The figure also provides an additional overview of the contrast between steel springs and air springs.
It is evident that level-control function of air-springs allow for the omission of the static spring deflection, which means that the entire spring travel is available for dynamic wheel motion. Hence suspensions can be designed along a softer characteristic to improve comfort (especially significant to heavy trucks and busses).
Unlike the steel spring, the air spring also shows a progressive rise of the spring stiffness with spring travel.

This brings us to the end of the first lecture dealing with the suspension systems of vehicles. The next lecture takes a look and damper systems.