Trace and residue evidence is commonly collected at crime scenes and submitted to the laboratory for analysis with the intention of linking a perpetrator to a particular crime. Although a significant amount of time and effort has been put into capturing vehicle tire tread patterns, little research has been published on the characterization of individual tire compositions. Tire manufacturing is a complex process, and the final product is made from of a variety of different ingredients, with rubber being the most abundant constituent (Bodziak, 2008;Williams & Besler, 1995) The three most common rubber components are natural rubber (NR), 1,3-butadiene (BR), and styrene-butadiene (SBR), with most every tire containing a combination of some or all of these materials (Ding & Liu, 1989; Sarkissian, 2007). Microscale sealed vessel pyrolysis-gas chromatography-isotope ratio mass spectrometry (MSSV-Py-GC/IRMS) can be utilized to separate and identify components of tires. The purpose of this project is to determine the variability in polymer composition among brands of tires, different product lines from these brands, and from different locations on a single tire.