In prior art wheel balancing instruments of the suspended type, it has been a time consuming operation to mount the wheel thereon in centered relationship, since the manual adjustment of parts has been necessary. Thus, in U.S. Pat. Nos. 2,481,256 to Sutton and 2,512,231 to Hart, wherein oppositely facing wheel center engaging parts are provided threadably mounted on a central shaft, it is necessary to manually move these parts to tightly grip the wheel center. Also, in U.S. Pat. No. 3,452,605 to Markley, where a conical member is provided for insertion through the center of a wheel, it is necessary to adjust a plurality of wheel supporting nuts mounted on the conical member.
Further, since prior art wheel balancing instruments have not had a feature permitting sensitivity adjustment during the balancing operation, there has been a tendency for parts of the instrument to be initially subject to high deforming stresses.