To provide a grip force variable tire capable of individually changing the grip force for every independent tire if necessary in interlock with brake pedal operation amount, the amount of rainfall and steering amount when a car, a motorcycle or the like requires a strong grip force or a light grip force, e.i. when a brake is applied, when it starts raining, when the car, motorcycle or the like travels a curve or the like.

A plurality of pipes (2) are passed from a grounding face (1), a peripheral surface of the tire in contact with a road surface to a side surface (3). Valves are attached to the pipes and the grip force is varied relative to the road surface of the vehicle by injecting wind and rain to the grounding face of the tire, the road surface (1) or the side surface (3). The side surfaces (3) of the respective tires are covered (10) to prevent air and water from escaping and wind and rain 6 is made to blow more violently through the pipes (2) inside the tire (4) by naturally caused wind or wind (6) caused by a motor fin (14), and a grip force for every tire (4) is individually varied to enhance the effect.