The Mexico race is an outlier on the Formula One calendar due to its altitude.
The effects from being so high above sea level saw a slight shifting of the power structure
in F1 with Red Bull and Renault in particular able to show particularly strength.
So what effects come out of racing at high altitudes?
Well, as someone on a mountain once said: “Let’s start at the very beginning.
It’s a very good place to start.”
OK - so the thick and thin of the matter is that all of the curiosities of racing at higher
altitudes come from the change in air density.
You can think about all of the air around the world as a giant sea of air molecules
to some extent.
But, unlike liquid, air is very compressible - if you squish it up, all the molecules will
move closer together.
So you can see, the air right at the bottom of the atmosphere - the air right down at
sea level - has all of the mass of the air above pushing down on it.
This compresses the air, increasing its pressure and increasing its density.
This just means that, in the same amount of space, higher density air has more molecules
in it than lower density air.
So if you grabbed a cubic metres of air at Monza, which is only 162 metres above sea
level - that air would weight a robust 1.22 kg.
But if you went to the Mexico circuit and grabbed that same cubic metre of air it would
only weight 0.98 kg.
The air at Monza has 26% more “stuff” in it than the air at Mexico.
This leads us onto the interesting and often mentioned fact that, despite the fact that
Mexico runs very, very, aggressively high aero setup, and Monza runs very low, skinny-winged
aero setup - it’s the Monza package that produced more overall downforce.
So let’s look at aerodynamics then.
We’ve gone into much detail before about how downforce is generated but - put simply:
the more air the car can heave upwards, the more that air will push the car back down.
An equal and opposite reaction.
The car pushes air up, the air pushes the car down.
That’s why downforce increases as the car’s speed increases - it passes through more air
every second so it pushes more air up every second so the air pushes down harder on the
car every second.
Now, at higher altitudes, there’s a lot less air in the atmosphere.
In Mexico, as we learned, there’s about 26% fewer air molecules available to push
against so there’s less air available to push back.
So you can jack the wings right up but you’re just not going to capture the same downforce
levels as you can down below where the air was thick and heavy with molecules.
Incidentally, this is why helicopters can’t fly very well more than 3km above sea level.
There’s just not enough air for the helicopter blades to push against.
Aeroplanes, on the other hand - they too have a limit where the the air is too thin to lift
the plane.
But they run into trouble quite a bit below that ceiling.
An aeroplane’s altitude limit is where there simply isn’t enough oxygen in the air to
power the engines.
And this is the other major effect on the car’s at altitude.
The combustion engines will be gasping for air.
OK, so let’s revise how petrol engines work.
It’s a little bit of chemistry, but it’s all easy to follow.
Combustion engines work by burning fuel inside a piston chamber.
As you probably know from the ol’ Fire Triangle, to burn stuff you need Fuel, Heat, and Oxygen.
In the case of petrol combustion - the fuel is the petrol, which is hydrogen and carbon;
the heat comes from the spark ignition; and the oxygen is mixed into the fuel from the
air.
And in burning all this fuel with oxygen, everything rearranges and we get a bit of
water, some carbon dioxide and maybe carbon monoxide, and we get a bit of extra energy
left over which drives the engine.
That’s the basics of what’s going on chemically.
You need the oxygen being fed in with the fuel in order to feed this reaction otherwise
nothing useful will happen.
Now, there’s an ideal ratio for mixing oxygen with petrol and that’s about 14.7:1.
So for every 1 gram of petrol fed into the combustion chamber, you need 14.7 ish grams
of oxygen (or thereabouts).
That means everything gets burned efficiently with very little left over.
So, with a normally-aspirated engine - that is, an engine that breathes all its oxygen
from the airflow without any extra help, having less oxygen available in a thinner atmosphere
means you can feed less fuel into the engine which results in less power output from the
engine.
So, with 26% less oxygen in the atmosphere, engines in Mexico should produce around 26%
less power under normal conditions.
But - we don’t have normally aspirated engines anymore.
We have turbocharged engines.
And what turbos do is spin incredibly fast - normally about 8 times faster than the engine
itself - to pump air into the engine.
The more air you pump in, the more fuel you can pump in and the more power you get out
of the engine.
At these high altitudes, the teams have to really ramp up the turbo.
It now has to do a lot more work to try and get as much oxygen into the engine as it would
normally have.
So actually, the overall power isn’t dropped too much.
But the turbo is having to work about 10-15% faster, going from around 100,000 RPM to about
110, 115,000 RPM.
And that puts a lot of stress on the turbo.
And it adds a lot of heat, which is bad partly for reliability and partly because turbos
want to pump air as coolly as possible into the engine.
Unfortunately cooling is another thing set back from this curséd low density air.
Once on track, F1 cars are only allowed to be cooled by the relative fast moving airflow.
This air is channeled through ducts and air intakes to all the required places and expelled
out of the back of the car.
Air-cooling works by transferring heat from hot components to each molecule of air as
it moves past.
That molecule then carries the heat away from the car.
If there are fewer molecules available to carry the heat away then you won’t be able
to cool the car as well as you’d like.
This means overheating engines, turbos, electronics and brakes if you don’t prepare the car
properly.
So you’ll see cars that are a lot more ‘opened up’.
Massive brake ducts, air intakes maximised, more panels opened to allow air in and out
of the chassis.
All of this will shift which parts of the car are more important to overall performance.
If you’ve traditionally had an advantage with your Internal Combustion Engine then
that might not mean as much if you don’t have a powerful, robust turbocharger.
Mechanical grip will come heavily into play - the way your suspension and chassis body
transfers grip and balance to the car is basically unaffected by air density so if you’re Red
Bull and you’ve got this area of your car nailed then you’ll be rewarded when the
power units’ potency becomes less of a differentiating factor.
And finally, let’s not forget the driver.
Fun fact: drivers breathe air.
Why do drivers breathe air?
The same reason as you and me - to deliver oxygen to the muscles to produce energy!
If there’s less oxygen available then this means the muscles get less oxygen and there’s
less energy available for exerting yourself through motorsports.
The overall effect is having to put in more effort for the same output, which ends up
fairly tiring.
Most athletes who will need to compete at altitude will train at altitude for a while
ahead of time.
This makes the body produce more red blood cells which allow more passage of oxygen to
the muscles and brain and basically balances everything out.
But with only a week between races there simply isn’t the time for proper altitude acclimatisation
so the drivers have to - pardon the phrase - suck it up.
The next race is Brazil, the second highest race on the calendar where we used to hear
a lot of talk of the effects of thinner air on the engines.
But Brazil is “only” 800 metres above sea level and has only a 10% drop in air density
compared to Mexico’s 26% deficit.
It’ll be interesting to see if the unique performances between teams continues after
the cars descend 1.4km to Sao Paulo.
I wouldn’t hold your breath.
Q&A time!
I’ll always try and do one of these when I can.
Last week I was rushed for time because I was going to York.
You don’t care about that though.
Question 1!
Isn’t it Micheliiiiin?
Not Michelaaaaaan?
- OK I got a lot of comments on this vein.
Pronounce it how you like, everyone!
The french pronunciation is Michelin but Michelin is cool.
You can call it Mitchy-witchy-doobie-da if you like.
I’d dig that.
Question 2!
I was two.
You sure were, Jasper.
So was I, once.
Question 3!
Why have I just got the notification?
OK, I included this cause I get comments like this every so often.
As a YouTube viewer I don’t use the notification system but my understanding is that it’s…
unreliable and buggy as heck?
I’m sorry if the subs or notifications play up for you but I…
I don’t know how to fix that.
Question 4!
Please more story time with Chainbear!
I don’t normally shove praise-like stuff in here but I wanted to say that I really
liked doing US Grand Prix story time and I really want to do more episodes for other
past grands prix.
So expect a couple over the winter!
OK bye now!