Abstract: An improved foil thrust bearing having a thrust runner and a thrust plate includes an underspring element positioned adjacent to the thrust plate. The underspring element comprises, in one embodiment, a plurality of alternating first apertures and spring portions, with at least one spring portion having a periodic configuration and comprising a leading edge and a trailing edge. The periodic configuration is defined by a plurality of pitches that vary between the leading and trailing edges. Also defining the periodic configuration is a plurality of periodic elements that vary in longitudinal length between the leading and trailing edges. A thrust bearing disk is disposed intermediate the underspring element and the thrust runner. The disk comprises a plurality of transition areas that provide a stepped configuration to the disk. The transition areas match a plurality of circumferential positions of the first apertures in the underspring.