Typically the roll propensity of a vehicle is calculated from the assumption that the vehicle is a rigid body and that its roll propensity can be determined by taking the ratio of the track width and the center of gravity height. However, a passenger vehicle is not a rigid body; it is at least two rigid bodies connected through links and springs and shock absorbers. The objective of this paper is to derive a new second order rollover metric, which will predict whether a vehicle may be susceptible to rollover from simple physical measurements of the vehicle. The validation of the derived metric using a stock and modified vehicle configuration will be presented. Further validation with several vehicles is planned and will be reported in later papers.