How ECAS works
The axles are mounted on the chassis with a hinged suspension bracket. On the other side of the axle, we find the air bellows. When these air bellows receive air pressure, the trailer is pushed upwards.
Normally a semi-trailer suspension consists of more than one axle. The air bellows of these axles are all connected to each other so that they carry the same weight. Does it look like your semi-trailer is tilting backwards? Don't worry, the weight is still evenly distributed over all three axles. Because these three axles distribute the weight evenly among themselves, the theoretical loadbearing point is at the centre of the middle axle. This point is the tridem or average position between the axles.
Our second loading bearing point is the kingpin or the coupling between the tractor and the semi-trailer. Unlike the kingpin, the air suspension is flexible. By lifting the last axle, you shift the theoretical load point forward, which helps distribute the weight in the trailer evenly. Useful options here are the Optiturn and Opti-load.
By lifting the first axle, the loading point shifts backwards, and more weight is placed on the kingpin. This saves on tyres and brake pads and gives the tractor’s pulling axle more traction when it’s loaded. This is linked to traction help, a handy ECAS option.