Going through the mechanics of calculating extension spring stroke is a requisite for those engaged in designing utility items ranging from car safety features to fitness equipment. This article delves into how to ascertain extension spring stroke based on force, with the objective of aiding you in creating better designs.

Consider the case of a car's seat belt where, an incorrect estimate of spring stroke could lead to a loose belt, compromising safety. Hence, it's critical to grasp the art of accurately determining stroke length.

We'll explore how in some instances, the spring constant, which depends on the spring's dimensions, experiences deviations. Most often in systems where tension remains consistent, such deviations are infrequent. It all ties back to the dependable Hooke's Law, to which extension springs adhere up until they reach their elasticity limit. Exceed this limit and chances of deformation or breakage rise. By the conclusion of this article, you should have a thorough understanding of these factors and be prepared to confidently design and choose your extension springs.

Calculating Stroke from Force

The extension of an extension spring, described as its stroke, increases when an external force is applied. In-order to compute this, one needs the applied force. Let's use a basic extension spring to elucidate: Assume a force increase of 50N results in a 20cm spring extension. This equates to a 0.4cm extension for every 1N increase in force (20cm/50N = 0.4cm/N). This particular calculation is based on a linear force-displacement relationship. Whereas, extension springs with non-linear force-displacement relationships necessitate a different computation.

We could examine this in the domain of automobile suspension systems. Here, spring stroke is calculated with precision. Extension springs perform functions such as shock absorption and maintaining stability. A calculation that overestimates the stroke length could lead to a spring extending beyond its limits, resulting in damage. Conversely, an underestimated stroke length might result in a ride that could be perceived as rough due to suboptimal shock absorption. Consequently, recognizing the force-stroke relationship is a relevant step in design.

We should highlight that the force-stroke relationship isn't the same for all extension springs. Springs with an inconsistent cross-sectional area or a varying pitch may not exhibit a linear relationship. In these instances, engineers commonly use methods such as advanced mathematical modeling or simulation tools to anticipate a spring's behavior with precision.

When Nonlinearities Arise

The stroke of an extension spring is impacted by any deviations within the force-displacement curve. These deviations, or nonlinearities, emerge when the spring deforms over its elastic limit, leading to challenges in the calculation process using traditional techniques.

In situations with considerable nonlinearity, comprehensive mathematical models or numerical methods may be necessary. The finite element method is one such solution that accounts for alterations in coil diameter, deformation, and displacement. Generally it is not recommended to operate springs beyond their elastic limits except in emergency situations.


For proper design and choice of extension springs, understanding of extension spring stroke calculation is necessary. It's important to have knowledge about factors like force, its effect on stroke, the correct calculation of the spring constant, and handling nonlinearities. Accurate stroke calculation might require some test runs or simulations that consider the unique properties of the spring and its usage circumstances. Careful application of these considerations will ensure the right calculation results and help improve designs in applications where extension springs are used.