Patent ID: 7971477

Claim:
A detection method for at least one of acting forces on a tire among a back-and-forth directional force, a lateral force, a vertical force, and a moment about a tire axis, to detect by strain outputs of strain sensors, which are attached on the tire and measure the strains of a sidewall portion, wherein said strain sensors comprise: first strain sensors that have the gain maximum line, in which the gain thereof becomes max, inclining to one side of the circumferential direction of the tire at an angle of 45 deg. with respect to the tire radial direction line, second strain sensors that have the gain maximum line inclining to the other side of the circumferential direction of the tire at an angle of 45 deg. with respect to the tire radial direction line and at least four pairs of sensors, in which one of said first strain sensors and one of said second strain sensors are made a pair, arranged at regular intervals on the circumference line of one circle around the axis of the tire in the region of the sidewall portion of tire; and said method comprises: a strain measuring step to measure the strain of the sidewall portion with each of said strain sensors simultaneously on the rotational position P based on the tire rotational standard position X and to obtain the strain output per strain sensor, and an acting force calculating step to calculate said force acting on tire based on the strain output per strain sensor obtained on the strain measuring step; and wherein around the tire axis, polar coordinates that a perpendicular line extending upward from the tire axis is set to zero deg. and that a direction contrary to the tire rotational direction is set as a positive direction are defined; and said acting force calculating step is a step to calculate the back-and-forth directional force at said tire rotational position P based on a difference (Σtr−Σtf) between the summation Σtr of the strain outputs (tr) of the strain sensors positioned in a rear side region Yr in the tire rolling direction at a coordinate angle ranging from more than zero deg. to less than 180 deg. in said pole coordinate and the summation Σtf of the strain outputs (tf) of the strain sensors positioned in a front side region Yf in the tire rolling direction at a coordinate angle ranging from more than 180 deg. to less than 360 deg.