully we can do the step we want for tomorrow and have a great weekend after that.
"But I really think we need to do another step for tomorrow because everyone has quite a bit of a margin on Friday so it is a bit the unknown."
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