Passive Suspension
A passive suspension uses mechanical spring and damper characteristics that are not commanded by an electronic controller while the vehicle is moving.
What it includes
Passive does not mean that every force is linear or fixed at one value. Springs can be progressive, and dampers can use velocity-sensitive, frequency-selective, position-sensitive, or pressure-relief valves. A manually adjustable damper also remains passive after the driver or technician selects its setting.
The defining boundary is external control. If a controller changes damping, spring pressure, ride height, or actuator force in real time, that function is adaptive or active rather than passive. A drive mode that changes only steering or accelerator response does not change the suspension category.
Passive systems can be light, durable, and predictable, but one mechanical calibration must balance comfort, body control, suspension travel, and tyre-load variation across many conditions. For the complete taxonomy from passive damping to fully active force control, see Active suspension.