Lewis Hamilton says Mercedes has resumed its current struggles in hot weather, labelling his Friday Hungarian Grand Prix practice sessions as "not a good day" as the team seeks to find a solution.
Despite its recent success which has yielded two consecutive victories in Austria and at Silverstone, Mercedes expected to struggle in the hot conditions prevalent in the Hungarian summer; track temperatures in FP1 reached almost 60C in plus-30C ambient conditions.
Hamilton finished only 10th in FP1 and improved to seventh in second practice, while his team-mate George Russell managed fourth and fifth across the two Friday sessions.
This follows a pattern where the W15 has proven difficult to direct into the right set-up window amid hotter conditions and, although Hamilton reckoned the team had an inkling of what to change for FP3, he noted that the team had not "been on form" on Friday.
"Today's not been a good day, really. The weather's been good, and it's nice to be here, but we've not really been on form today," Hamilton explained.
"The car hasn't felt good set-up-wise, but I think we have an idea why and we'll just work overnight, but not the best prep so far.
"[We had] little tweaks [between FP1 and FP2], but the car was pretty much the same. There's a particular thing that we left that we're changing to this weekend that we probably need to go back on.
"But it's all relatively close. Otherwise, I think we couldn't do the pace that the other guys did today, but the long-run pace was pretty decent at the end. It just felt as bad as it does normally when it's hot."
Russell stated that he expected FP2 pacesetter Lando Norris and F1 championship leader Max Verstappen to lead the line across the weekend, noting that in Spain and Austria "we were off the pace versus those two drivers, and in the cooler conditions in Silverstone and Montreal, we're ahead of those two."
Mercedes trackside engineering director Andrew Shovlin had noted after FP1 that circuits like the Hungaroring, particularly in warm temperatures, were a key weakness for the team.
He however stated that this was a good opportunity for the team to face up to its challenges and try to put together a longer-term fix.
"We've still got the kind of question mark on performance in rear-limited circuits in hot conditions," Shovlin said. "It's going to be very hot on Sunday. So that's what we're working on. But I wouldn't put us as favourites here.
"It's a good circuit to test that. And when you're trying to focus on one area of performance, if that's rear overheating, the best place to learn and understand your issues is a circuit that exacerbates that problem, even if we'd prefer all of them be like Silverstone. But they're not, and it's a good place for us to work on that problem."
