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Formula 1 United States GP

How did Mercedes and Ferrari fall foul of F1’s plank rules?

Lewis Hamilton and Charles Leclerc’s post-race disqualification at the United States Grand Prix was the first time in years that cars had fallen foul of Formula 1’s plank rules.

Mercedes W14 plank detail

In fact, there have been remarkably few times in F1’s history that planks have been found to have worn down too much – with the most famous still being Michael Schumacher’s disqualification from the 1994 Belgian Grand Prix. 

This makes it even more intriguing that, in an area of the car that teams are very mindful of there being no room for error, two of the top squads tripped up on the same race weekend. 

The explanations as to how the rule breaches happened seem to be clear, which is why both teams had to simply accept their fate with the stewards once the planks were found to be worn away too much. 

As Mercedes boss Toto Wolff said: “There's no wiggle room in the rules. We need to take it on the chin, do the learning, and come back stronger.” 

What the plank rules say 

The tolerance between success and failure over plank legality is tiny, given there can be no more than 1mm of wear between a freshly fitted plank and one that’s gone through all the rigours of a race. 

To check compliance with the rules, the FIA is able to measure wear on the plank at four 50mm diameter holes drilled into the surface at specific locations designated within the technical regulations.  

In the instance of Leclerc and Hamilton, it was the rearmost hole that failed the test. This hole must be positioned on the car’s centreline between 825mm and 1025mm ahead of the rear axle line.  

As can be seen from the main image, this in itself offers some variability as to how wear can occur on different cars, given that there is not a specific point for the drill hole, unlike the three holes at the front of the plank. 

The drill holes made in the plank (which is no longer made of wood, rather it is a composite material) are surrounded by flush mounted titanium skids.  

These offer further protection from wear and are also tightly regulated in their design. This is an area that the FIA has been closely monitoring with this new generation of cars, and it has served several technical directives as a response to inconsistencies in their design already. 

Lewis Hamilton, Mercedes F1 W14, Charles Leclerc, Ferrari SF-23, Max Verstappen, Red Bull Racing RB19, Carlos Sainz, Ferrari SF-23

Photo by: Steve Etherington / Motorsport Images

Lewis Hamilton, Mercedes F1 W14, Charles Leclerc, Ferrari SF-23, Max Verstappen, Red Bull Racing RB19, Carlos Sainz, Ferrari SF-23

One interesting discussion point after the disqualifications was that the FIA did not check the planks on all the cars. 

This is standard procedure as it would be impossible for the governing body to check compliance on every aspect of every car after every qualifying and race. It is why it selects random elements each time from random cars in a bid to check compliance. 

On this occasion, Max Verstappen’s RB19, Leclerc’s SF-23, Hamilton’s W14 and Lando Norris’ MCL60 were all chosen to have their planks checked. 

The Red Bull and McLaren were given the all-clear, whereas the Ferrari and Mercedes were not. 

The trigger points 

The technical reason for why the planks were worn too much is simple to explain. The cars were running too low to the ground, and this scuffed them away over the Austin weekend.

The cause of this revolves around the choice of rear ride height, something that teams play around with each weekend. But it can also be influenced by fuel loads and even DRS use – as the aero load comes on and off the car.

Teams normally have plenty of time on a grand prix weekend to get their ride height into a sweet spot where the plank is not at danger of being worn away – but the car is low enough to deliver maximum performance.

However, this balance has proved harder to manage at sprint races with teams having just one practice session – rather than the three of a normal F1 weekend – to lock settings in before qualifying. 

As a consequence of the more condensed timetable, there is an inability to cover the qualifying and long run programmes that are regularly done. 

Any ride height calculations being made during this FP1 session must account for the additional competitive running that is added into the weekend’s schedule, as there are extra competitive sessions taking place once car settings are locked in.

McLaren MCL36 plank

Photo by: Giorgio Piola

McLaren MCL36 plank

Furthermore, teams are not able to check the plank wear as freely as they normally are once the cars are in parc ferme, so there is a certain element of guesswork going on. 

We have already seen times this year, like with Alpine in Baku, where teams have realised after the sprint that the ride heights were too low and there was a risk of the plank being worn too much in the main race. Cars have been pulled out of parc ferme to make ride height changes, and started from the pitlane. 

Ferrari revealed after the race that it had spent time during FP1 raising the ride height of its cars in order to find an optimum range for the race weekend once it became clear how the bumps were impacting things. 

But it clearly did not raise the car enough though. Intriguingly, it also suggested that the weather may have played a factor in how things played out. A stronger wind intensity than was originally forecast, along with a change in direction, perhaps meant the car was being forced down further in areas of the track than it had in practice – pushing the plank on to the ground. 

The situation at Austin was also made more complicated by the bumpy nature of the circuit, which was described by Verstappen as not being up to F1 standard. 

Another potential factor would also be related to tyres, as it may not be a coincidence that the two cars that fell foul of the plank issues were those that ran extended opening stints.  

We know that, as the tyres wear, there’s less tread left, which not only reduces grip but means more temperature is able to escape. This can result in lower pressures as tyres get towards the end of their life, and that has the consequence of a lower ride height.  

In both Hamilton and Leclerc’s case they ran longer first stints on the medium tyre in order to create a strategic offset to Verstappen and Norris - with Leclerc opting to make a one-stop strategy work against his rivals on two-stoppers.  

This could have opened the door for extra plank wear in this period of the race, when the car still quite heavy with fuel. 

George Russell, Mercedes-AMG, in Parc Ferme

Photo by: Zak Mauger / Motorsport Images

George Russell, Mercedes-AMG, in Parc Ferme

Lessons learned 

All these above elements came together to push the Mercedes and Ferrari outside of the tolerated window. 

As Mercedes trackside engineering director Andrew Shovlin explained: “Unfortunately, it is one of the pitfalls of the sprint format where we have a solitary hour of running before parc ferme.  

“Without running at a race fuel load in FP1, combined with a circuit as bumpy as this and the parts of the track where the drivers have to put the car during the grand prix, have contributed to the higher than expected wear levels. We will go away and learn from this.” 

It will be interesting to see if at bumpy sprint venues – with Interlagos coming up – teams now change their programmes in FP1 to ensure that they get at least one run on heavy fuel to better understand ride height implications. 

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Furthermore, the disqualifications of Hamilton and Leclerc will likely prompt some fresh debate about whether or not the parc ferme rules are a good fit for the sprint weekends in terms of locking teams into set-ups so early. 

Amid talk of a sprint race format rejig, the parc ferme rules could well be changed to help avoid a repeat of what happened at Austin.

While Ferrari and Mercedes may feel slightly hard done by, they will perhaps be slightly relieved that their other drivers didn’t suffer the same fate, seeing as post-race checks were not performed on every car.

The question everyone is asking now is just how many other cars would have failed the plank checks if the FIA had looked at all competitors?

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