A machine vision vehicle wheel alignment system optical target assembly which incorporates an adaptor for attachment of an optical target to a vehicle wheel assembly. The adaptor includes a circular sinusoidal edge for seating in a non-determined position against surfaces of a vehicle wheel assembly, and a pair of pivoting arm assemblies capable of independent movement which are configured to position tire hooks for gripping the tread surfaces of a tire mounted to the wheel rim. Forces exerted between the pivoting arms are transferred to the tire hooks to hold the optical target assembly in contact with the wheel assembly surface. The optical target is integrated into the adaptor, and maintained in a stationary relationship to the wheel assembly thereby during a vehicle wheel alignment procedure.