Abstract: The suspension, as mounted in duplicate to a truck or trailer frame midway between fore and rear axles of a rear axle pair, is located relatively closely adjacent the rear of said frame; and it utilizes but a single air bag or spring unit, horizontally interposed medially between the axles, yet well spaced forwardly and inwardly from their wheel tires, as a springing agency.This unit acts vertically between the frame and a horizontal rocker arm assembly of the suspension that is coupled front-to-rear with a pair of generally similar leaf spring sets. The suspension affords an equal loading of the leading and trailing rear axles by a total of only two such air springs, each coacting with a fully floating beam, this beam being slidably associated between said spring sets.