Enforced Two Stop Strategies
There was a bit of talk in the last month about creating a rule to force drivers to
take a minimum of two pits stops per race to improve a race’s overall interestingness.
I thought it’d be interesting to have a look at how that might work and why some people
think that’s a good idea.
First, let’s create a very simple model of how tyre strategies work.
And I mean super simple.
I want to strip away all the equations and multi-variable modelling that goes into planning
a race and just think about the basics of constructing your strategy.
So let’s just assume a 30 lap race for this model.
And we can use little blocks to represent units of time.
It doesn’t really matter how much time each block represents as you’ll soon see this
model sort of lives in its own world.
Let’s say a Soft tyre gives lap times of 7 units for the first 6 laps of its life.
Then the laptimes get longer and longer as the tyre dies off.
The Medium Tyre is slightly slower but lasts longers before it drops off and the lap times
increase.
The Hard tyres again are a bit slower but last even longer than the Mediums.
OK, so let’s say a pit stop in this model costs you ten units of time so now we can
have a quick look at a two stop strategy vs a one stop strategy in this model.
On our one stop strategy we do nine laps on the medium tyre, before it drops off, then
we’ll do the rest of the race - 21 laps - on the hard tyre.
The end of our hard stint has this drop off start to kick in but
a) we did save an entire pit stop and b) maybe we can manage that wear by backing
off in general throughout the stint to extend its life a little bit.
We have that option.
Our two stop strategy might be that same nine lap stint on the mediums, then another nine
lap stint on the mediums, then just 12 laps on the hard tyre.
So here we had to do take two pitstops but a) we’re running on the faster tyre for
longer and b) we never hit the drop off on the hard tyres
so can push for pretty much all of our hard stint without worry.
And, if we add up the total times of these two strategies we can see the two-stopper
is a bit faster than the one-stopper, here.
So a two-stop is a no brainer, right?
Well, not quite.
See, while - yes - overall, the total times suggest the two stop being the fastest, we’re
not taking into account how things play out on track.
Let’s have a look at how this would look on a lap chart.
So this line chart just shows the total time taken over the course of the race.
This pink line represents our two stop and the blue dotted line represents our one stop.
Obviously for the first 9 laps they are on the same tyre so race identically.
They pit together, here.
But now, for the next nine laps, Pink is on a faster tyre so is accelerating away from
Blue on the hard.
On this chart, Pink is lower than Blue as they’re taking less time to complete each
lap.
However on lap 18, Pink has to pit again and now falls behind Blue.
Pink can’t make any headway on Blue, really, until the older sage of Blue’s tyres start
to kick in around lap 26 This idealised lap chart shows that Pink overtakes
around lap 28, just a couple of laps from the end.
But, we’re forgetting - overtaking isn’t easy.
We know this very well.
Pink could easily get stuck behind Blue in the last couple of laps and not be able to
overtake.
This is particularly true if Blue takes it a bit easier through their stint to extend
the life of the Hard tyre.
Pink will catch them earlier but Blue will have more life left to fight with.
And when Pink is stuck behind Blue, that takes extra life out of Pink’s tyres as they start
sliding around and overheating in Blue’s dirty air.
Plus, this race isn’t just about Pink and Blue.
Pink doing an extra stop puts Pink at risk of not only extra traffic but also having
to overtake more front-running one stoppers than just Blue.
Two-stopping may be faster in a vacuum, but it’s a lot riskers and if the time difference
is marginal, it’s often just not worth it.
That’s why we see a lot of races lately where most cars go for a one-stop strategy
and then spend most of the race conserving their tyres for the long haul.
There’s less racing and a lot more tyre management.
Kind of the opposite of what fans want, but it’s the only sensible approach to the race.
You can’t really blame them for going this way.
So, what if we force teams to two-stop, then?
We can do this in two ways.
One is the way Pirelli tried and arguably failed to do this year which is by constructing
the tyres such that the life of the rubber makes it more sensible to do two stops.
There’s a couple of methods to pulling this off: one is to build a ‘cliff’ into the
tyre performance.
This means that after a certain point the tyre just dramatically gives up and your lap
times just whoompf!
This essentially creates a hard limit on tyre life - 7 laps for softs, 12 for mediums, etc.
Alternatively, you could design tyres such that the speed at which they lose performance
creates natural crossover points so that after a certain number of laps the harder compounds
of tyres become faster.
There’s no dramatic cliff but a wider amount of time in which you could think ‘OK, it’s
probably worth getting off these tyres now; I’m losing too much time’.
Pirelli used to go for the ‘tyre cliff’ option, which did actually generate plenty
of exciting races with mixed strategies and overtaking.
But they steered away from this philosophy as some people complained the tyres were too
much the focus of a race and there were some risk issues around tyre blowouts, highlighted
particularly at Silverstone in 2013 when it was like a rubber fireworks night out there.
What’s being suggested now, though, is instead of trying to force the teams into two stop
strategies by reducing the tyre life, why don’t we just say ‘you have to do at least
two pits stops’?
Right now we have a mandatory single pitstop by virtue of the two-compound rule, so why
not just tell them to do two pit stops instead?
This means one-stop strategies go out of the window.
So now we can think about how two-stop strategies might work against each other.
We could stick with the Medium-Medium-Hard strategy that worked so well before or we
might want to go with the slightly faster Soft-Medium-Hard strategy (which I’ll colour
in Green).
Even though it does bring you out behind Pink every time you stop, Pink then pits before
you close up and need to overtake them so that could be good if you’re not held back
by a sneaky wingman extending their stint.
Choosing which strategy you go on will depend on what’s going on around you.
You might change your Medium-Medium-Hard to a Medium-Soft-Hard strategy if you think you
can use this fast middle stint to pull off some undercuts.
It’ll only work if you don’t spend these 7 laps stuck behind anyone at any point, though.
We could even try for a three stopper.
Soft-Soft-Soft-Medium is by far the fastest ideal strategy on paper but in the reality
if would struggle against a one stop because you’d have to keep re-overtaking lots and
lots of cars every time you pitted which would kill your momentum and probably your tyres.
Against two stoppers, though - you might just take the risk if you were feeling racey and
traffic was good.
Basically, enforcing two pit stops could move strategies back to the kind we had during
the refueling days where the advantage for stopping more times but keeping the car light
would far more often outweigh stopping fewer times with a heavy car.
Again, this is a just a simple model to explain the thinking behind the idea.
It gets a lot more complicated in practice and requires the tyres to be made such that
their degradation compliments this kind of strategy.
The downside here is that more pit stops and mixed strategies could lead to a lot of the
position changes happening through the pits and not on track.
But then again, we’re not seeing much on track action at the moment so maybe this is
a good way to inject some excitement into the race.
Maybe two-stops will give a car on faster tyres the ability to overtake their harder-tyred
rival.
It’s not a fair fight, necessarily, but then the leading car need to get fiercely
defensive to force their own strategy to succeed, and that’s often a lot of fun.
There’s certainly a lot to think about.
Obviously the best solution is to find a way to get the cars able to fight each other on
track.
That way, a slower one-stop strategy cannot rely on those faster two-stoppers unable to
overtake.
Either way, it would be nice to see the end of one-stop, conserve-and-block strategies.