It is well known that a tire lateral stiffness influences vehicle dynamics. But a lateral stiffness in service condition has not been measured until now. So tire construction designers use a lateral stiffness measured at a static condition as common sense. In this paper, a lateral stiffness in service condition (rotating at high speed) was measured with non-contact shape measurement method. In addition to it, a lateral stiffness variation corresponding to the trapezoidal slip angle input was

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... sured. From this result, we understood that a lateral stiffness of a rotating tire can not be treated as a linear characteristic.