The calculation of maximum load, or the highest force a spring can withstand before deformation or failure, is a fundamental aspect of spring design. Two crucial parameters come into play here: maximum shear stress and maximum deflection or solid height. The focus on shear stress becomes higher for equipment that encounters irregular forces, as it has a direct effect on the structural integrity of the spring. Conversely, maximum deflection is of greater importance in applications like machine mechanics or toys where the load application is relatively constant. Comprehending these parameters in their respective contexts is crucial for successful spring design.

Maximum Shear Stress

The maximum load a spring can handle can be determined through the evaluation of Maximum Shear Stress. This concept encapsulates the internal resistance a spring possesses against deformation from an external force. The unit of measurement is Pascals (Pa) and is calculated with this equation: Shear Stress = Force / Area. 'Force' indicates the external influence on the spring, while 'Area' pertains to the cross-sectional area of the spring wire.

Both the magnitude of the external force and the area of the spring wire across which the force is dispersed factor into the calculation of maximum shear stress. Amplifying the force or reducing the spring wire's area leads to an increase in shear stress, potentially causing deformation or failure of the spring. The logic behind this can be illustrated through the case of a spring used in a high-stress application such as a car suspension system. Here, a thicker wire is chosen for its greater cross-sectional area, which is better able to disperse the impact, and as a consequence, minimizes the shear stress.

Spring design involves accommodating the expected external forces and ensuring an adequate spring wire cross-section to distribute this force without inducing deformation. However, these parameters are not independent and interact with one another. Increasing the spring wire area can counteract high-force effects, but may also lead to a decrease in the spring's flexibility and overall functionality. Hence, achieving the right balance is important. This is often based on the Spring Index, a parameter that correlates the spring's resistance to its diameter and wire size, without involving the actual dimensions.

Maximum Deflection (Solid Height)

The maximum deflection, additionally referred to as solid height, is used to determine a spring's maximum load. It signifies the extent to which a spring can compress before permanent deformation occurs. The deflection is calculable using the equation: Deflection = Load / Spring Rate. In this equation, 'Load' signifies the external force exerted on the spring, while 'Spring Rate' is indicative of the spring's ability to react to this force. The spring rate is a measure of the change in load per unit change in length.

The maximum deflection of the spring is decided by the applied load and the spring rate. A larger load or a lower spring rate results in a greater deflection, pushing the spring towards its maximum load-bearing limit. For example, a spring with a spring rate of 5 N/mm under a 100 N load will experience a deflection of 20 mm. If the spring rate is reduced to 4 N/mm, the same 100 N load causes a deflection of 25 mm. This illustrates the inverse relationship between spring rate and deflection.

These calculations assist engineers in ensuring that anticipated deflection under a specific load does not surpass the maximum deflection allowed by the spring design. Adjusting the spring rate and load values helps in the construction of springs that maintain functionality without the risk of deformation from overload or surpassing the maximum deflection.


Understanding how to calculate the maximum spring load is a necessary aspect of spring design for engineers. It involves factoring in elements such as shear stress and deflection which can influence the load a spring can support.

During the design process of springs, it's necessary to include a safety margin. This allows for changes in material properties, differences in manufacturing methods, and variations in load conditions that can occur in practice. This way, you can prevent springs from exceeding their load limit and experiencing failure.