The qualifying preparation lap is becoming an aspect that can increasingly have an influence on performance. The topic has become very topical after Charles Leclerc's difficulties in expressing the full potential of the SF-24 in the flying lap became apparent, he who has always been appreciated for his extraordinary ability to exploit the material he had available.
Moving away from the specific case of the Ferrari driver, it seems right to try to understand why it became so complicated to get the tires to the right temperature for the qualifying lap.
And so, the idea was born to ask Pirelli, the sole supplier of F1 tyres, for an understanding of how this delicate topic can be addressed by the teams. Mario Isola, head of Pirelli Motorsport, was available to explain to us in a simple and informative way the versatility of a problem that is not easy to solve even for the team engineers.
Mario Isola, head of Pirelli Motorsport
Photo by: Mark Sutton / Motorsport Images
Before going into the detail of the out lap, a more general premise must be made, introducing the concept of the working range of an F1 tyre. How is the usage window of a tire measured?
“In a Cartesian graph – explains Isola – we report the grip of the tire on the ordinates and the temperatures produced on the abscissas. Any compound developed for cold motorsport develops little grip. The grip value increases as the temperature increases: you will observe a curve that will grow until reaching a peak, beyond which there will be a significant drop in grip due to overheating”.
Therefore, we will have a different design curve for each of the five compounds approved for F1. But how is the working range found?
“Once the peak of grip has been reached, at the highest point of the curve, the graph conventionally drops by 3% to find what we define as working range: it is a line between two points that we try to make flatter, but, above all, as wide as possible.”
“Our goal – adds Isola – is to give the riders the tire with the wider plateau, to ensure them a more open operating window. In the graph you can see that the working range varies depending on the more or less soft compound and other parameters which we will then analyze later”.
Behavior of the tires in the race with a compound that is not the soft one
Photo by: Gianluca D'Alessandro
In our graph we start from the cold tyre, while in F1 to facilitate use the tires are pre-heated in the thermo-tyres to a maximum temperature of 70 degrees (set by regulation by the FIA). The drivers, therefore, leaving the pit lane, will find themselves with a tire already capable of ensuring a minimum grip value. It may seem strange, but there are teams who, suffering from endemic overheating in the qualifying lap, have also tried to reduce the temperature on the heated blanket. It should not surprise us, therefore, how the effect of the preparation for the loop transfers to phases that precede entry onto the track, in the attempt to find the best way to manage the tire according to one's single-seater.
We understood that each compound reaches a different grip peak, drawing a curve on the graph that is never the same, so even the line that determines the working range can be more or less wide and with quite different use temperatures. It should not be surprising, therefore, if we observe F1 who are fast with one compound and are much less so with another.
To summarize, can we say that there is a window of use for each compound?
“Yes and in the past we had also made this information public. We have no longer done this because the tire usage windows are highly influenced by a series of parameters that can significantly modify the data: we can start from the type of asphalt, up to the suspension set-up adjustments. We must not forget that there is a mechanical component of grip and an adhesive one, so there are cars that stress the tires in very different ways.”
During long runs and race stints, the drivers try not to go outside the tire usage window with the aim of obtaining maximum performance and minimal wear, limiting degradation. If, however, the qualification is prepared, the approach changes completely: the working range counts for less than zero and other parameters are sought.
Which?
“The answer is simple – insists Isola – during the flying lap the driver tries to get as close as possible to peak grip, avoiding causing the tire to overheat. We are therefore going to act in a very narrow field, because we try to eliminate the 3% deviation that exists between the working range line and the peak grip”.
Tire behavior in qualifying with the soft compound
Photo by: Gianluca D'Alessandro
Why is it becoming so important today to exploit that 3% more grip in the flying lap?
“The reason is given by the competitiveness of current Formula 1. We have a grid of 20 cars which is sometimes assembled in just over a second. In the past we have experienced seasons in which the top positions were played with margins of two or three tenths per lap and, then, it was possible to work around the working range line, while with such selective competition, where everyone is very close, divided from hundredths of a second, it becomes essential to reach peak grip: this is the secret to look for in qualifying.”
Another element that complicates the search for peak grip in qualifying is the lack of what is called balance…
“The front and rear axles do not work in the same way – continues Isola – and, therefore, temperature trigger strategies must be studied to find what is defined as the good balance before the finish line”.
The rear tires subjected to traction reach peak grip more easily, while the front ones struggle more to be ready. Here's another reason why out lap becomes important:
“The teams study their strategies to get to the flying lap – adds Mario – but it's not a given that what works on one car will also work on another”.
And then it becomes interesting to understand how the right thermal energy can be triggered on the tires. Basically there are three ways to act:
- by contact with asphalt
- due to deformation of the carcass
- with braking.
In the first case, surface heat is generated on the tread as a result of rolling: the rear tires heat up during traction during acceleration, while the front ones during braking.
With the deformation of the carcass, however, it is possible to increase the temperature in the tire structure, working on the balk, the heart of the rubber. And then the lateral forces that act in high-speed corners and the aerodynamic load are needed.
At low speed you can use braking to generate heat on the tyre: there are drivers who, depending on need, move the transfer case from the front to the rear and vice versa. With the 13-inch tires there was also a tendency to heat up the rims by radiating heat from the calipers and rotors to transfer to the tires. With the ground effect single-seaters, however, which adopt 18-inch wheels, the philosophy is to try to extract the temperature from the corner, so we have seen double carbon baskets appear inside which we try to circulate fresh air, precisely to avoid overheating.
Tire behavior comparison between qualification and race with different compounds
Photo by: Gianluca D'Alessandro
It is becoming increasingly clear why the qualifying preparation lap is so important. But there are also other conditioning elements that should not be overlooked: the layout of the slopes…
“Theoretically the driver looks for ways to get to the start of the flying lap with the front and rear at peak grip – continues Isola -. But this is not always the case: there are circuits where it is better to start the lap with the rear end which is not yet ready. The clarifying example is given by Barcelona. When you get to the third sector, the driven one, you need traction. If the tire has been used too hard previously, the rear overheats, losing a lot of grip and, therefore, performance. It is important to know how to manage the first two sections, to find a good balance. All it takes is to go out of the window by about ten degrees to lose the peak grip and pay a toll on the lap time.”
“The reading of the race, however, changes because there is the increase in weight due to the full tank of fuel (up to 110 kg). It is unthinkable to stay at peak grip, but we try to get down to the working range which is what is needed to manage the stint. What is the risk? If you go too high with temperatures in the race pace you end up overheating and then performance drops. The teams take care of this aspect: they work to avoid overheating and stay in the right window.”
F1 returns to China after five years, on a track with particular characteristics…
“The Shanghai layout puts the front left in serious difficulty because there is that very long Turn 1 that almost goes backwards, where the tire might not be ready yet because a lot of energy is required. At that point you have to be very careful not to trigger graining: it is easy for it to appear with a compound that is not yet up to temperature and, therefore, is mechanically weak.”
“In qualifying, graining leads to a reduction in performance. In the race, however, it is easier to manage it because during the stint it is a phenomenon that tends to disappear. Shanghai could offer us some particular situations because it won't be hot and in the cold it's difficult to maintain the tire temperature, given that there are two long straights.”
Isola gives another example and talks to us about Baku, the street circuit with a fast section longer than a couple of kilometres…
“What happens is that the air cools the tire on a straight line. It is true that the temperature is reduced on the surface and not in the balk of the compound, but when braking reaches the end of the straight, the rider finds himself with less grip. In Baku we recorded a 30 degree drop between the start of the straight and the end. And the pilot must be aware of these variations so as not to have to deal with surprises. The same problem could occur over the weekend in Shanghai if it is cool…”.
It should not be surprising, therefore, if the teams have equipped the machines with temperature sensors to collect the maximum amount of useful information…
“What we would like is the temperature of the balk of the compound – says Isola -, i.e. the heart of the rubber, but we don't have tools capable of doing this. And then you point an infrared sensor at the carcass which can somehow tell you what the sensitivity of the balk is. If the surface temperature can change a lot with the exposure of the tread to air, traction and braking, that of the balk has a little more inertia and better identifies how the compound is working”.
There remains a question to be clarified: where does overeating occur?
“Especially on the surface. And on this topic there is another aspect that should not be overlooked: the sensors try to brush the entire tread, because temperatures vary greatly from point to point. Based on the setup and how the suspension works, a range of temperatures that is as homogeneous as possible is sought. We have noticed that there can be variations between one car and another on the grid which run at different camber angles.”
To facilitate research and development, give the teams the model of your tire every year: what information does it contain?
“All the ones we have talked about so far, because it is a thermo-mechanical model that defines the grip of the compound as the temperature varies. When teams connect our virtual tire to their simulator, in theory the virtual tire should perform exactly like the real one. We have results that are now very close to reality. There is a very high degree of reliability.”
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