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Summary form only given, as follows. Many drives with either 3.5-in or 5.25-in disks operate without any position feedback mechanism and required that materials used within the drive have carefully controlled coefficients of thermal expansion. Completely eliminating thermal offtrack by simply selecting from available materials is often not possible. A method of fine-tuning the offtrack is presented. The method involves adjusting the relative thickness of materials used in a bimetallic composite structure to provide the expansion desired. A computer model predicts results within the drive and a comparison is made of analytic and experimental results. In addition, an overview of the causes of offtrack under both thermal transient and steady-state conditions is presented.