A turn plate assembly for support of the steered wheels of a vehicle on a precision planar surface. The assembly includes an approach plate establishing a planar surface to within an established measurement tolerance. The approach plate is coupled to a base plate underlying a bearing assembly consisting of a plurality of ball bearings retained between the base plate and an underside of a rotating support disc. An upper surface of the rotating support disc is coplanar with an upper surface of the approach plate. Resting on the upper surface of the rotating support surface, a translational surface or mat is temporarily secured in place by magnetic adhesion. During use, translational forces exerted on the translation surface or mat by a vehicle wheel assembly may overcome the magnetic adhesion, enabling the translational surface or mat to translate relative to the underlying rotating support disc.