Valtteri Bottas, Mercedes, Monaco, 2021

Mercedes explain Bottas’ Monaco pit stop failure

2021 Monaco Grand Prix

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Mercedes have explained a slight misalignment between wheel gun and wheel nut caused the machining effect that made it impossible to remove Valtteri Bottas’ wheel.

Bottas’ race ended at under less than half the distance of the Monaco Grand Prix, when a disastrous pit stop saw mechanics unable to remove his car’s front right wheel.

Footage afterwards showed aluminium shearing off the wheel nut, the gun’s force essentially sanding it smooth, rather than connecting to the teeth to loosen the nut.

Chief strategist James Vowles explained “Our nuts are what we call captive, they are maintained within the wheel and the tyre, so as the wheel comes off the nut goes with it.

“This nut has to hold a wheel to the car such it can cope with 5g forces in braking and laterally as well. It’s a huge amount of force going through the axle and the nut and clearly we can never have it coming loose. So, the gun is an incredibly powerful gun, such that you can actually see the mechanics having to restrain themselves holding themselves to the ground otherwise they get rotated with it at the same time.”

He said that the wheel gun’s action, described as ‘hammering,’ required perfect alignment to the nut to work correctly.

“It’s an impact force and what happens is the nut typically loosens in four or five impacts against it, a hammering action.

“What happened is we came on slightly angled, so when the socket was now connected to the nut, it slightly angled relative to it and as a result of that, now instead of distributing the load across all of the nut it was across a small section and that tore the metal clean off and in fact all of the metal was now removed from the nut. As a result of that, the nut was in place and we were unable to remove it.”

The machining on the nut was so severe that Mercedes were unable to remove the wheel in Monaco and were expecting to do so back at their factory.

“Clearly, it’s a circumstance that cost Valtteri dearly and cost the team dearly,” Vowles said. “One that we are going to put steps in place to mitigate.”

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Author information

Hazel Southwell
Hazel is a motorsport and automotive journalist with a particular interest in hybrid systems, electrification, batteries and new fuel technologies....

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49 comments on “Mercedes explain Bottas’ Monaco pit stop failure”

  1. So… not cross-threaded, as had been suggested early on (which seemed implausible given the design of the stub-axle which should make that essentially impossible). Just the wheel gun operator not making proper connection with the nut before the gun started operating.

    Ouch. I guess this is a risk when trying to do a pit stop in 2 seconds, but I’m guessing all of the teams are going to be doing some additional drills on this.

    1. Yes, it sounds like the gun operator pulled the trigger to release the wheel nut a bit too early. Nevertheless, I would have thought Mercedes would have had a backup way of removing the wheel nut, e.g. a wrench, but when you consider that even after the race was over the wheel still hadn’t been removed then obviously there wasn’t any alternative method of removing the wheel nut. When I saw bits of metal flying through the air as the gun operator tried to undo the nut it looked to me as though that was the wrong approach, and that whatever the problem was he was making it worse. Once the nut has lost it’s hexagonal shape then things get really difficult.

      1. The nut isn’t hexagonal, more like castellated with 15 or so slots that the wheel gun socket fits into. There are lots of pictures via google…..

      2. Yes, there’s not much you can do to remove a cylindrical nut.

        On the video you can see the swarf flying out at the first application of the wheel gun, and then the nut with all the splines machined off as the gun is pulled away. At that point, it was pretty much already too late to do anything. Subsequent applications of the gun were just machining the nut ever more perfectly cylindrical, but never had any chance of removing it.

        1. “ViseGrips” … or BFChanneLocks

          1. 2022 Sponsor

          2. Really, really big vise grips :-).

            Or a hacksaw.

    2. Well haven’t you realised the obvious! The wheels were put on before Bottas went to grid incorrectly in the garage, that’s why it wouldn’t come off properly, it was a doomed Pit stop before he was told to box, box.

      1. No. That isn’t it.

    3. I say just get rid of the stupid tire rules. Give each team an allotment per race and let them use them as they see fit. You want 3 hard tires and one soft- go for it! If you win, congrats, if not ,better luck next time. I would have put 3 new tires on and sent Bottas back out.

  2. I am reading that Toto says Valterri stopped slightly off of his marks, and as such the mechanic had to place the gun with an angle….

    1. Yea, the overhead shot shows he is at an angle in the box, (slightly pointing out, and well clear of inner yellow marker line but on the outer yellow.

      1. No, that is not true!
        Look at the footage. There is a line with markings beside the left front wheel. The axel is exactly on the zero mark. So excellent placed by valtteri.
        Toto talks sh#€# again, in regards to valtteri.
        When you listen to the sound you can hear the gun spinning to early.
        Not sure why Toto is sort of blaming valtteri. He did nothing wrong!

        1. Do you want to borrow a pair of glasses? There are four wheels, and if you had bothered looking at the side marks before jumping to conclusions to fit your agenda you will see on one side they would have had to stretch to make the connection, and on the outside the nut would have been presented to them closer than the norm. But you keep making excuses for an F1 driver who can’t parallel park. You do talk some sh#$# at times.

          1. Calm down Ian. Not everyone has an ‘agenda’ – but everyone has opinions, and they are just as valid as yours.
            Bottas was a couple of inches to the right, being a little closer than ideal to the right front wheel gun man.
            Not really a major factor from the driver’s side – this was the wheel gun operator’s issue.

          2. It seems a hit a nerve.
            Bottas was inside the line on the right. He parked perfectly.

    2. @krichelle

      And yet 3 other mechanic’s were able to remove their respective wheel nuts without issue so that really does rule out the slight entry into the pit Box as relevant. Also it’s pretty unrealistic to expect any driver to stop 100% perfectly in the box every single time.

      1. But nevertheless he did so. Exactly on the mark.

  3. I’m amazed that we don’t see that more often. If you watch it closely, about 3 second in (youtube) you can see Bottas comes in really close to the right hand side mechanics, they have to kind of adjust awkwardly. Of course Bottas was very unlucky, but he does kind of misjudge where the centre of his car is, possibly due to the tight Monaco pit lane.

    1. Btw, this is why I’ve often thought having a pit stop for fastest lap just isn’t worth the extra point unless you’re 6th or below. Pit stops can go wrong!

      1. But it depends on the pit crew you have, mercedes proved subpar on this and in particular bottas’. If you go check in the past the amount of time lost by hamilton due to bad pit stops vs bottas there’s no comparison.

  4. Mercedes, what happened?!
    This is not the first time you have problems, at least previously they were less severe…

    Revise these parts already!

  5. I don’t get that wheel guns are not more sofisticated. Why not have rotating self aligning head and gun trigger when correctly in place (triggered by an outer ring pushing against the rim for instance). Is there any restrictions on what they can and can’t do? Is the amount of force too important to have the articulated head?

    Would be interesting to know if different teams have different tools? Or if it’s “just” training that makes RedBull looks so good compared to the rest.

    1. Bending nuts

    2. Yes it is times like this that should make the engineers think along the same lines as you are suggesting. I wonder why they haven’t? After all this is not the first time this has happened. If you knock the corners off a nut with a misaligned spanner there is a spanner available that drives off the flats and the nut can easily be removed. So even if they machined all the corners off the nut the flats shouls stille be there. I am assuming of course that is a standard six sided nut. If it isn’t then maybe they should go back to using one.

      1. Fred Fedurch
        26th May 2021, 21:59

        The nuts are aluminum and have 12 raised splines on them. They get beat up just from normal use, let alone a misaligned “socket”.

        pic links posted on here get held for approval till the end of time, so replace the spaces with “.”

        willthef1journo files wordpress com/2011/04/xpb_425371_1200px.jpg

        formula1 files wordpress com/2014/04/season2014_race4_thursday_4.jpg?w=809

      2. I am assuming of course that is a standard six sided nut. If it isn’t then maybe they should go back to using one.

        I’m sure the leagues of professional mechanical engineers employed by this billion dollar industry will be ready to take your napkin backed advice.

        1. Not to mention that there are generally quite solid reasons to go from a 6-sided nut to a design more like a torx screw – especially with the relatively weak material (aluminium) it makes huge sense to add to contact areas where the gun “pushes” the nuts, given the enormous forces they put through these in very short time spans @skipgamer (well and Patrick), exactly like Fred mentions, these get a lot of abuse during use.

          That nice and six sided nut could easily become a nicely rounded head too given the materials and the forces applied, or see the gun slip on the nut. Especially given a not 100% perfect fit. I would expect the larger contact patches of the nut as is, to offer better potential for actually aligning the nut and the gun in most circumstances without slipping off.

          That how Bottas positioned the car and the mechanic not quite being able to get the angle right worked together in this tight pitlane to get this affect only points to Mercedes possibly wanting to finetune both operations and possibly the detail shape of the nuts.

          I am not sure that having a “self aligning head” would not introduce more uncertainties into the process @jeanrien – it might actually make it harder for the mechanic to precisely target the gun (since they won’t be able to see how the innards are aligned)

    3. F1 in general tries to do thins as simple as possible, in order to eliminate failure points. The type of nuts you mention would surely fail more than the simple ones actually in use.

  6. One thing i don’t fully understand is, the gun is portable right? Would it not just be natural to reposition his arms a little left/right so that the gun connects to the nut properly?

    I guess the time pressure caused the mechanic to force the hammering too early before it aligned. and the slightly off position of the car didn’t help the situation.

  7. JungleMartin
    26th May 2021, 21:27

    This is just a cover story. Hamilton snuck in and fitted that wheel with a nut made of cheese.

  8. Handily, last year Mercedes F1 team appear to have made a video of how it all happens

    Splined nut, internally splined wheel gun socket

  9. I saw a video where it looked like the guy with the new tyre bumped into the guy with the gun just when he put in on the wheel. Could explain it

  10. Yep as expected, the gun wasn’t seated on the nut properly before the mechanic pulled the trigger causing the nut to be damaged to the point of no return.

    Still 100% the mechanic’s fault as 3 other mechanic’s managed to make the slight angle adjustment on their guns before removing them. I’d imagine it’s much easier to twist your body or wrist slightly to align with the wheel nut and unrealistic to expect the driver to be 100% perfectly aligned in the box every single time.

    1. Ambrose Butcher
      27th May 2021, 9:10

      Guys look again the wheel man made an error with the angle or rather height of the gun, yes bumped, yes a fraction off line so what it happens, the guy will be beating himself up and won’t do it again I bet. So it’s all kept as simple as poss to avoid engineering in any more potential issues however when the windy gun isn’t square, and that’s his job, it will form an ellipse, not connect on all splines hence grind them off, PDQ. All the boys have .. almost been there themselves but got away with it, so to finish first first you have to finish. Take care boys.

  11. “Bottas is cursed.”
    -Mercedes explain Bottas’ Monaco pit stop failure.

    1. Bottas is cursed by the team

  12. Incorporating a pin system into the nut, would create a alternative target for torque.

  13. JackFlash67
    27th May 2021, 4:27

    Titanium Alloy wheel nuts

    Light as aluminium. Harder than aluminium. Can be alloyed to be less brittle, thus almost as tough as steel. Still deserves to be properly aligned and engaged before the massive torque hammering of the Wheel Gun sockets… but.. you’d have a much greater margin on RESISTANCE to machining.

    Yes. Ti-Alloys are harder to material procure, more expensive and trickier and manufacture. Ti-Alloys best suited to casting and then NC machining. But I expect the Hi-Tensile Al-alloy versions need NC machining also.

    Pinnacle of Motorsport should be able to handle it.

    1. The main reason for using a material significantly softer than steel is that if it cross-threads, the nut is sacrificed rather than the axle.
      It’s much easier to replace wheel nuts mid-race than stub axles.

  14. So much for hi tec!
    Back to the original 2 winged nut.
    Big hammer to undo & tighten! Simples!
    Stuck nut? Not a problem!
    Don’t force it, use a bigger hammer!

  15. Sergey Martyn
    27th May 2021, 8:08

    A pinnacle of modern technology!

    1. It was sabotage!

  16. Sounds like they’re blaming the mechanic then.
    Win as a team, lose as a team.

  17. “Our nuts are what we call captive,…” Unlike our nuts!!

  18. Unless its left hand thread….
    The initial shower of swarf was thrown clockwise…. So did the wheel man have his gun set wrong…. ?
    Left to Lucy !!! Right to tighty!!

  19. I know everyone is on tenterhooks, so I will report that according to the team’s social media the wheel is now off the car. We can now update Mercedes average pit stop time figure.

  20. Not sure this is convincing. How come misalignment never happened before leading to a result like this? It would make more sense to be a defect on the gun or either having it rotated to the wrong side and therefore destroying the nut. It also could be to start rotating the gun before really connecting to the nut which would be a rookie mistake.

  21. Hi everyone,
    I’m not a F1 fan but love reading comments of anything mechanical. Looking at the gun the forward button is pushed in, the gun actuates all the aluminum is spinning to the right. When the tire man realized it he reversed the gun and quit, good machining job is what I see

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