Why McLaren was the surprise casualty of plank wear bust in Las Vegas

There is a venerable Tommy Cooper joke which goes something like this: "I went to the doctor the other day and I said, 'It hurts when I do this' [raises arm to shoulder level]. He said, 'Well don't do it, then…'"

Exclusions for plank wear – and related matters – have grown increasingly common in the ground-effect era, given the importance of ride height to generating and maintaining negative pressure under the cars. Lewis Hamilton has been struck out twice (in the 2023 US GP and China this year), Charles Leclerc once, all of which cost their teams points, while Nico Hulkenberg's disqualification from 13th in Bahrain this year at least didn't affect Sauber's constructors' championship position.

Perhaps most costly of all was George Russell's victory in Belgium last year being struck off. While that was for the car being underweight, Mercedes cited plank wear as a contributory factor.

The obvious solution might appear to lie in following the spirit of the Cooper quip and simply running the cars higher to avoid wearing the planks in the first place. But to suggest this would be to misunderstand how ground-effect aero works: the suction effect under the car naturally draws in air from the sides as well as painting the car to the track.

Without an effective seal at the sides, all that hard-won downforce bleeds away as the incoming air reduces the amount of negative pressure. As the cliché goes, nature abhors a vacuum.

In F1's previous ground-effect era in the late 1970s and early 1980s, teams achieved this by fitting skirts which physically sealed the floor edges – in theory. In practice, these either wore away or, when teams shifted to retractable sliding skirts, jammed in position as the chassis flexed. One of the reasons for the Williams FW07 blowing rivals away was that the team was careful to design a rigid enclosure for the skirts within the sidepods.

McLaren's double DNF in Las Vegas has blown the title race open

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Under the current ruleset, teams sculpt flow conditioners into the floor edges to set up vortices which redirect air that would otherwise be drawn into the underfloor. But these become less effective at higher ride heights.

The upshot is that competitors still have to run the floors as low as possible to maximise downforce, and live with the risk of wearing the plank. Thus many of them have devised means of exploiting the rules governing the metal skid plates which are incorporated into the planks in various places. 

Each plank has four holes which are used to measure wear during scrutineering via a depth gauge inserted into them. Teams are permitted to fit titanium skid blocks around these holes, and used to be able to incorporate so-called "satellite skids" further away, but this latter practice was outlawed in a technical directive issued ahead of last year's Las Vegas GP.

The Las Vegas disqualification indicates the difficult compromises inherent in the current ground-effect era

After the Brazilian GP this season there was intrigue over whether some teams were heating their skid blocks before track sessions to provide additional protection for their planks, since metal expands when heated. Titanium has a lower coefficient of expansion than steel, so the effect would be quite marginal, but in this environment every millimetre can be worth tenths of a second. It is also less thermally conductive than the likes of steel and aluminium, so it tends to retain heat.

It's claimed that a technical directive specifically outlawing this practice was circulated to the teams. But the rumour, while interesting, fails to account for the fact that it is the skid plates themselves rather than the plank which is measured, rendering such metallurgical mallarkey futile.

The reason for both McLarens being excluded from Las Vegas was more prosaic: the team simply misjudged the delicate set-up balances required to achieve a minimal ride height while protecting the plank. Both cars were over the limit at the front and rear.

McLaren's success in running its car low without wearing the plank has been key to its success

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McLaren's pace advantage throughout this year is widely believed to stem from it finding a way to run its car so the rear of the plank is less marginal. This is the code Red Bull finally cracked with its most recent updates, having expended much energy under its previous leadership circulating absurd conspiracy theories about illegal tyre cooling.  

But the Las Vegas disqualification indicates the difficult compromises inherent in the current ground-effect era. Track conditions changed throughout the weekend: it was colder and windier than expected on the first day of running, and FP2 was disrupted by red flags; then it was wet on qualifying day, while race day was much less cold than before. All of that would have contributed to entering the race with a sub-optimal set-up.

Oscar Piastri had laboured throughout the weekend and his race pace is difficult to judge because he was biffed by Liam Lawson at Turn 1, incurring damage. Lando Norris had enough pace to see off Russell for second place, especially when he was running in clear air – until he had to fuel save in the final laps, of course – but he clearly had no chance of catching Max Verstappen.

No sooner had the instruction come from the pitwall to "Go after Max" than Verstappen simply dipped into his reserves and went faster still – to the extent that Red Bull driver advisor Helmut Marko was still chuckling about it after the race.

"It was an unbelievable Max Verstappen show," he said. "He forced Lando into a mistake in the first corner. And then he was controlling the race more or less. We stayed out longer than Mercedes and McLaren. And the most exciting thing was when McLaren told Lando ‘now you have to attack and overtake him'. And then – poof, poof, poof, one fastest lap after the other was coming."

McLaren team principal Andrea Stella's statement issued in the wake of the qualification supports the theory that the set-up went awry.

Regardless of the disqualification, McLaren had no answer to Verstappen's pace in the Red Bull

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"During the race, both cars experienced unexpected, high levels of porpoising not seen in the practice sessions, which led to excessive contact with the ground," he said. "We are investigating the reasons for this behaviour of the car, including the effect of accidental damage sustained by both cars, which we found after the race, and that led to an increase of movement of the floor. As the FIA noted, the breach was unintentional, there was no deliberate attempt to circumvent the regulations, and mitigating circumstances also existed."

If you were wondering why it took the best part of two hours between the cars being cloistered in the garage behind closed doors and a verdict emerging, it's understood that Stella, along McLaren technical director Neil Houldey and racing director Randeep Singh, diligently argued every detail with the FIA's Nikolas Tombazis and Jo Bauer.

Ultimately, the unexpected porpoising, changeable weather and truncated practice sessions were deemed insufficient mitigation, as was the team's contention that the extent of the breaches were less than those which caused Hamilton and Hulkenberg to be disqualified earlier this season. So too was the argument of accidental damage.

McLaren will be thanking its lucky stars that it is heading to smoother tracks in warmer climes

As the stewards finding pointed out, "There was no provision in the regulations or in precedent for any penalty other than the usual penalty (i.e. disqualification)...The Stewards also note the various decisions of the FIA International Court of Appeal which limit the ability to avoid disqualification for technical breaches."

There was no way to wriggle out of it because there was no wriggle room in the rules.

So, Verstappen's points total now equals Piastri's, and he lies just 24 behind Norris with 58 possible to score in the remaining rounds. McLaren will be thanking its lucky stars that it is heading to smoother tracks in warmer climes.

Can McLaren fend off Red Bull for the drivers' title?

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