A tire for agricultural vehicles has to satisfy several contrasting requirements. As first it has to provide high traction forces, maximizing traction efficiency; i.e. longitudinal forces should be developed with low slippages. Secondly, the tire should be able to limit the vibrations induced by soil/road interaction improving riding comfort. As last, soil compaction should be minimized, so that roots development will not be affected by the passage of the agricultural vehicle. Lowering tire pressure emphasizes the effect of tire deformation; in particular the contact patch gets longer and thus the number of lugs simultaneously in contact with the ground increases. This clearly affects the distribution of normal and tangential contact stresses acting on each lug influencing global contact forces and soil compaction. Thus, the effect of tire flexibility has to be introduced. A modal superposition approach was used to include the deformation of the tire. For this purpose an experimental campaign was carried out to identify the in-plane eigenmodes of agricultural tires. Two agricultural tires with different size and lugs number were instrumented with 8 accelerometers glued along the external circumference. Several impulsive tests were performed by means of a dynamometric hammer. The impulse responses were then analyzed in the frequency domain to extract modal parameters, i.e. eigenfrequencies, eigenmodes, damping ratio and modal mass. Eigenmodes in the range 25-80 Hz were identified for two different inflating pressures.