Lewis Hamilton said he was left bemused by the "crazy" swings in his Mercedes W13 from circuit to circuit, after an inconclusive Friday's running at the Hungaroring.
The Briton ended both practice sessions seventh and 11th respectively, around one second adrift of the leading time on both occasions.
Mercedes' Trackside Engineering Director, Andrew Shovlin, acknowledged that some of the Silver Arrows' set-up experiments had not worked as planned, and Hamilton appeared to be feeling those effects.
"The car was a bit of a struggle today. It's crazy how it swings so much from track to track," Hamilton told Sky Sports F1.
"It's just set-up – trying to figure out how we can get the car working at the moment.
"It's a little bit loose and it's not doing what what we want it to do, so a difficult day."
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No major W13 updates for Hungary
With only one week since the last Grand Prix in France, Hamilton stated that the W13 was fundamentally the same version that he had driven to second place at the Circuit Paul Ricard.
"Nothing's changed on the car since last week. For some reason, this track is not working as well," said Hamilton.
"But I think, once we got it right, the gap [to the front] is about the same as last week, so around a second."
Hamilton lost downforce in FP2
Hamilton added that his Friday running had not been helped by floor damage sustained towards the end of FP2 that affected his W13's performance.
"I didn't get to run at the end because I sustained some damage on my floor, so I lost a lot of downforce, and after that, it was pretty tricky for the long run pace," he commented.
"It's going to be a tough weekend, that's for sure, but we'll give it everything."
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