In order to investigate the effects of storage and service on passenger car tire performance, two separate sets of samples were characterized: (i) tires stored at a temperature of 45–50 °C for different time periods, and (ii) used tires of different mileage. The tires were analyzed with respect to the performance of the tread rubber as manifested in the modulus at 200% elongation, the tensile strength at break, the elongation at break, the hardness, the viscoelasticity of the rubber, swelling, and the oil component content. The change in the properties of the tires as functions of increasing storage time and mileage indicated a marked deterioration in performance. The rate of change in these properties was found to be markedly enhanced by the extra stimuli provided by service, as demonstrated by comparing tires of similar age but different mileage. The results were analyzed and rationalized in terms of the change in the degree of crosslinking and transfer of oil components from the tread rubber to the inner part of the tire or to the surroundings.