Air suspension is close to standard at the top of the market, and the reason is not marketing. Replacing a steel spring with a column of compressed air resolves a compromise that steel cannot escape.
A steel spring has one rate and one length
A coil spring compresses in proportion to load, so a car sits lower with passengers aboard and its ride height changes with what it carries.
Its rate is also fixed by its geometry and material. A spring soft enough for comfort permits excessive body movement, and one firm enough for control transmits road texture.
Engineers work around this with damper tuning and bump stops, but the underlying trade cannot be removed, only positioned.
Air changes rate and height independently
An air spring is a rubber bellows containing compressed gas. Adding air raises the car and increases the pressure, which also raises the effective spring rate.
A compressor and valve block allow the system to adjust each corner, so the car can maintain a chosen height regardless of load.
Because gas compresses non-linearly, an air spring naturally becomes firmer as it is compressed, which gives comfort at small movements and support at large ones.
Height control has effects beyond comfort
Lowering the body at speed reduces frontal area and the air flowing underneath, which improves both aerodynamic efficiency and high-speed stability.
Raising it at low speed provides clearance over obstacles, and lowering it at rest makes entry and loading easier, which matters in a segment where the car is often not driven by its owner.
Self-levelling also means the headlamp aim, suspension geometry and damper working position stay correct whether the car is empty or fully laden.
Adaptive damping completes the system
Air springs are almost always paired with dampers whose resistance can be varied electronically, because a variable spring needs a variable damper to match.
Sensors measure body movement, wheel movement and steering and throttle inputs, and the controller adjusts damping many times per second.
Some systems add a forward-looking camera that reads the road surface ahead, allowing the suspension to prepare for an obstacle rather than react to it.
The cost appears later in the car's life
Air springs are rubber components under constant pressure and thermal cycling, and they eventually perish, usually developing slow leaks rather than failing suddenly.
A leaking spring makes the compressor run more often, and a compressor working beyond its duty cycle is the second failure that typically follows.
This is a significant part of why luxury cars carry high running costs once out of warranty, and why conversions to conventional springs exist for older examples.