Two Formula 1 teams are scratching their heads as they prepare for the Mexican Grand Prix, following puzzling performance shifts at the US GP in Austin.

Mercedes had shown impressive speed on Friday, but significant crashes for both George Russell and Lewis Hamilton dampened their weekend.

"Lewis apologised, but it wasn't even his fault," said team boss Toto Wolff. "For me, it was 100 percent not his mistake."

Wolff explained that the team's engineers are baffled by how the car was "by far the fastest on Friday," only to suffer a major balance shift and lose pace in the following sessions. He suspects that the new aerodynamic updates are not yet in sync with the car's chassis, causing the inconsistency.

Russell, who crashed, will be forced to use an older floor this weekend due to a lack of spare parts. "The new floor will only be ready for Brazil," Wolff said. "We have the full package for Lewis, but I'm not sure if he'll want to use it again."

It's not just Mercedes dealing with performance questions. Aston Martin also introduced significant updates in Austin, but they failed to provide the expected boost. Team boss Mike Krack said the team needs to review what they brought and assess whether the upgrades will work in Mexico.

"We need to evaluate the changes we made over the weekend and make the right decisions for Mexico," Krack told AS. "But I wouldn't write off the new parts just yet."

Aston Martin had enjoyed multiple podiums with Fernando Alonso earlier in 2023, but progress has slowed since. Krack noted it's critical to understand the developments from 2022 through 2024, especially with the current regulations cycle ending soon. "Sometimes you want to move in one direction, but you have to take a step back first. That's happened to many teams with these ground-effect cars," Krack explained.