A hydraulic suspension system is a type of suspension used in vehicles to provide a smoother ride by using hydraulic fluid to control the movement of the suspension components. Instead of traditional springs, this system uses hydraulic cylinders and fluid to adjust the height and stiffness of the suspension in response to road conditions and driving dynamics.

In a hydraulic suspension, a pump circulates hydraulic fluid through a series of cylinders that are connected to the wheels. These cylinders can extend or contract, allowing for changes in ride height and damping characteristics. The system can automatically adjust the vehicle's ride height based on factors like load, speed, or terrain, providing better handling, comfort, and stability.

Hydraulic suspension systems are commonly found in high-performance, luxury, and off-road vehicles, offering superior ride quality and control compared to traditional suspension systems. Some examples include the Citroën hydropneumatic suspension, and advanced systems like Mercedes-Benz's Airmatic or Audi's adaptive air suspension.