Mechanism of Tire Flatspotting and Its Relation to Fiber Properties

Abstract Tire flatspotting has been shown to be related to cord compression in the footprint area. Because of compression, the cords are under less tension than those cords outside this area, and contract. Cord contraction and the depth of a flatspot which develops in a tire depend on: 1. Cord Physical Properties: Modulus dependence on temperature, Tg, crystallinity and orientation; response to applied stresses, and creep. 2. Tire Design Factors: size, number of plies, cord angle, cord construction (linear density and helix angle). In order to exhibit low flatspotting, a tire yarn must meet the following physical property requirements: high immediate elastic region—high modulus, high glass transition temperature—low creep, high yield point, high intermolecular chain friction (H-bonding, crystallinity) and low moisture regain.