The Ultimate Guide to Testing Coil Springs: Methods, Metrics, and Standards
Coil springs may seem simple, but they perform a critical role in countless applications, from agricultural machinery and precision instruments to automotive and aerospace systems. Ensuring that each coil spring delivers consistent force, deflection, and durability requires rigorous testing.
At Lesjöfors, we have over 175 years of experience in spring manufacturing. As a global leader in the industry, our products are known for their reliable performance and dependable quality. To meet demanding performance requirements, we’ve developed robust testing systems that ensure every spring meets the highest standards and the expectations of our customers.
In this guide, we’ll explore how to test coil springs, why testing matters, and how Lesjöfors uses advanced testing systems to guarantee accuracy, reliability, and compliance with international standards.
Why coil spring testing matters
Springs are designed to store and release energy in a precise, predictable way. Even small variations in coil geometry, material hardness, or surface finish can affect performance, reliability and even safety.
Testing coil springs verifies that they meet specified tolerances for load, deflection, stress, and fatigue life before they ever reach the customer.
These tests prevent:
Premature failure caused by overstressing or material fatigue
Production inefficiencies due to inconsistent spring rates or coil dimensions
Non-compliance with industrial spring testing standards such as ISO 10243, DIN 2095, and EN 1390
How are coil springs tested?
Testing coil springs involves applying controlled loads or forces to measure how the spring responds. Modern systems use digital load cells, displacement sensors, and deflection transducers to collect precise data on how a spring behaves under compression, tension, or cyclic stress.
Types of coil spring tests
Compression testing
A coil spring compression test determines how a spring reacts when compressed under load. This method measures stiffness or spring rate, confirming that the force-deflection curve matches design expectations.
Compression testing also identifies permanent deformation and verifies maximum load at solid height, ensuring the coils don’t bind under maximum compression.
Tension testing
Engineers may also conduct a tensile test of coil springs to evaluate tensile strength, elongation, and stress at break. This spring testing method is primarily used for extension springs, measuring how much the component can stretch before losing elasticity or failing. This spring tension test helps engineers verify material performance and end-coil integrity.
Load testing
A spring load test checks whether load-deflection characteristics remain within defined tolerances across multiple cycles. Load testing validates the linearity of the spring rate and ensures uniform behavior between production batches.
Fatigue testing
Spring fatigue testing simulates real-world operating conditions, compressing or extending the spring thousands, sometimes millions, of times. This test predicts cyclic endurance and establishes a spring fatigue rating, which defines lifespan under specific stress levels.
Visual and dimensional inspection
Although more mechanical than aesthetic, visual and dimensional checks confirm that each coil aligns with CAD data and manufacturing drawings. Automated laser scanners measure coil pitch, wire diameter, and free length, while surface inspections detect potential flaws such as cracks or inclusions before mechanical testing begins.
Spring rate (k value)
The spring rate, or stiffness, defines how much load is required to compress or extend a spring by a certain distance. It follows Hooke’s Law, which states that the force needed to extend or compress a spring is directly proportional to its deflection, as long as the material stays within its elastic limit.
This is expressed mathematically as:
k = F/x, where F is the load (newtons) and x is the deflection (millimeters).
Alternatively, to express the relationship between force and deflection: F = kx
What each symbol means
F: Force or load applied to the spring (e.g., N)
x: Deflection or displacement under load (e.g., mm)
k: Spring rate (N/mm), indicating stiffness. A higher k value means a stiffer spring.
When to use specific symbols
Use k = F/x when calculating stiffness, and F = kx when predicting how much load will create a given deflection.
Elastic limit and set
Every spring has an elastic limit, i.e. the maximum point of deflection it can reach while still returning to its original shape. Beyond this limit, the spring experiences a set, meaning it remains partially deformed. Elasticity and deflection testing ensure the spring’s working range remains within safe limits.
Load at solid height
This test determines how the spring performs at maximum compression, known as solid height. Engineers verify that the coils do not bind or buckle and that material stresses stay within the design envelope.
Stress and deformation analysis
Modern engineering goes beyond physical testing. Lesjöfors uses finite element analysis (FEA) and strain gauge instrumentation to study how forces distribute through a spring under load. These coil stress tests reveal hotspots, potential failure points, and opportunities to optimize coil geometry or wire diameter for better fatigue life.
Testing standards and certifications
Spring testing is governed by international frameworks that define methods, parameters, and reporting protocols.
Key standards include:
F: Force or load applied to the spring (e.g., N)
x: Deflection or displacement under load (e.g., mm)
k: Spring rate (N/mm), indicating stiffness. A higher k value means a stiffer spring.
Testing equipment and technology at Lesjöfors
Lesjöfors operates a wide range of advanced coil spring testing equipment designed to verify every aspect of performance. These include servo-driven compression rigs, which apply controlled loads to measure stiffness and deflection, and laser-based deflection measurement systems that capture even the smallest dimensional changes with high precision.
We also use electromechanical and servo-hydraulic fatigue testers to simulate repeated loading cycles, replicating real-world stress conditions and predicting service life. Automated test rigs combine force–displacement control — measuring how force changes as the spring compresses — with temperature compensation to ensure reliable data under varying test conditions.
All results are analyzed using software linked directly to CAD and simulation data, giving engineers full traceability from digital design through to physical testing. Each test station is calibrated to ISO 7500-1 and complies with ASTM A370, EN 13906-1, and DIN 2096 standards, ensuring every coil spring meets strict international quality and performance criteria.
How are coil springs made at Lesjöfors?
At Lesjöfors, every spring begins with precision manufacturing and meticulous attention to material quality. Using advanced CNC coiling machines, our engineers produce springs to exact specifications before applying heat treatment, powder coating, and shot peening to enhance strength and fatigue resistance.
These production processes are seamlessly integrated with our in-house testing systems, allowing real-time verification of performance parameters.
Watch the full process in action — including key testing procedures such as coil stress testing and materials analysis — in our manufacturing video below:
Sustainable testing practices
Lesjöfors continually refines its testing and production processes to reduce environmental impact. Many of our facilities operate energy-efficient test rigs, use recycled hydraulic media, and run closed-loop cooling systems to minimize energy use and waste. Materials from prototype and fatigue testing are repurposed or recycled wherever possible, ensuring testing remains both precise and responsible.
Our ongoing commitment to sustainability is reflected in our ISO 14001 and ISO 9001 certifications, and in our continued focus on sourcing ethical raw materials and developing cleaner, more efficient technologies.
Contact Lesjöfors about custom spring testing
Lesjöfors offers a full range of spring testing and validation services, from laboratory verification and custom load testing to fatigue life development. Our engineers collaborate with clients across automotive, industrial, and medical sectors to design, test, and refine springs that meet exact performance goals.
Contact us to discuss your testing requirements or learn more about our high-precision testing systems.
Coil springs are tested to verify their performance, durability, and compliance with design specifications, ensuring each spring delivers the correct load, deflection, and fatigue life required for its intended application.
Spring tension and compression are measured using servo-driven test rigs, digital load cells, and laser-based deflection systems. These precision instruments record force–displacement data to calculate spring rate and verify mechanical performance.
Spring fatigue testing evaluates how a spring performs under repeated load cycles. It determines the spring’s fatigue life, predicting how long it can operate before signs of wear, deformation, or failure appear.
If a spring fails any test, engineers conduct a root cause analysis to identify material, design, or manufacturing issues. The spring is then re-engineered or reprocessed to meet all required standards before approval.
Yes. Lesjöfors offers custom spring testing for prototypes and development projects, including load, fatigue, and stress testing. Our engineers can tailor procedures to match specific application requirements and industry standards.
