This paper presents the evaluation of the optimum mixing ratio of sand-tire chips (STC) mixtures based on void ratio and shearstrength properties. Locally available sand and tire chips of 20×10 mm size are adopted. Different STC mixtures, in the range 10-70% by weight of tire chips (TC), are considered, along with pure sand (0% TC) and pure tire chips (100% TC). Specific gravity, density, and large direct shear tests were conducted for various samples. The volume of voids and weight-volume relations were determined from the dry unit weight and specific gravity values obtained for various mixtures. The results showed that the addition of tire chips up to 40% by weight showed significant decrease of void ratio by 43%. Shear-strength properties, like angle of internal friction values, are increased with TC contents up to 30%. Based on experimental results, the optimum percentage of tire chips of the selected size is in the range of 30-40% by weight, which is the equivalent of 50-60% by volume. Further, the STC mixture at the optimum ratio results in lightweight material with 20% less unit weight with better strength parameters and compressibility behavior, which can effectively be used for geoengineering applications. © 2015 American Society of Civil Engineers.