Understanding Spring Deflection in Compression, Extension, and Torsion Springs

Definition: Spring deflection, also referred to as spring travel, occurs when a compression spring compresses (under pressure), an extension spring extends (under tension), or a torsion spring twists (radially) upon the application or release of a load.

For deflection to occur in compression, extension, or torsion springs, a load must be applied or released. The distance between the length or position under load and the free or pre-loaded position is recognized as the distance of travel. The traveled distance defines what deflection is, whether through compression, tension, or torsion. Spring deflection is intricately linked to your spring’s rate.

Example 1: The spring rate denotes the force required for your spring to deflect a specific distance during travel. To determine the deflection under a particular load, divide the required load by the spring rate. For extension springs, subtract the initial tension from the load first. In instances where only the spring's required loaded state is known, deduct the loaded position or length from the free position.

Calculate Deflection Using Spring Rate:

Deflection = Load ÷ Rate

D = L ÷ k

Deflection = (Load – Initial Tension) ÷ Rate

D = (L – IT) ÷ k

Calculate Deflection Using Loaded Position:

Deflection = Loaded Position – Free Position

D = LP – FP

Example diagrams:

example of extension spring deflection showing one spring in its free state and the other at extended length

example of torsion spring deflection showing one spring in its free position and the other at torqued position

Example 2: The diagrams to the right illustrate how the provided formulas function. Explore further technical articles in our "Tech Info" section. Numerous articles discuss compression, extension, and torsion spring design. The Spring Creator X tool automatically computes spring rate, maximum safe travel, and maximum safe load. As per the rate formula and example below, maximum safe load and travel are each derived from the other.

Calculate Deflection and Load from Each Other:

Deflection = Load ÷ Rate

D = L ÷ k

Load = Deflection * Rate

L = D * k

Calculate Deflection Using Loaded Length

Calculate Deflection Using Loaded Length

example of compression spring deflection showing one spring in its free length and the other at loaded length

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