Impact induced vehicle residual deformation serves as a basis for the reconstruction engineer to make a determination of the energy absorbed during the impact phase of a collision. Many impact phase reconstruction algorithms assume a linear relation between an absorbed energy function and residual crush in order to derive collision severity (Delta V, BEV, etc.). This is done through the assumption of a constant spring stiffness value to describe the vehicle frontal impact stiffness. However, some recent rigid barrier impact test data has demonstrated non-linear trends between crash energy and residual crush. The total body of available crash test data indicates that vehicle frontal stiffness cannot be precisely modeled through the use of a single linear spring stiffness for all vehicles. This paper will explore stiffness trends and make comparisons to the previously assigned linear assumption for a diverse sample of vehicles and test speeds into frontal fixed barriers. The available crash test data is plotted and analyzed and the resulting linear and non-linear trends are discussed. Applications to the accident reconstruction field are also explored.