The air suspension system is mounted onto the chassis with fixed suspension support. On the other side of the axle, we find the air suspension bellows. When these bellows receive air pressure, the trailer moves up.
Usually a trailer suspension consists of more than one axle.
These axles are all connected, so they carry the same amount of weight. The weight is evenly distributed.
The air suspension system acts as the first loading point, which is the theoretical centre of the tridem or the average location between the axles. The second loading point is the kingpin or the coupling between the truck and the trailer. Unlike the kingpin, the air suspension is flexible. Lifting the last axle shifts the load point towards the front, which helps distribute the weight in the trailer.
Lifting the first axle shifts the loading point to the rear, which redistributes some of the weight towards the front. This saves the tyres and brake pads when the trailer is empty and gives more traction when it is loaded.