Spring Selection Guide: Force, Stroke, and Mounting Explained
A spring selection guide for gas springs provides the technical parameters and calculation methods needed to choose the correct gas spring for a specific application. Selecting the wrong gas spring leads to premature failure, safety hazards, and costly redesigns. This guide covers force calculation, stroke determination, mounting considerations, and environmental factors critical for industrial and automotive applications.
⚡ In a Rush? Key Takeaways
- Gas spring force = (Weight × Distance to CG) ÷ (Number of springs × Distance to mount)
- Stroke length must match mounting point travel, not lid arc (typically 10-15% extra for preload)
- Mounting angle reduces effective force by cos(angle); 30° angle loses 13% force
- Apply 15-20% safety factor for temperature extremes and cycle life degradation
- ✅ Use verified application data with the gas spring force calculator for accurate selection
How do I calculate the required force for a gas spring application?
Required gas spring force = (Lid weight × Distance from hinge to centre of gravity) ÷ (Number of springs × Distance from hinge to spring mounting point)
The force calculation begins with the lid’s weight and geometry. Measure the lid’s total weight in Newtons or convert pounds to Newtons (1 lbf = 4.448N). Determine the centre of gravity (CG) distance from the hinge axis. For symmetrical lids, CG is at half the width. For irregular shapes, calculate or measure the balance point.
Next, measure the distance from the hinge to where the gas spring mounts on the lid. This creates a lever arm. The formula accounts for how many springs share the load. Always use metric units (Newtons and millimetres) for consistency with gas spring specifications.
- Example: 20 kg lid (196N) with CG 200mm from hinge, two springs mounted 150mm from hinge
- Force = (196 × 200) ÷ (2 × 150) = 39,200 ÷ 300 = 130.7N per spring
- Select next standard size up (150N) for 15% safety margin
- Verify with supplier datasheet for force at mid-stroke
What stroke length do I need for my gas spring installation?
Stroke length = Maximum distance between mounting points minus minimum distance, plus 10-15% for compression preload.
Stroke is not the lid’s travel angle but the actual linear distance the gas spring compresses and extends. Model the hinge and mounting points in CAD across the full lid motion (closed to open). Record the distance between spring mounting points at each position. The difference between maximum and minimum distance is the required stroke.
Add 10-15% to this measurement for compression preload. This ensures the spring remains slightly compressed when the lid is closed, preventing buckling and ensuring immediate force application. Ignoring preload leads to slack in the system and poor hold-open performance.
- Measure distance between mounting points with lid fully closed (Position A)
- Measure distance with lid fully open (Position B)
- Stroke = |Position B – Position A|
- Add 10-15%: Final stroke = Stroke × 1.15
- Example: 100mm measured travel → 115mm selected stroke
How does mounting angle affect gas spring force?
Effective force = Rated force × cos(θ), where θ is the angle from vertical; 30° angle reduces force by 13%.
Gas springs are designed to operate most efficiently with the rod end pointing downward (vertical). When mounted at an angle, only the vertical component of the force contributes to lifting the lid. The cosine of the angle from vertical gives the force multiplier. At 30° from vertical, cos(30°) = 0.866, meaning 86.6% of rated force is effective.
For horizontal mounting (θ=90°), cos(90°)=0, providing no lifting force—use only for damping or counterbalance applications. Always specify mounting angle in your calculation. If the angle changes during operation (e.g., a lid that starts vertical and ends horizontal), calculate the force at the most critical point, usually where the lid needs maximum hold-open force.
| Mounting Angle from Vertical | Cosine Value | Effective Force (% of Rated) |
|---|---|---|
| 0° (Vertical) | 1.000 | 100% |
| 15° | 0.966 | 96.6% |
| 30° | 0.866 | 86.6% |
| 45° | 0.707 | 70.7% |
| 60° | 0.500 | 50.0% |
What end fittings should I choose for my gas spring application?
Choose ball sockets for quick installation, clevis for high-vibration environments, and eyelets for bolted mounting—match to your mating hardware.
End fittings determine how the gas spring attaches to the application. Ball sockets (10mm or 8mm diameter) snap onto ball studs, offering fast installation but limited misalignment tolerance. Clevis brackets use a pin and provide better vibration resistance and angular flexibility. Eyelets require a through-bolt and suit applications where welding or stud mounting isn’t feasible.
Match the fitting diameter to your stud or bolt size. For carbon steel applications in dry environments, zinc-plated fittings suffice. For marine, food processing, or outdoor exposure, specify 316 stainless steel fittings. Never mix metric and imperial fittings—10mm ball sockets require 10mm studs, not 3/8″ (which is 9.5mm).
- Ball socket: Best for enclosure lids, cabinet doors, and light-duty hatches
- Clevis: Preferred for industrial machinery guards, vehicle compartments, and high-cycle applications
- Eyelet: Used when bolting directly to a bracket or frame is necessary
- Threaded stud: Allows minor force adjustment via preload nut (limited to ±10%)
How do I account for temperature effects in gas spring selection?
Gas spring force decreases approximately 1.5% per °C below rated temperature; apply low-temperature rating for <0°C applications.
Standard gas springs are rated for force at 20°C (68°F). Below this temperature, nitrogen pressure drops, reducing force.
