A system is provided for use on large vehicles of the type wherein the vehicle frame (12) is supported on vehicle axle assemblies (14, 20, 22) through air bags (26, 30, 32), and each air bag has a lower end coupled to the lower end of an arm such as a swing arm (112) whose upper end is pivotally mounted on the frame. The height of the air bag is sensed by a pair of tilt sensors (50, 52), one on a tilt arm such as the swing arm (112), that has one end pivotally connected to the vehicle frame and an opposite end at least pivotally connected to the vehicle axle assembly. The other sensor senses tilt of the vehicle frame about an axis parallel to the axes of pivoting of the tilt arm. Each tilt sensor senses tilt of its location with respect to gravity, and the difference in tilt indicates air bag height.