To improve travel performance by controlling deformations of sidewall parts of a tire in traveling.

This vehicle system includes a pneumatic tire for arranging polymer actuators in the sidewall parts, respectively, and a control means of the polymer actuators. The polymer actuator is formed in a sheet shape of joining a first electrode layer and a second electrode layer to one and the another surfaces of a polymer film. Deformation force in the direction for curving toward one surface side or the another surface side, is caused in the polymer actuator by controlling a voltage impression between the first and second electrode layers by the control means, and thereby, deformation of the sidewall part can be changed.