Summary: We consider air contained in a pneumatic tyre with the purpose of investigating its inertial oscillations. We model the tyre as a torus limited by a membrane in contact with the ground. According to this model, we prove that the flow within this torus may be considered as oscillations of incompressible rotating fluid at low Mach number. Then we show that the geostrophic oscillation is resonant, and we study this resonance phenomenon.