Abstract
The theory of flatspotting in tires is reviewed and found to be in essential agreement with that given in earlier publications. The importance of cord moisture content (humidity), temperature, and dynamic response rate in affecting the flatspotting per formance of tirecords is emphasized. Two methods are discussed for favorably altering the viscosity-temperature relationship of nylon tirecords: (a) incorporation of moleculea of bulky groups along the polymer chains (achieved through blending with other poly mers), and (b) plasticization. A new, dynamic flatspot cord testing machine is described which permits close simulation of tirecord stress cycles that duplicate the flatspotting phenomena under various cord moisture contents (humidity test atmospheres) corre sponding to both summer and winter driving conditions. Good correlation is obtained between the laboratory test results and tire results. Applications of the test machine in screening prospective low flatspotting tirecord materials is discussed.
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