The air in the bags significantly reduces the noise and vibration transmitted from road surfaces. Newer torsion bars are encased in hard rubber inside the sleeve to further buffer the road noise and vibration between the axle and the chassis. Eagle passenger buses made this suspension famous and many entertainers will only use Eagle buses for touring because of their ride characteristics. Foretravel and Safari are the major motorhome builders that use or have used this suspension system. Ride-height is adjusted by loosening the lever arm and twisting the bar with special tools and then tightening the arm.
Adjustment is limited and when the bar ages, replacement is relatively expensive.
Torsion bar suspensions are used on some travel providing lower ride levels and thus a lower center of gravity. Torsion bars are used in some automobiles and light duty trucks. I have driven buses and motorhomes with all types of suspensions and personally favor the eight air bag system for its excellent side to side stability, lower noise and vibration coupling, comfort and automatic ride height adjustment. The independent front four air bag system is also very good. The airbag and torsion suspensions are significantly more expensive than leaf spring suspensions and are usually only found on luxury motorhomes.