Changing tyre pressures is one of the first adjustments that you usually make to a car, as the tyre contact patch defines how much grip is available to the car. In order to understand how tyre pressures affect the grip of the car, we need to dive into the physics of the tyre.
Under, Normal and Over Inflation
Race cars need to use the maximum amount of grip that is available from the tyres. To achieve that we need the maximum contact patch (the amount of surface area of the tyre that is touching the track surface) with the track surface.
Therefore, we tend to have as low tyre pressures as possible to maximize the contact patch. However, there’s a catch: having too low tyre pressures will cause the side of the tyre to bend resulting in loss of grip during the corner.
Having higher tyre pressures has its benefits as well. As the contact patch is less, we can achieve higher top end speeds because there is less friction between the tyre and the track surface. This is great until we get to a corner. Due to the lower contact patch, the amount of grip available from the tyres is less, therefore, the corner speed is lower as well.
In order to find the balance between low and high tyre pressures, we need to head out on the track for some testing. Start by doing 8-10 clean and consistent laps with the baseline setup tyre pressures. This will give you a feel on how the car behaves during cornering. After you complete the laps you can make small adjustments to improve the car according to how it behaved with the baseline tyre pressures. Below you can find some information on what adjustments to make based on the issues you experience.
Keep in mind that finding the balance of the tyre pressures depends on the load that the tyres carry. For example, in a high speed corner more grip will be available when using higher tyre pressures as they handle higher loads better since the sidewall of the tyre is stiffer. In a low speed corner, more grip will be available when using lower tyre pressures as the tyre load is less and the contact patch is more.
iRacing’s Skip Barber F2000 is always fastest using the minimum tyre pressures available.