Damper and Awe: 6 Types of Automotive Dampers Explained

May 08, 2023

Dampers are largely responsible for determining a car's driving character, so choosing the right one matters.

From the June 2017 issue

First, they’re called dampers, not shocks. And dampers, as any suspension engineer will tell you, get no respect. In fact, considered against the noisier, flashier, and more easily seen components of the automobile, these inconspicuous components may be the most underappreciated pieces on a car. Their job—keeping the tires on the ground to accelerate, brake, and turn, while making the ride livable—is rather important. And though damper calibration is one of the last elements to be finalized in suspension tuning, it's the part that endows a chassis with its personality. Here's a breakdown of the most popular varieties:

Found in: Audi A4, Mazda MX-5 Miata

This design uses a single cylinder split by a floating divider into oil and gas chambers. A shaft pushes the piston in the cylinder to create damping force. During compression, oil is metered through a shim stack on the shaft side of the piston. In rebound, shim stacks on the face of the piston control flow. Gas (often nitrogen) in the chamber is squeezed during compression to compensate for the oil displaced by the shaft. Damping force is determined by the shape, size, and number of shims on the piston, the shaft diameter, the cylinder diameter, and gas pressure.

Found in: Cadillac CT6, Chevrolet Impala, Ram 1500

As its name implies, a twin-tube damper uses two concentric tubes. The inner tube is filled with oil and houses the shaft and piston. Like a monotube damper, shim stacks on the piston meter oil flow in both compression and rebound, creating damping force. An additional shim-stack valve, called the base valve, directs oil flow into the outer tube (reservoir) during compression, contributing to the damping rate. During rebound, oil returns from the reservoir to the main chamber via a check valve. The outer tube is partially filled with compressible gas, which compensates for the shaft volume during compression and forces oil from the outer tube into the inner tube during rebound. Damping force is determined by the same factors as a monotube damper with an additional contribution from the base valve. Tuning twin-tube dampers is accomplished by adding or removing shims.

Found in: Ford F-150 Raptor

The Fox twin-tube dampers found on Ford's flying pickup couple long travel with position-sensitive damping. Multiple circuits are involved in creating damping force in the middle 50 percent of travel.In that zone, most fluid bypasses the piston through holes in the inner tube, refilling behind the piston as it moves through refill holes. Some oil also passes through shim-stack valves in the piston and, in compression, through the base valve. The size, position, and shimming of the bypass holes progressively increase the damping rate the more the suspension compresses or rebounds. When the piston passes the last bypass hole, fluid primarily routes through the shim stack on the piston, substantially increasing damping force. A base valve plays a role during the full length of the compression stroke and regulates fluid flow to the external reservoir to provide consistent compression damping and to mitigate cavitation (air pockets forming in the oil) during high-velocity events.

Found in: Cadillac CTS-V, Chevrolet Corvette, Ferrari 488GTB, Lamborghini Huracán

With no valves to dictate damping rates, MR units control wheel and body motions by effectively changing the viscosity of the oil. Though their construction is relatively traditional (a piston at the end of a shaft moving inside a tube of hydraulic fluid), their operation is anything but. Current-generation MR dampers use two electromagnetic coils located in the piston to generate a localized magnetic field around the piston's passages. The hydraulic fluid inside the dampers contains tiny iron particles, distributed randomly before electric current is applied to the piston coils. Applying current to the coils creates a magnetic field, which arranges the particles into lines, making the fluid more resistant to flow. When pressure on either side of the piston is sufficient to break apart the lines of particles, fluid flows through the passages, allowing the piston to move. The strength of the particles’ alignment is proportional to the force of the magnetic field so that changing the amperage to the coils changes the damping force.

Found in: Chevrolet Camaro ZL1 1LE, Chevrolet Colorado ZR2

The seemingly simple spool-valve damper takes the trial and error out of passive damper tuning by permitting engineers to achieve the exact force/velocity curve they choose using known hydraulic equations. Spool valves, which consist of a spring-loaded disc acting as the lid of a topless cylinder, allow oil to flow through precisely shaped ports in the sides of the cylinder as the spring is compressed. The area of the port exposed to permit oil flow is a function of the force applied to the disc. The greater the force, the more area is exposed for oil to flow through. The shape, size, and location of the ports and the stiffness of the spring determine damping force. Spool-valve dampers vary in the placement of their valves, though the simplest varieties used on road cars locate a spool valve on both sides of the piston—one to manage compression and one for rebound.

Found in: Ford Focus RS, Infiniti Q50 and Q60, Volvo S90

In most adaptive-damper designs, a combination of electronically controlled valves and passive shim-stack valves dictate damping force. Available in both monotube and twin-tube configurations, placement of their electromechanical valves may vary. This twin-tube example, a new model designed by supplier Tenneco, uses a check valve on the backside of the piston, which permits the piston to move through the compression stroke with very little resistance. During compression, pressure builds in the inner tube as the shaft displaces oil, causing it to flow through the base valve at the bottom of the damper and through the electronically controlled valves at the top of the damper. Compressible gas is used in the reservoir to compensate for the oil displaced by the shaft during compression. Flow is metered during rebound by the shim stack on the face of the piston and through the electronically controlled valves at the top of the piston. Oil returns to the inner tube during rebound via a check valve located underneath the base valve. Opening or closing the valves at the top of the damper varies damping force in both compression and rebound.

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