Vertical stiffness and damping coefficient values were measured, in non-rolling conditions, on eleven agricultural drive tires, with sizes ranging from 14.9-30 to 18.4-38, and both types of carcass construction, bias and radial, were tested. Tire stiffness was measured both in static and dynamic conditions. The mechanical model representing the tires was made of a parallel spring-and-damper system, simplified to a single spring in static conditions. Tire stiffness was linearly related to inflation pressure in all cases, but dynamic stiffness was higher than static stiffness. The use of different tire models for static and dynamic conditions is recommended during simulation and tire behavior prediction.