[Uniformity] What is Tire Uniformity?

What is Tire Uniformity, or actually Non-Uniformity?


It is a quantitative measure of force and runout variation within a tire.


The primary parameter measured is Radial Force Variation. Radial Force Variation is a property of a tire that characterizes the dynamic behavior of forces generated (such as steering, traction, braking, and load support) between a vehicle and the road surface. As the tire rotates, the spring elements of the tire make contact with the road surface and are compressed. As each individual spring element rotates out of the contact area it recovers to its original length. Variations in the effective stiffness of each of these spring elements result in radial force variation. The change in effective stiffness and therefore forces generated is due to variation in the thickness of the tire and variation in the elastomeric properties of the tire.


Under the same conditions, if the same load is applied at a constant radius to a rotating tire, it will generate a lateral force and a Lateral Force Variation. As the tire turns, it undergoes repeated deformation and recovery as it enters and exits the contact area. If thelateral force is measured between the tire and the road surface the lateral force will vary as the tire turns. The average value of this generated lateral force is called Lateral Shift. Lateral Force Variation is the small amount of variation in lateral force around the lateral shift. The change in these forces is due to inconsistencies in the tire tread and sidewall area.


Force variation refers to the change in the force as the tire rotates along the surface of the road, providing the center of the tire remains at a constant height above the surface of the road. There must be a load on the tire to generate any force variation.


The Free Radius of a tire is defined as the average radius of the inflated tire from the rotational center of the tire to the tread surface. Tire Runout variation is the variation measured around the free radius.