Measuring vehicle front end parameters

Apparatus for dynamically measuring vehicle wheel alignment parameters, said apparatus including support means for supporting a vehicle wheel and causing rotation thereof, and a sensing roller adapted for contact with the tire tread surface of a tire on said wheel to be rotated by said rotation of the wheel, said sensing roller being arranged at the lowermost point of said tire and on an axis of rotation extending transverse of the plane of rotation of said wheel whereby any toe-in or toe-out of said wheel causes, during rotation, a displacement of said sensing roller in said transverse direction to a position indicative of said toe-in or toe-out, and said sensing roller being mounted to pivot, according to said displacement, with respect to a pivot point located substantially co-planar with the plane of said wheel, in the true forward direction of said wheel and a substantial distance away from said roller, and in a position whereby said sensing roller trails said pivot point with respect to the direction of rotation of said wheel, means structurally related to the sensing roller to measure said displacement, for the purpose of computing toe-in or toe-out and said sensing roller being mounted for rotation on an axle forming one bar of a trapezium shaped four bar linkage constituting a pivoting system to facilitate said displacement, all the bars of said linkage being pivotally interconnected and said pivot point being defined by an imaginary point at which center-lines of the tapered members of said trapezium shaped linkage intersect.