A gauge for use in a wheel balancing machine for ascertaining the location of the plane of the inner edge of the wheel rim. The gauge includes a flat resiliently flexible plate which has an edge that is graduated in units of distance. Extending from the plate remote from the edge is a support bar and there is means for mounting the support bar for slidable movement along its longitudinal axis to permit positioning of the graduated edge adjacent to the inner edge of the wheel rim so that the position of the rim can be ascertained by comparing its location with that of the graduations.