The longest pit stop in F1 history: How it all went wrong for Mercedes at Monaco Grand Prix

Valtteri Bottas has returned to the F1 grid this year, and will take his place in Sunday's Monaco Grand Prix. But the track will hold haunting memories for him from 2021.

Bottas was racing at Mercedes at the time, alongside Lewis Hamilton, who was in the midst of a fierce drivers' championship battle with Red Bull's Max Verstappen.

Finnish racer Bottas has only ever secured one podium at Monaco across 11 previous race starts there, but that should have been two podiums and maybe even a Monaco GP victory, if it wasn't for the longest pit stop in F1 history.

Running second in the race at the time, behind Max Verstappen but the leading Mercedes after Hamilton's poor qualifying performance, Bottas came into the pits on lap 30 for what was expected to be a routine pit stop to change his tyres.

What happened next was a disaster for Mercedes and Bottas.

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F1's longest ever pit stop

The problem began when the Mercedes pit crew had to work at a different angle to usual, with Bottas having pulled up just short of the marker when he came into the pits.

This meant that the gun operator for removing the wheel had to put the gun onto the tyre with the handle in an almost horizontal position, rather than the usual 45-60 degree angle.

This unprepared for angle meant that when the pit crew tried to get Bottas' right-front wheel off, the wheel nut cross threaded, and it soon became clear that Bottas was going to have a slow stop.

But more than that, the impact between the gun and the wheel nut led to the metal being machined off, and a big puff of dust could be seen as the front wheel nut locating lugs were torn off.

That's when a frustratingly long pit stop became a retirement for Bottas, with the Finn watching on helplessly.

Former Mercedes motorsport strategy director James Vowles explained at the time: "It's an impact force, and what happens is the nut typically loosens in four or five impacts against it, in a hammering action.

"Now what happened is we came on slightly angled, so when the socket was now connected to the nut, it was slightly angled relative to it and as a result of that now instead of distributing the load across the all of the nut, it was across a small section and that tore the metal clean off."

How long was the longest pit stop in F1 history?

All in all, Bottas' stop at the 2021 Monaco Grand Prix took 43 hours to complete. That's because - with the front wheel nut locating lugs having been torn off - the nut was badly cross-threaded, and Mercedes needed to wait until they got back to their factory in Brackley in order to specially remove the wheel.

That was on the Tuesday, with the race itself having fallen on a Sunday.

That means that for the entire journey back - admittedly not that far in F1 terms - Bottas' W12 had one wheel stuck on it.

The 2021 Mercedes car was a fast machine, but even the team who would go on to secure their eighth consecutive constructors' title later that year could not make up 43 hours-worth of time in a 78-lap race.

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