Radial force variation
Open-knowledge reference entry

Radial force variation or road force variation (RFV) is a property of a tire that affects steering, traction, braking and load support. High values of RFV for a given tire reflect a high level of manufacturing variations in the tire structure that will impart ride disturbances into the vehicle in the vertical direction. RFV is measured according to processes specified by the ASTM International in ASTM F1806 – Standard Practice for Tire Testing.
Explanation
RFV can best be explained by example. Assume a perfectly uniform tire mounted on a perfectly round wheel loaded with a constant force against a perfectly round test wheel. As the wheel turns, it turns the tire, and the tire carcass undergoes repeated deformation and recovery as it enters and exits the contact area. If we measure the radial force between the tire and the wheel we will see zero change as the tire turns. If we now test a typical production tire we will see the radial force vary as the tire turns. This variation will be induced by two primary mechanisms, variation in the thickness of the tire, and variation in the elastomeric properties of the tire.
Consider a good tire with RFV of 6 pounds (27 N).
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