Having topped morning practice in Monaco on Thursday, Lewis Hamilton was shocked by how differently things felt after lunch.
“It was handling really good this morning," Hamilton said. "FP1 was really good, the car was feeling great.
"But this afternoon, for whatever reasons, the tyres weren’t working," he continued. "There was night and day difference, black and white.
"We couldn’t work the tyres for some reason. There was lots of sliding about.
"That’s something we have to study and fix for Saturday," he added. "Lot of studying to do to find out where we went wrong, but I’m confident in my guys."
At least Monaco's unusual schedule - with practice taking place on Thursday, and Friday officially a 'rest day' for the teams - works in Mercedes' favour.
"We have two days to work on the car," Hamilton agreed. "It gives the guys here more time to work on the car. It's spread over two days, rather than everything tonight."
Even if the team does get on top of its set-up issues, effectively losing a session of practice puts them on the back foot to their rivals this weekend.
"Ferrari are very quick again and Red Bull are also looking good this weekend," Hamilton acknowledged. "We're looking forward to a real fight on Saturday."
Hamilton had been relieved to find that the new 2017 aerodynamic and tyre regulations hadn't had an adverse effect on racing at Monaco.
It was feared that the wider cars might be more difficult to thread their way around the narrow streets of Monaco. But Hamilton felt that if anything, the new cars were actually better suited to the venue.
“You get used to it real quick," he said. "It’s like you driving a normal car and then driving an SUV. You get used to it.
“It’s the same as before. The car is a lot better, it’s got more grip. If anything, it might be easier. It feels great.
"Monaco is always amazing to drive, and it’s definitely the best car I’ve driven round here."
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Gallery: All the pictures from Thursday in Monaco
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