A modular track suspension system is readily adapted for attachment to any presently manufactured full-size automotive vehicle (10) built with a load-carrying frame (12), being easily substituted for the vehicle's conventional wheeled undercarriage either during or following final assembly. The module uses a pair of endless rubber tracks (14, 15), one track under each respective side of the vehicle; and each track (14, 15) is supported over tandem units (17, 18) with, preferably, side-by-side dual-wheels (20, 21 and 22, 23) having rubber tires. The dual-wheels are each movable in a vertical plane, and each dual-wheel can move separately and independently of the similar independent movement of the other dual-wheel with which it is in tandem. Each dual-wheel is also resiliently biased in the direction of the terrain on which the vehicle is standing or moving.