Abstract: A device for determining the radial displacement of a motor vehicle relative to the overall direction-of-track of same, said device comprising a swing arm; a tire/wheel assembly which is operatively disposed upon one end of said swing arm and is provided to facilitate tractive rolling engagement of said swing arm with a road surface; a spring-loaded pivot assembly secured to substantially the end of said swing arm opposite of said tire/wheel assembly; and a rotatably free kingpin which is secured to said swing arm through said spring-loaded pivot in such manner as to provide a radial reference for said spring-loaded pivot to facilitate the forcing of said tire/wheel assembly onto said road surface for the purpose of tractively following any perturbations existant thereon.