An air spring has a piston formed of a high strength plastic material consisting of a main shell and a bottom end sealing plate extending between a pair of concentric inner and outer annular walls. A pair of internal auxiliary reservoirs or subchambers are formed within the piston and are in fluid communication with each other and with the main air chamber formed by a flexible bellows extending between the piston and an end plate. A plurality of radially extending reinforcing ribs extend between the inner and outer annular walls of the shell and a rigid central post. A central planar support surface having an area approximately 20% than that of the piston base area provides a reduced surface area for mounting the piston on a smaller support surface.