Adjusting the tyre pressures brings the tyres into their optimum temperature range (75°-90°). It also allows you to adjust grip, wear level and top speed.
The basis :
The pressure recommended by the manufacturer Pirelli is 29 psi (about 2.0 bar), with a temperature range of 75° to 90°. Pirelli slightly overestimates the pressures, mainly because the tyres have to be suitable for cars of varying weight and also to avoid kickbacks.
In practice, the teams drive with slightly lower pressures. The more the tyres are inflated, the less friction there is between the tyre and the ground. Friction is the phenomenon that transforms speed into heat, which is the principle of the disc brake. This is also the reason why increasing the pressure increases the top speed. Be careful, the temperature of the brake discs also affects the temperature of the tyres, especially if the discs are overheated.
Tyre pressures can also be used to balance the level of grip between the front and rear of the car, as well as wear.
Rule of thumb :
- Decreasing the pressure increases the temperature.
- Increasing the temperature (by other means: pinch, aerodynamic load) increases pressure (see explanation below).
- Lower pressures: more grip (up to a certain point), less reactive and more predictable car, more wear (because more friction).
- Higher pressures: less grip, more responsive and less predictable car, less wear, more top speed
What about Motec telemetry?
The Motec will allow us to monitor the evolution of pressures and temperatures during the session. In particular, it is interesting to look where the maximums are reached, as well as to study in detail the places where the car is unstable to check that this does not come from temperatures or pressures that are too low or too high.
What if we don’t know the ideal pressure?
In theory, the ideal pressure is achieved when the inside, middle and outside of the tyre work equally well. How do you know this? Just look at their respective temperatures. If these parts work as much, they will have the same temperatures (the more it works, the hotter it gets). But beware, because of the camber, the inside will inevitably be warmer. So we will try to have a linear temperature distribution: 76° (int), 73° (middle), 70° (ext) is a good distribution, whereas 76°/75°/70° is not (the centre works too much, you have to lower the pressure).
What about the ideal temperature?
Only based on the driver feedback ! Impossible to use telemetry to determine ideal values. Ideal temperatures depend on the constitution of the compound. This is usually a parameter that the manufacturer provides. If this is not the case, you will have to try different temperatures to determine which works best.
WHY MORE HEAT GENERATES MORE PRESSURE ?
Overall, two opposing phenomena determins the behaviour of a tyre:
- PV = nRT (ideal gas law). This equation says that in a volume (a bottle, a tyre), if the pressure increases, the temperature also increases, and vice versa (if the temperature increases, the pressure also increases). Based on this equation, increasing the pressure should increase the temperature of the tyres.
- Except that if the pressure is lowered, the tyre will deform more, so there will be more friction with the ground, therefore more heat created, therefore more temperature. This is the most important phenomenon.