An F1 pitstop can be completed in around two seconds and is so finely orchestrated that
if even small mistakes are made then catastrophes can ensure.
Like driving off without a wheel attached or even running over a member of your own
crew, which is what unfortunately happened with Kimi Raikkonen’s pitstop in Bahrain.
So what actually happens in those two to three seconds of pit stop pandemonium and how was
is it so easy for mechanic Francesco Cigorini to be accidentally run over?
Let’s start with the setup Formula 1 has the most complex pit stop crew
of any motorsport with so many people servicing one car that you’d need to call 5 taxis
just to get them all home.
Waiting for Kimi as he comes into the pits are:
Three mechanics on each wheel: one carrier to remove the old tyre, another to stick the
new tyre on and a third to loosen and tighten the wheel nut with a pneumatic gun.
One mechanic at either end of the car to operate the jacks and raise the car.
Two mechanics each standing either side of the car to keep it steady while raised.
There are also potentially two mechanics ready to make front wing adjustments.
And there are one or two spotters keeping an eye on pitlane traffic and at least one
mechanic with a fire extinguisher.
Step 1 – Hit the marks The entire crew positions themselves expecting
the car to arrive at an exact position.
If the car overshoot slightly, even by a few centimetres, the crew have to adjust their
position or angles and this costs valuable fractions of a second.
Remember, we’re looking to get everything done in 2 seconds.
If you have to waste half a second adjusting your position, that’s 25% extra time lost.
And don’t forget, the cars are coming in at a not insignificant 80 kmh (or 50 mph).
Often mechanics on the front wheels will wear bright markers on their arms for drivers to
line up their tyres with.
Step 2 – Raise the car Before the car has completely stopped the
mechanics are getting the jacks under the car.
The car sits on the lifting pad right at the base of the jack.
The jacks aren’t allowed to have any powered parts so the mechanics physically lift the
car by levering the jack over its wheels.
While the rear jack is a pretty straightforward device, the front jack is a slightly more
clever swivel-jack design which we’ll get into in a second.
Two mechanics will move in to hold the car steady while its up on its jacks as the tyre
changers aren’t likely to be operating exactly in sync so asymmetric forces will be jostling
the car around at all times.
Step 3 – Loosen the wheel But actually we have to rewind slightly, because
the mechanics on the wheel gun don’t wait for the jack guys to finish before they get
to unscrewing.
The wheels are being loosened even as the car is being raised.
The wheel gun is pneumatic, meaning it’s powered by high pressure air.
It delivers quick and powerful pulses of torque to tightly screw and unscrew the wheel nuts.
I’m going to explain torque in more detail in another video, but whenever you hear people
discuss torque it’s refers to the ‘turning force’ of a motor.
Sometimes that torque is related to turning shafts in an engine, but in this case, obviously
it’s about the turning force on the wheel nut.
Incidentally, the wheel guns torque is about ten times that of a road car engine!
The wheel nut and locking mechanisms are some of the most overly developed parts of the
whole pitstop procedure as the wheel replacement process has to be completed incredibly quickly
but incredibly safely.
Loose wheels are super dangerous due to their weight and instant fines are handed to anyone
who leaves their pitbox with a loose wheel – even if they don’t exit the pit lane.
So how do we screw and unscrew a wheel nut in under 2 seconds and be confident the whole
thing is secure?
Firstly – the wheel nut only has about 3 turns of thread.
That means the spiral screw part is only 3 layers deep so only requires the nut to be
turned three times to be fully screwed in.
Secondly, the wheel nut isn’t separate and loose from the wheel itself.
It can’t pop free of the wheel and roll away.
It’s actually held loosely inside the rim of the wheel itself, which makes things easier
and quicker – though if the wheel nut gets damaged when trying attach it, then it cannot
be replaced and the entire tyre set is ruined.
Thirdly, the axel is nicely tapered meaning the wheel will slip on quickly and easily.
There are also these sprung pins that retract as the wheel is pushed onto the axel and pop
out to lock the wheel in place on the axel, should it come loose.
This is a minimum-level failsafe device as the wheel is so heavy and under so much force
that it can easily wrench itself loose of these pins.
The idea here is that if the loose wheel is noticed quickly enough the car can be stopped
before the wheel escapes.
When removing the wheel, the wheel nut itself holds these pins down, allowing the wheel
to come free.
So, the wheel gun mechanic loosens the wheel nut as the car is being raised.
A second mechanic pulls the old tyre free and a third mechanic slots the new tyre onto
the axel.
The wheel gun mechanic the moves back in to tighten the nut.
Step 4 – Drop the car As soon as all the wheels are physically pushed
on to the axels the jack operators will often start to drop the car.
Both the jacks have quick release handles that the mechanics will pull to drop the lifting
pads.
The pads are sprung and locked in the L position at the start of the stop but instead of going
through the effort of lifting the jack vertical again, the mechanics can simply release the
lifting pad while the jack is lowered.
The front jack is a swivel-jack, which allows the front jack operator to move out of the
car’s way before the jack is completely lowered.
The mechanic can move to the side, with the jack handle swivelling to follow him while
the lifting pad is still under the car.
This means the mechanic can release the jack and pull it out of the way from the side,
saving vital tenths of a second.
Step 5 – Signal the driver to go So now we’re getting to the tricky bit,
and the part of the pitstop that can often be a pain in the Haas.
There used to be someone with a massive lollypop standing in front of the car and if they lifted
the lollypop, the driver knew it was safe to go.
We’ll get onto the pros and cons of that in a second.
Nowadays all the teams use a traffic light system to indicate to the driver when it’s
safe to leave the pitstops.
All drivers do is wait for the green light.
They look at nothing else.
So, what causes the light to go green?
Well, this is a slightly foggy area as every team has its own system but essentially it
works like this (with some variations): The wheel gun mechanics have a button on their
guns that they can hit when they’ve tightened the wheel nut and are free of the car.
The jack operators have buttons on their jacks that they can press when the jacks are lowered
and free of the car.
If all buttons are pressed the light goes green.
Unless – There’s usually a spotter watching the pitlane.
If another car is coming past and releasing the car from the pit box would cause a collision
then the spotter has an override button that keeps or turns the light red.
There may also be a spotter watching the pitstop itself and they too can override the traffic
light if there is a problem like a mechanic in the way, a loose bit of body work, a fire,
etc.
How does it go wrong?
With all these systems in place, you may be wondering how Haas managed to send both its
cars off without tightened wheels in Australia and how Kimi ended up driving off before they’d
even removed one of his tyres.
There’s no definitive answer but most of it falls under the auspices of ‘high pressure
situation’.
It’s likely way too easy for the wheel gun buttons to be pressed, especially if there’s
a problem getting the tyre on and off and they’re faffing around with the equipment.
With twenty-odd people crowded around the car it’s very difficult for spotters to
override the system in time because they can’t actually see everything.
If there’s a problem with the tyre and the car sets off without everything in place,
by the time the mechanics have raised their arms to signal a problem, the car has already
accelerated halfway down the pitlane.
In fact, the raised arms are normally just to make sure the driver gets signalled as
soon as possible.
So what solutions are there?
Lots of ideas a being floated at the moment.
They could bring in minimum pitstop times.
Even raising the minimum to 4 or 5 seconds of stopped time could allow the crew the freedom
to get everything right far more often.
The lead spotter could press a button when the car comes to a halt and the traffic light
simply wouldn’t go green until the minimum time is reached.
They could introduce mandatory pit light signalling systems.
There are lots of ideas available here from a more complicated switch-and-press system
on the wheel guns to having the activator buttons further from the cars so the mechanics
have to literally move away from the car to set off the lights.
Some people have talked about bringing back the lollypop operator.
This could work but it puts a lot of pressure on one person to keep an eye on everything
going on and not accidentally release the driver early.
We’ve seen unsafe releases by lollypop even when the teams had a breezy eight to ten seconds
to wait for refuelling.
They could fall in line with other sports and reduce the number of people working on
the car.
Having one wheel mechanic on each corner of the car would increase pitstop times and allow
that mechanic to be the final word on whether the car is ready to go.
It would also make it easier for spotters to keep an eye on what’s going on.
I don’t think there are any foolproof solutions in such a high pressure situation and the
sport does seem to have a pretty good system considering how few accidents there actually
are.
It’s clear how seriously the FIA take loose wheels and unsafe releases so there is huge
incentive for teams to get it right and not cut corners.
It remains to be seen if any changes will be made but let me know your thoughts in the
comments, particularly if you have any bright ideas!