This paper examines the validity of the effective mass concept used in the CRASH 3 damage analysis equations. In this study, the effective mass concept is described, the simplifying assumptions that it entails are detailed, and the accuracy of the concept is tested by comparing ΔVs calculated from the CRASH 3 equations to results of numerical simulations with a non-central impact model. This non-central impact model allowed the effective mass concept to be tested in isolation from other assumptions of the CRASH 3 program. The results of this research have shown that the effective mass concept accurately models the effects of collision force offset when certain conditions are met. These conditions are discussed, along with their implications for damage interpretation.This paper also presents an analytic expression that relates damage energy to closing speed (initial relative velocity) for the general case of non-central collisions. Equations relating damage energy to closing speed for the case of central collisions have been discussed extensively in the literature. However, a comparable equation for the general case of vehicle-to-vehicle non-central impacts has not been reported. The effective mass concept is used to generalize the relationship between closing speed and damage energy.