Property changes of TBR tire parts used in the practical field were characterized by means of log λ_b vs. log M₁₀₀ mapping method, which was found to be useful in classification of aging patterns obtained by laboratory oven aging into the Types I ~ III. The aging conditions in tires, those brought about Type I aging pattern, were considered to agree with those found in the laboratory aging tests. The property changes were brought about by crosslinking reaction at relatively lower temperature in the presence of oxygen. Type II and III aging patterns were also observed in the aged tire after the field use. These variations of the aging patterns were generated by diffusion-limited oxidation under the high temperature condition and the mechano-chemical reactions due to the mechanical impact or large deformation of rolling tires.