# Calculating pretension of a spring with an initial tension

Simple one. Some extension springs are wound with an initial tension which acts to pull the coils together, even when not under external loading.

When calculating the preload in the spring, should the initial tension be added to the spring force (e.g. initial length x spring rate)? I have seen a few examples and some people include it, others don't. Which is correct?

• So, to paraphrase: "When I put force A into a spring, and then add force B, is the total force in the spring B or A+B?". Apr 9 '18 at 9:06