The effect of specimen’s mean radius to average wall-thickness ratio rs/t, has been studied using the Split Hopkinson Torsional Bar. The rs/t ratio was varied between 6.5 and 39 keeping the outer diameter and the gauge length of the specimen constant. Higher strain rates and strains are observed for specimens with larger specimen radius to wall-thickness ratio rs/t. However no monotonic trend of the shear stress with rs/t variation is found. A sharp decrease in the torsional stiffness of the specimen is observed with increasing the specimen’s rs/t ratio. The rs/t ratio can also be used as a useful dimension to enhance the strain rate in tubular specimens.