Mercedes technical director James Allison has explained the cause behind Valtteri Bottas‘ slow pit stop during the 2021 Formula 1 season-opening Bahrain Grand Prix.
The 10.9 second stop took the Finnish driver out of the battle at the front, although he was able to pit again in order to claim an extra point for the fastest lap of the race on top of his third-place finish.
Bottas fell behind Charles Leclerc during the first stint of the race, creating a gap between himself and the front two of Max Verstappen and Lewis Hamilton, but showed excellent pace in his second stint, only for the slow pit stop to scupper his chances of anything better than second.
Addressing the mistake, Allison said Bottas was not at fault and revealed that a misplaced wheel gun was the root cause of the problem.
“When the car came into the pit-stop box, Valtteri came in very neatly, positioned the car neatly and well, which is always a help for the pit crew,” he told Mercedes’ YouTube channel.
“But sadly one of the gun men went onto the wheel, started to disengage the nut, loosened the nut but then started to withdraw the wheel gun just a little bit too soon before the nut had spun off its thread, and because it was still offering some resistance at that point, as he withdrew the wheel gun, the socket on the wheel gun started to disengage from the nut and then started to spin round.
“We call it machining the nut because it starts to chip away at the edges of the nut and destroy the nut, a bit like when you are using a screwdriver and you don’t have it lined up properly, and you start to sort of damage the screwdriver slot.
“So, as he pulled away, the gun machined away at the nut and it didn’t actually come off its mountings.
“He went back in to deal with it but the gun recognises, or is designed to recognise, when it has done a ‘gunning-off’ action and it automatically shuttles the gun so that it is then in ‘doing-up’ mode.
“And so when he went back on to finish the job of taking the wheel nut off, the gun is now in ‘doing-up’ mode and instead of undoing the nut, it is doing it up again and the subsequent sort of follow-on mess of that is what causes something which is normally a beautiful two-second pit stop, causes it to then collapse into something that haemorrhages lap time and seconds in the pit lane.
“But all of it was caused by that initial misplacing of the wheel gun, machining the nut as the wheel gun came off.”