A power train configuration for an amphibious vehicle especially well suited for sit-astride applications. A prime mover drives a marine propulsion unit and/or at least one road wheel wherein the such road wheel is driven through a speed-change transmission. The speed-transmission is positioned above or below the axis of the prime mover's output shaft and preferably such that its input and output shafts are aligned at an angle of up to 90 degrees relative to the vehicle's longitudinal and lateral axes and/or the axis of the prime mover's output shaft.