Plank worn out. After every race, the car inspection takes place wherein various parameters-- weight, dimensions, thickness, front floor deflection test and more -- are carried out. At the US GP, things turned a little sour for Lewis and Charles as both racers were disqualified for excessive plank wear out. Lewis had a clever P2 finish in the race, whereas Charles finished P6. However, due to the Technical Delegate's report, the wear out of the skid plate was outside of the thresholds outlined in Article 3.5.9 e) of the FIA Formula One Technical Regulations, which also includes a tolerance for wear. According to the Article 3.5.9 of F1's 2023 Technical Regulations- "The thickness of the plank assembly measured normal to the lower surface must be 10mm [plus or minus] 0.2mm and must be uniform when new. A minimum thickness of 9mm will be accepted due to wear, and conformity to this provision will be checked at the peripheries of the designated holes." And in both these driver's car cases, the thickness of the plank was below the limit of 9mm, thus the disqualification.
There are several varied factors that have led to such excessive plank wear. Well, teams don't run the cars with heavy fuel in the practice session; hence, uncovering the perfect setting for the car up for the race becomes tough. The track was tricky, and drivers did face a bumpy ride. On top of that, Mercedes had brought in the new floorboard for the US GP. In contrast, Ferrari didn’t bring any upgrades to the floor, it seems to be an external reason behind the failure of the plank test.
Both the teams seemed a bit disappointed after the disqualification result, so they sent their representative to speak to the Stewards about the judgement. They said, "the high wear on the skid pads was probably a result of the unique combination of the bumpy track and the Sprint race schedule that minimized the time to set up and check the car before the race." In response, Stewards stated, "the onus is on the competitor to ensure that the car is in compliance with the regulations at all times during an event. In this particular case, the rear skid in the area defined in the Technical Delegate’s report was outside of the thresholds outlined in Article 3.5.9 e) of the FIA Formula One Technical Regulations".