Wheel balancer with means for determining tyre uniformity

A method for determining tyre uniformity of a rim/tyre assembly including a tyre and a rim mounted on a measuring shaft of a wheel balancer adapted to measure forces resulting from an unbalance of the rotating rim/tyre assembly, the method comprising the steps:

• rotating the rim/tyre assembly about a shaft axis of the measuring shaft and applying a predetermined force to contact portions at which the periphery of the rim/tire assembly contacts a load device in different angular positions about the shaft axis, wherein
• during the rotation, the measuring shaft and the load device are strained to one another by the applied predetermined load and forces acting in the contact portions in the different angular positions about the shaft axis, and the load device and the shaft axis are kept in stationary positions;
• measuring the forces acting in the contact portions of a periphery of the rim/tyre assembly in the different angular positions;
• measuring a runout of the rim/tyre assembly and a runout of the bead seat surfaces of the rim;
• comparing a measured force variation measured in loaded condition through 360° of rotation angle with a calculated force variation which depends on the measured runout of the rim and of the rim/tyre assembly, and on an average tyre stiffness associated to a specific tyre design or tyre type;
• and
• varying the value of the average tyre stiffness in the calculated force variation until best matching of the measured and the calculated force variations is achieved to determine within 360° a local angular position of at least one difference between the measured and the calculated force variation.