The invention relates to a vehicle air supply system adaptable to occasionally supply large volumes of air at relatively low pressure for purposes such as tire inflation. The system has a compressor, an air dryer, a reservoir adapted to receive air from the compressor via the air dryer, and a controller operable to cause a standard regeneration of the air dryer when a predetermined system condition is met. The controller is also operable to cause an intermediate regeneration of the air dryer in advance of the predetermined system condition being met. The controller is further operable to inhibit the intermediate regeneration. The controller is operable so as to prevent saturation of an air dryer desiccant in circumstances where the compressor is on load for an extended period of time and likely to be pumping a large volume.