How the pursuit of marginal F1 gains caused Sauber's pitstop stumbles

One crumb of comfort Valtteri Bottas can identify as he contemplates an early season blighted by pitstop issues – none of them will be as bad as his worst stop ever, which remains a record in Formula 1. At the 2021 Monaco Grand Prix, when Bottas was driving for Mercedes, the pit crew was unable to remove his right-front wheel… so it remained in place for another 43 hours, finally parted from the chassis in a surgical procedure back at the factory.

To consistently achieve fast stops, where the car is stationary for around two seconds, teams not only practice the procedure itself regularly, they develop bespoke technologies to expedite the process. While ultra-fast stops are desirable – and rewarded with a nice-to-have but somewhat pointless award sponsored by DHL – most team managers will tell you they prefer to target a consistently quick average rather than chasing peaks, which is when mistakes can creep in.

That’s what happened to Bottas in Monaco: he fractionally overshot his marks, forcing the crew to shuffle up, so the wheelgun operator came in at an angle and the gun sheared off the nut’s engagement lugs. The issue that has beset Sauber during the opening races of this season comes from a different place, and is understood to be a design and metallurgical issue with the wheelnuts themselves rather than a series of operational blunders or equipment malfunctions.

At the time of writing, ahead of the Japanese GP, Sauber had suffered cross-threaded nuts at all three opening rounds, each afflicting the front-left corner of the car. It has adjusted procedures to compensate but this is a sticking-plaster since a proper solution requires design changes and new components.

 In Bahrain, the team achieved reasonably quick stops for Zhou Guanyu (3.03s and 2.77s, compared with a fastest of 2.23s at Charles Leclerc’s first stop). But for Bottas’s first visit his car was stationary for a somewhat tardy 4.30s – then a disastrous 52.44s at the second. In the one-stop Saudi Arabian Grand Prix, Bottas was held for 3.62s while Zhou had a cross-threaded front-left that left him stationary for 28.71s.

These were embarrassing if not, in the final analysis, damaging in terms of points. Then
came Australia, where a 31.18s stop for Bottas – this after the team had introduced countermeasures for the problem – cost a potential top-10 finish. Given the speed and reliability of the top five teams, opportunities for the other half of the grid to score points
are likely to be rare and highly prized.

A painfully slow pitstop in Australia cost Bottas a good shot at points

Photo by: Zak Mauger / Motorsport Images

“There has been progress,” says Bottas. “There have been modifications to the procedure and some of the materials we could use. Some of the measures have been taken, it’s not still 100% fixed unfortunately, but, again, the chance of having an issue should be lower. Basically, we didn’t know before the season that it would be an issue and it’s not a quick fix. There’s a 100% fix planned for China.”

Custom made

Every team has its own pitstop procedures, though the number of personnel required is usually similar – around 20. While the wheelguns themselves are sourced from an Italian company, Paoli, there’s a high degree of customisation: external surfaces are ergonomically sculpted to accommodate individual hand positions, plus each team has its own system of enabling mechanics to signal that they’ve completed the wheel change. Only when all four corners have given the all-clear will the gantry light system release the driver.

The sockets at the end of the guns are also bespoke, since the wheelnut design is unique
to each team – as is the threading that governs how many rotations are needed before the nut meets the face of the wheel, where it’s tightened to around 4000Nm.

Since the Sauber C44 has no carry-over suspension elements from last year’s car, reverting to the 2023 wheelnut design wasn’t possible. Instead the team has had to redesign both the wheelnuts and the front hub carriers

As with any other element of an F1 car, there are trade-offs to be made in the name of performance and teams have invested heavily in finding marginal gains – such as the ‘sweet spot’ in thread design, which blends retention strength with as few rotations as possible to full tightness (even at the wheelguns’ 14,000rpm, an unnecessary extra spin is time wasted). It’s understood Sauber has pursued an aggressive lightweighting strategy for the wheelnuts on the 2024 car, and the cross-threading problem has been caused by heat build-up in race conditions – potentially exacerbated by the first three races being held in relatively warm environments. All these factors are difficult to simulate pre-season.

“From the first race, we found some issues with the pitstops, with cross-threads,” says head of trackside engineering Xevi Pujolar. “When we do free practice, or even during the winter, we didn’t have a problem but then every time we go into a race situation, it becomes more critical.”

“Even in the [Bahrain pre-season] test, it wasn’t a big concern,” says Bottas. “But then
we started to see some issues. I was disappointed, but the whole team was disappointed because these things shouldn’t happen. So we’re definitely taking it seriously and it’s been a priority to get it sorted. I think it will also be important for the pit crew to have clean stops, for the confidence.”

Bottas still holds the unwanted record for longest F1 pitstop

Photo by: Steve Etherington / Motorsport Images

Since the Sauber C44 has no carry-over suspension elements from last year’s car, reverting to the 2023 wheelnut design wasn’t possible. Instead the team has had to redesign both the wheelnuts and the front hub carriers, hence the delay while these are manufactured.

Minimal testing is now baked into Formula 1’s cost-controlled financial ecosystem. And while many engineers and pundits enthuse about the increased fidelity of simulations, this has been a salutary reminder to the entire grid that the only way to prove a design definitively is in the heat of competition.

Sauber aims to have a permanent pitstop problem fix by the Imola F1 round

Photo by: Andrew Ferraro / Motorsport Images