In our latest technical feature, Seb Scott explains the reasons why the Autodromo Hermanos Rodriguez produced such high top speeds. _
The Mexican Grand Prix was an odd race, wasn’t it? Rosberg won, Hamilton didn’t, Ferrari had a double DNF, the podium wasn’t anywhere near the pit-lane and wing angles were the same as at Monaco.
However, the biggest difference for the eagle eyed amongst us was the fact the cars were running steep wing angles on a day where the highest top speed of the season was reached – 366km/h (227.4mph) by Sebastian Vettel in his Ferrari.
This posed a couple of questions. Why couldn’t the cars go anywhere near that speed at Monza, where they ran a much more subtle wing angle and, why was it possible to achieve such high speeds with conservative downforce levels? The answer is the same reason as why jumbo jets fly at such a high altitude – the air is thinner at higher altitudes.
Although air cannot be seen, it is still a very present thing and a mammoth factor for Formula One teams to over come, one that most are expert at maipulating. An interesting fact for you – when air is at sea level and room temperature, a cubic metre of air weighs more than a standard bag of sugar. This is because the air’s density is directly related to its pressure and temperature; the closer to sea level you are, the higher the pressure and therefore density. The meaning of density is mass per volume, so essentially there’s more air per cubic metre at sea level than there is at the summit of Mount Everest. Standing at the top of said mountain, a regular person would need an oxygen tank to breathe normally, unless the person has adjusted to high altitudes and put in a hefty amount of training.
This lack of air due to altitude also affects vehicle performance, particularly on the engine. An engine, just like a human except combined with petrol, needs air to function effectively and it needs a lot of it. The thin air means a car has less air forced into the combustion chamber (where the fuel and air are mixed and ignited by a spark), and so less power is produced. All 2015 cars now run a turbocharger, one of the main objectives of which is to compress air intake to a higher pressure and achieve more power given the same amount of fuel. This meant, although teams expected to have a loss of power during the Mexican Grand Prix, it was alleviated by the fact they could run their turbos a lot higher and at a higher relative pressure than normal.
No solution, it seems, could be found for the cars aero though, as it soon became apparent last weekend that the cars didn’t have enough grip on circuit, thanks to the lack of downforce. As mentioned previously, air is thinner the higher the altitude and, as the name states, aerodynamics very much rely on the properties and relative movement of air to a Formula One car in order to allow them to generate downforce. Even though the wing angles demonstrated by teams appeared to have high angles of attack and looked to induce a lot of unnecessary drag given the circuit layout, they in fact generated less than the types of wings used at Monza.
This is due to the air density at the 2200 metre altitude of Mexico City. Wings had a weaker effect and so had to be ran at higher angles of attack to eke out any extra performance that was available to them, a task made more complex by the fact the airflow at Autódromo Hermanos Rodríguez was less adhesive than normal and so was harder to maintain and control. The air pressure was around 20% less than in normal conditions. To give some idea of how much downforce that would remove from the cars, the current Manor generates only a couple of percentage points less downforce than most of the current F1 field and is considerably off pace.
Mechanical grip wasn’t even available for drivers this weekend, due to the slick asphalt, and yet top speeds were the highest they’ve been all season. This was because of the same reason the drivers were complaining about a lack of grip; the air was so thin, there was less drag meaning less forces were opposing cars during acceleration so they could achieve higher speeds at a much faster rate. Think about if you have one person swimming in a pool of syrup and the other in water. If you set out a very tight, narrow, twisty course, the person in the syrup pool would be able to navigate with a lot more confidence and effect than the person in the water due to the amount of relative grip the thick syrup would provide. Yet if you had an out and out lane race, the person in the water would beat our imaginary syrup swimmer hands down, thanks to the lack of resistance and more slippery characteristics of water.