Max Verstappen fears Red Bull's long run pace is "nowhere" and gives him little chance of winning Formula 1's Mexican Grand Prix, despite topping the opening day of practice.
The Red Bull driver looked comfortable on the short runs in FP2 on Friday as he edged out Charles Leclerc's Ferrari by 0.153 seconds.
But the contrast between that promise and struggles he felt on a medium long run could not have been greater.
"On the soft we managed to do a good lap," he said afterwards. "The rest: everything else was pretty bad.
"On the medium, the short run was not great. And the big problem is the long runs, where we seem to struggle a lot. So that is, of course, a big concern for the race."
Asked what he felt had caused the problems, he said: "I don't know yet. The balance wasn't even off. It was just no grip, and that is the bigger, bigger concern.
"So as soon as you go on a sustainable run, the tyres are going hot. We were nowhere. So that is a tough one, I think, to sort out as well, but we'll see."
While track position is so important this year, so the single lap pace should give some encouragement for qualifying, Verstappen is clear that Red Bull needs to find improvements overnight for the long runs if it is going to be able to capitalise on Sunday.
"You're not going to win the race like that," he said about the long run deficit. "You can be fast over one lap, but if you have absolutely zero pace in the race, then it's going to be very tough. So I prefer to be fast in the race and not so fast over one lap."
Red Bull head of racing Gianpiero Lambiase believed the contrast between the strong single lap pace and the long run struggles was most likely tyre temperature related.
More specifically, it is how the Red Bull manages both the core and surface temperatures to fire up the tyres perfectly for one lap but then not overheat for race runs.
"The challenge we are working on at the moment is really trying to find that combination of tyre inner and surface temperature," he said.
"Certainly in FP2 we saw that the long runs are becoming more and more of a focus for us.
"I think over one lap both cars are able to put in quite a competitive lap time, as you saw in FP2, particularly with Max. So, it's the high fuel run pace where we are really having to focus all of our attention this evening.
"We feel we are not really in a happy place with our tyre degradation and thermal control of the tyre. We need to work to get that where we need and want it to be."
Piastri in less trouble than he looks?
Verstappen's victory in the United States Grand Prix last weekend put him firmly in title contention, but with a 40-point deficit remaining to championship leader Oscar Piastri, he cannot afford to lose any ground.
Piastri himself had a scrappy low fuel run in practice, ending up 12th overall, but was not too despondent about his prospects.
"The lap on softs at low fuel was pretty average, so I'm not surprised with the lap time," the McLaren driver said.
"We tried a lot of things, we'll go through and have a look at what worked, what didn't, but overall I felt reasonable.
"We will see what we can tune up for tomorrow to try and make things just a bit more consistent. I think that is the biggest thing."
