Vehicle stiffness is a commonly used parameter in the field of vehicle safety. But a single-valued “stiffness”, although well defined for the linear case, is not well defined for non-linear systems, such as vehicle crashes. Moreover, the relationship between vehicle stiffness and mass remains confusing. One previous work [1] addresses this issue. Multiple definitions of stiffness were used to address the lack of a clear definition of stiffness. The R2 values for the correlation between mass and each stiffness measure were presented. The results showed that no clear relationship existed between mass and any of the stiffness measures. The results from a statistical analysis indicated that there were differences in stiffness between different types of vehicles.

This paper extends the same research by including a significant amount of new data samples as well as some different analysis procedures. Results show that mass is poorly correlated to stiffness and for some vehicle types mass correlates better to vehicle crush than to stiffness. In addition, it is shown that even without a well-defined definition of stiffness different levels of stiffness can be defined and differences in stiffness between different vehicle types can be quantitatively and qualitatively established.