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Pit Deltas. We all know the term. We kind of have a basic idea of what it means,
but how is it calculated to the point where race strategists can plan around it and construct a
number of race scenarios around it? It’s time for a classic Chain Bear video breakdown.
Let’s start at the beginning. What does ‘Delta’ mean?
Delta is a mathematics term. Basically we wang out the greek alphabet equivalent of ‘D’ – Delta,
seen here in its glorious triangular capital form – when we’re talking about
differences or changes between two things. So if you had two points on a graph,
to compare them and make calculations you might talk about the delta in the x direction and
the delta in the y direction and then you can do things like draw a line and work out the gradient.
Anyway, back to F1. In F1, delta generally
refers to differences between two values. For example, you might hear people talk
about a speed delta, maybe between running with DRS and without. If opening DRS increases your
max speed by 8 kilometres an hour, then you’re talking about an 8 kph speed delta.
It’s all pretty simple really. You might also think about lap
delta or time deltas. This come up a lot under Virtual Safety Car conditions, where cars have
to drive relatively slowly, completing laps at a minimum lap time, measured every mini sector
If, say the Virtual Safety Car minimum allowed lap time is 1 minute 50 seconds and you complete
the lap in 1 minute 51 seconds, then you are ‘delta positive’. Your time is bigger than the
reference time, so the difference between your lap and the reference is a positive number.
If you go too fast, say 1 minute 49 seconds, you are delta negative. The
difference between your time and the reference lap is negative. Your delta is minus one second.
So anyway, on to Pit Deltas themselves. So, when we go to a circuit teams will
work out the difference in lap time between running a normal lap at race speed, and running
a lap in which you have to take a pitstop. The time difference between the normal lap
and the pitstop lap is the Pit Delta. Basically, it tells you how much time
you’re going to lose in taking a pitstop compared to someone who doesn’t pit that lap.
Now it’s worth noting this is different from the ‘total time spent in the pitlane’,
which is often displayed on a graphic during the race. That time just measures the time
span between a car crossing the pit entry line and the pit exit line, seen here on
the Pit Lane Map of the Circuit of the Americas Event Notes map, provided by the Race Director.
So you’ll notice when I did a little graphic of a normal lap, vs a pitstop lap,
I didn’t actually start and complete the lap where the start/finish line actually is. And
that’s because the start/finish line is in the middle of the whole pit stop process
so often part of the pit stopping delta is captured at the end of one lap and part of
it is captured at the beginning of the next lap. So if you want to get a picture of the difference,
it’s best to add up the lap times of both the pit-in and pit-out lap in order to
capture the entire pit delta across both laps Obviously it takes longer to do a pitstop
than it does to not to a pitstop, because not only do you stop, but your speed is massively
restricted through the pitlane compared to cars running at full speed out on track.
There is a speed limit in force between the pit lane start line and pit lane end line.
Each track is different though, with pit lane speed limits that vary, pit lanes of varying
lengths and pit exit and entry paths that deviate from the track in different ways. So the pit lane
delta from track to track can vary massively, with some tracks bearing a huge time penalty from
pitting and others being much more forgiving. So let’s go to the US Grand Prix we just had
and have a look at Verstappen to get a bit of an idea of what a pit delta might be.
The interesting thing about COTA is that the lap time for a pit-in lap is not actually very
different from a normal lap, because the pit entry is shorter than the actual track and the pit lane
start line - where you have to slow for the speed limit - is very close to the start/finish line.
If you compare with with the map for Singapore, you’ll see that there the
speed limit comes into force a lot earlier than the start/finish line so through this
section of the circuit a car out on track will be noticeably quicker than one in the pitlane,
but over at COTA, they will be pretty similar. Anyway, Verstappen then. He pitted on lap 13
so let’s use laps 11 and 12 as our reference for normal racing laps.
Lap 11 was a 1:42.6 and Lap 12 was a 1:43 flat, so added together that’s 205.6 seconds.
He pitted on lap 13, so lap 13 was his inlap and 14 was his outlap. If we add these laps
together they’ll contain the full pitstop within. So that’s 1:42.7 for his inlap and a 2 minute
2.1 for his outlap. Added together that’s 224.8 seconds, so that’s a difference of 19.2 seconds.
That’s just one example though so let’s look at Perez and Hamilton who stopped at similar
sort of times. Perez’s delta around the first stop was about 17.7 seconds and Hamiton’s was
about 20.5 seconds so you’re sort of expecting an 18-20 second time cost for making a pitstop
here. Though it should be noted that Red Bull are generally about a half-second faster at
the actual pitstop part than Mercedes so that’s something you’ll also factor in.
Now, really, the only difference between pitting and not pitting happens between here and here.
The rest of the lap should be pretty similar, disregarding the effect of a new set of tyres.
But when pitting there are, I guess, four phases that are different from taking a normal lap
There’s the stop itself, where the car is stationary for 2-4 seconds in its box.
There’s the travelling through the official pit lane bit in the
section that’s actually speed limited. And then there’s the entry and exit to
the pit lane, which isn’t speed limited but will require you to decelerate from
racing speed on entry and accelerate back up to racing speed on exit, so we’re really
talking from the pit entry road right up to the first corner you encounter back on track.
Also the pit entry and exit lanes may deviate wildly from the actual circuit. While COTA and
Singapore follow the track pretty closely, Silverstone takes a massive shortcut on
entry. So much so that the speed limit is slow and it starts very early to stop the
pit lane actually being a shortcut in itself. Sao Paulo’s pit exit is very long and winds
past the exit of turn 3 before emerging down the back straight. All of these effect the overall
pit delta and must be factored into strategy. But the reason I stress that only this part
is important for pit stop time loss is what happens when there’s a safety car.
Teams will often try and stretch a stint out if there’s risk of a safety car or virtual safety car
because pitting under a safety car costs so much less time that it does under normal conditions.
This is what they call a ‘cheap pit stop’. And why is it so cheap?
Well, the time spent in the actual speed limited part of the pitlane is identical,
whether there’s a safety car or not. You’ll still be going the same speed,
regardless. And the time spend in the pit entry and exit lanes will be virtually identical too.
However, out on track, everyone is limited by the pace dictated by the Safety Car or Virtual
Safety Car. But to reiterate, the absolute time of taking a pitstop (basically that ‘time spent
in the pitlane’ graphic) remains almost identical. So let’s look at this using some real data again.
There was a Safety Car in the US Grand Prix. Let’s look at it on the actual F1 Timing App (which is
well worth a sub if you like following live data) So this is lap 14. It might be hard to see but
there is a little mark on the circuit here before turn 20 so we’ll time the cars going
from here to the apex of turn 1. The pitlane is here, by the way.
So let’s look at a normal racing lap. I’ll speed it up, i’m not a monster… and
we see that it takes Verstappen 16.22 seconds to complete just racing the track normally.
If we look at the end of lap 13, when he took a pitstop we can see he disappears while in
the pits but pops out again at the other end and ultimately takes 36.3 seconds to complete
the same distance. And we agree this time is baaaasically the same time no matter what because
it’s not limited by the safety car speed. Now the Safety Car was called on lap 18 but
didn’t pick up the pack til turn one of lap 19 so the cars were running to a reduced lap
delta til they caught it up. So in this period, Verstappen took 20.26 seconds to
travel this distance. A little longer. And under full Safety Car conditions,
with the Aston Martin leading the train of cars, obviously it took longer still with Verstappen
taking 24.5 seconds to travel the same distance. So bearing in mind that the time it takes to
travel between here and here while taking a pitstop (about 36 seconds)
will remain the same whether it’s green flag running or under some kind of safety car,
we can see that a normal delta is about 20 seconds The delta while the safety car had been called,
but the cars weren’t yet in the train was about 16 seconds (so a pitstop here would
have been about 4 seconds faster than normal) And while the cars were behind the safety car,
the pit delta was only about 12 seconds, a saving of about 8 seconds over a normal pitstop.
Now, the teams will be able to simulate all of this before they even turn up at
the track. They’ll have a decent idea of the pace of the cars, the pace of the
safety car, and the time through the pitlane, including accelerating out back to track speed
so they’ll arrive with all those numbers in hand. But practice, including when the safety car does
practice runs will help make those numbers more concrete so strategies can be put in place for
the Sunday race. If rain falls, that makes things extra tricky because there’s no definitive ‘wet
lap time’ as this varies massively depending on conditions so a lot of these calculations are
crunched on the fly as the track evolves and the chances of safety car come in and out of favour.
So that’s the Pit Delta and how it can change from circuit to circuit and be
massively shortened by a Safety Car. Probably something you instinctively
knew but now you have the visuals to help understand it completely.
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