A frame assembly for a motor vehicle and method of manufacturing the same. The method includes the steps of: forming a rearward frame module, forming a forward frame module, and forming a central frame module including a pair of longitudinal central frame siderails. Each of the central frame siderails are constructed by 1) forming a sheet of metallic material into a longitudinal member having a generally U-shaped transverse cross section including a base portion and a pair of leg portions, 2) engaging opposite longitudinal ends of the longitudinal member and pulling the longitudinal ends in opposite directions with respect to the longitudinal extent of the longitudinal member in order to stretch the longitudinal member so that the metallic material forming the longitudinal member reaches its yield state; and 3) bending the longitudinal member having the U-shaped cross-section at two longitudinally spaced locations so that 1) at a first of the locations a) the base portion is bent generally within its plane, b) one of the leg portions is stretched, and c) an opposite one of the leg portions is compressed, and so that 2) at a second of the locations a) the base portion is bent generally within its plane, b) the one of the leg portions is compressed, and c) the opposite one of the leg portions is stretched. The forward frame module and the rearward frame module are then to opposite ends of the central frame module.