Gas Shock vs Gas Strut: Key Differences Explained

What Is a Gas Shock?

A gas shock, also known as a damper or shock absorber, is a hydraulic device designed to absorb and dissipate energy from suspension movement. The primary function of a gas shock is to control oscillation—the bouncing and compression cycles that occur when a vehicle’s suspension compresses and extends over uneven road surfaces.

Gas shocks are pressurised internally with nitrogen gas, typically at pressures between 50–200 bar (725–2,900 psi), depending on the vehicle and shock specification. This gas charge prevents cavitation (the formation of vacuum pockets) inside the shock during rapid compression and decompression cycles, which would otherwise cause the internal piston to lose contact with the hydraulic fluid and reduce damping effectiveness.

The internal structure of a gas shock contains:

• A piston rod attached to the vehicle’s suspension component (strut tower or control arm)
• A piston head with calibrated orifices that restrict hydraulic fluid flow
• A sealed cylinder filled with hydraulic oil
• A pressurised gas chamber (usually nitrogen) separated by a floating piston or bladder
• Mounting points (typically a rod eye at top, mounting point at base)

Gas shocks are mounted vertically in the vehicle’s suspension and move through a defined stroke length—typically 100–200 mm—during normal driving. They cycle thousands of times per journey, absorbing the energy of suspension movement and converting it to heat that dissipates through the shock housing.

What Is a Gas Strut?

A gas strut, also called a gas spring or strut damper, is a pressurised chamber designed to support weight and hold a component in a fixed position against gravity. Unlike shocks, gas struts do not absorb rapid cyclical movement; instead, they provide a constant upward force to counteract the weight of a lid, panel, or hatch.

Gas struts are pressurised to much higher forces than shocks—typically between 200–4,000 N (Newtons) depending on the application. A gas strut rated at 1,000 N, for example, exerts 1,000 N of upward force when fully extended, which is equivalent to supporting approximately 100 kg of weight.

The internal structure of a gas strut is simpler than a shock:

• A piston rod sealed inside a cylinder
• A pressurised nitrogen chamber on one side of the piston
• A small volume of hydraulic fluid for damping (minimal, compared to shocks)
• A sealed cap at one end
• End fittings: typically ball sockets, clevis mounts, or eye mounts on both ends

Gas struts are fixed at both ends: one end attaches to the component being supported (lid, door, hatch), and the other end anchors to the chassis or frame. When you push the lid down, you compress the gas inside the strut. When you release it, the pressurised gas pushes back, lifting the lid open and holding it at a height determined by the gas force rating.

Core Functional Differences

Primary Purpose and Force Type

The fundamental difference between gas shocks and gas struts lies in their intended function. A gas shock is a damping device—it absorbs kinetic energy from cyclical movement and dissipates it as heat. A gas strut is a support device—it generates a constant upward force to counteract gravity.

Gas shocks work passively: they respond to suspension movement by restricting hydraulic fluid flow through calibrated orifices, which slows the movement and reduces oscillation. Gas struts work actively: they continuously push upward with a fixed force rating, regardless of how much the strut is compressed or extended within its stroke range.

Stroke and Cycle Behaviour

Gas shocks are designed for repeated, rapid compression and extension cycles. A typical shock on a passenger car may cycle 1,000–3,000 times per hour during highway driving. This continuous movement generates friction and heat, which is why shock absorbers can become hot to the touch during or after a long drive.

Gas struts, by contrast, are designed for infrequent, slow movement. A car boot lid that opens and closes 10 times per day will cycle a gas strut only 10 times daily. Over a year, that’s approximately 3,650 cycles. A gas strut rated for 50,000 cycles can therefore last 13+ years in typical domestic use. Because gas struts move slowly and infrequently, they generate far less heat and wear much more slowly than shocks.

Force Output Characteristics

Gas shocks generate damping force that is velocity-dependent: the faster the suspension compresses or extends, the greater the damping force. This is why a shock feels firm when you bounce the vehicle quickly but soft when you press down slowly. The valving and orifice design are calibrated to provide appropriate damping across a range of speeds.

Gas struts generate force that is position-dependent but relatively constant. A 1,000 N strut exerts approximately 1,000 N whether the lid is 10 mm or 100 mm open (within its design range). This consistent force is what allows the strut to hold a lid in any open position—the gas pressure remains roughly stable throughout the stroke.

Pressure and Gas Charge Differences

Gas shocks and gas struts use different internal pressures and gas charge strategies.

Gas shocks typically use nitrogen precharge pressures between 50–200 bar. The exact pressure depends on the shock design and the vehicle it’s intended for. A typical sedan shock might have a 100 bar nitrogen charge. The relatively lower pressure in a shock allows for smoother damping characteristics and is easier to control with calibrated orifices.

Gas struts use much higher pressures because they need to generate significant force in a compact space. A 1,000 N strut might have an internal nitrogen pressure of 150–200 bar, but this pressure acts on a small piston area. The high pressure-to-area ratio produces the high force output. Some industrial-grade struts operate at pressures exceeding 250 bar.

The gas charge in shocks serves primarily to prevent cavitation and maintain damping consistency. The gas charge in struts is the primary load-bearing mechanism—it is the reason the strut holds anything up at all.

Application and Mounting Differences

Where Shocks Are Used

Gas shocks are found in vehicle suspension systems, typically mounted vertically between the vehicle chassis and the suspension control arm or strut tower. Common applications include:

• Passenger car suspension (vertical shock mounts)
• Truck and SUV suspension (often twin-tube or monotube designs)
• Motorcycle suspension (rear shock absorbers)
• Off-road vehicles (often remote-mounted with external linkage)
• Heavy machinery and agricultural equipment suspension

Shocks must be mounted to allow free piston rod movement throughout their design stroke. Mounting is typically rigid: a top mount on the strut tower or frame and a bottom mount on the control arm or axle housing.

Where Gas Struts Are Used

Gas struts are found in applications requiring weight support and controlled opening, typically mounted horizontally or at an angle. Common applications include:

• Car boot (trunk) lids and bonnet (hood) hoods
• Hatchback and tailgate doors
• Caravan and motorhome locker doors and cupboards
• Furniture: ottoman storage beds, kitchen overhead cabinets, loft hatches
• Marine: boat engine hatches, companionway doors, storage lockers
• Industrial: machine guards, cleanroom panels, server cabinet doors
• Sunroofs and panoramic roof panels

Gas struts are designed for non-vertical mounting and can be installed at almost any angle. The force output changes slightly with angle (it’s maximum when fully horizontal), but modern struts work effectively even in tilted or nearly vertical positions.

Replacement and Maintenance Differences

Shock Replacement

When a vehicle shock fails, symptoms typically include excessive bouncing, poor handling, uneven tire wear, or a feeling of instability on corners. Shocks are often replaced as a pair or set to maintain balanced suspension performance. Replacing a single shock leaves the opposite side with older damping characteristics, creating asymmetrical handling.

Shock replacement requires disconnecting the piston rod from the strut tower and the mounting point from the control arm, then withdrawing the shock vertically. Installation is the reverse process. Most shocks are not user-serviceable—they cannot be rebuilt or refilled and must be replaced as complete assemblies.

Gas Strut Replacement

When a gas strut fails, symptoms include a lid or hatch that no longer opens with light pressure, slowly falls closed when held up, or won’t stay open when propped. Unlike shocks, gas struts can often be replaced individually because each application typically has only one or two struts supporting that component.

Gas strut replacement is often a straightforward DIY task: disconnect the ball socket or clevis ends by removing the pins or clips, slide the old strut out, and slide the new one in. No special tools are usually required. Struts can occasionally be recharged by a specialist if the core is sound, but single-unit replacement is standard practice.

Force Rating and Specification

The most obvious difference when specifying these components is how they are rated.

Gas shocks are typically specified by vehicle make, model, year, and suspension position (front or rear). They may also be specified by shock type (monotube, twin-tube, remote reservoir) and intended use (street, sport, off-road). Force output is not usually listed on a shock absorber—damping rate is instead expressed through the shock’s internal valving and orifice design.

Gas struts are specified primarily by force rating in Newtons (N). A strut rated at 500 N lifts approximately 50 kg; a 1,500 N strut lifts approximately 150 kg. Additional specifications include extended length (fully open), compressed length (fully closed), stroke (the difference between open and closed), and end fitting type (ball socket, clevis, stud, eye mount).

For automotive applications, gas struts are also specified by vehicle make and model. Measuring an existing strut is the most reliable way to ensure you order the correct replacement.

Cost and Durability

Gas shocks are typically more expensive than gas struts for equivalent vehicles, often ranging from £80–£400 per shock depending on vehicle and quality. Industrial or high-performance shocks can exceed £500 each. Shocks have a finite lifespan—typically 50,000–150,000 km depending on road conditions and driving style—and are a wear item that most vehicle owners will replace at least once.

Gas struts are generally less expensive, ranging from £15–£150 depending on force rating and application. Automotive boot struts are typically £30–£80 per pair. Furniture and general-purpose struts are often £20–£60. Because struts cycle infrequently, they last significantly longer: 10–20 years in domestic use is common. Industrial-grade struts designed for frequent cycling can be rated for 100,000+ cycles.

Summary: Key Takeaways

The difference between a gas shock and a gas strut can be summarised in this single sentence: shocks absorb cyclical movement; struts support static weight and hold components open.

Gas shocks are velocity-sensitive damping devices mounted vertically in vehicle suspension to control oscillation and provide smooth ride quality. They cycle thousands of times per journey, generate heat, and are rarely user-replaceable. Force output depends on the speed of suspension movement, not a fixed rating.

Gas struts are position-dependent support devices mounted at angles to hold lids, doors, hatches, and furniture open against gravity. They cycle infrequently, generate minimal heat, are often user-replaceable, and are specified by fixed force ratings in Newtons. They generate constant upward force regardless of how much they are compressed or extended within their design range.

Confusing these two components can lead to incorrect ordering and failed replacement attempts. If you are unsure whether you need a shock or a strut, consider: Does the component move constantly during normal use (shock) or does it open and close infrequently and need to stay open (strut)? This distinction will guide you toward the correct component and help you calculate the correct force rating if needed.