Abstract: Provided is a unitized auxiliary lift axle suspension system for wheeled vehicles having frame-to-ground clearance of about 37 inches or more. The suspension system weighs less than about 550 lbs. and usually less than 500 lbs., is certifiable at greater than about 18,000 lbs./axle and is adaptable to a wide variety of vehicle frame widths. The system generally comprises a pair of upwardly biased leaf springs and, for each leaf spring, a spring retaining means for retaining the spring at about its central portion, and air bags located on either end of the spring retaining means, the spring retaining means being sufficiently long to provide a platform for said air bags, but insufficiently long so as to allow the leaf spring to flex below its flat spring condition. The system further comprises spring hanger means having at least one vertical wall for retaining the leaf springs at their ends.