A mounting bracket assembly capable of operatively engaging an associated jounce tongue of an associated vehicle suspension and supporting a supplemental air spring assembly in spaced relation to an associated sprung or unsprung mass of the associated vehicle. The mounting bracket assembly can include a first bracket supported on the associated jounce tongue and a second bracket supported on the first bracket. A supplemental suspension system can include an air spring assembly and a mounting spring assembly. A supplemental suspension system kit is also included.