A method and apparatus for continuously measuring the lateral spring rate of a rotating tire. A tire is mounted on a rotatable tire support and urged against an anvil means which is mounted for rectilinear movement relative to a fixed support and in a line parallel to the rotational axis of the tire. Drive means are provided for rotating the tire and imparting the rectilinear motion to the anvil. Means are also provided for measuring the rectilinear movement and the force required to impart the movement. The foregoing abstract is not to be limiting the invention of this application, and in order to understand the full nature and extent of the technical disclosure of this application, reference must be made to the accompanying drawings and the following detailed description.