Extension Spring Loop Stiffness Contribution

[BiPolarMoment]

I think this is a dumb question but I may be the dumb one so I figured I would ask it here and get a more authoritative answer:

Does the loop end condition in an extension spring contribute at all to the spring load expected when deflected? i.e. would it definitively indicate a different initial tension and/or spring rate?

Exaggerated mockup for example:

Actual picture:

If it's not obviously implied, there are some that are placing some importance in this gap (or more accurately, how much of the spring is part of the end-loop) where I do not anticipate any from a functional standpoint (when new). My concern is their focus will lead to erroneously associating this loop condition with the ability of the spring to perform its function getting mixed in as a potential cause for alarm. I believe part of the reason this association exists is that we had a supplier in the past supplying springs with visibly varying loop end conditions with different spring properties (we measured)--however, I discovered that those springs also had slightly different wire diameters, free-lengths and coil counts which fully explains the property discrepancies in that instance without focusing on the free-end condition (i.e. they were not the same spring at all). That is no longer our supplier; the springs presently in question are now sourced directly from the manufacturer of origin, not a reseller.

Am I the dumb one?

Somewhat related follow up questions:
- Is it not reasonable to expect variations in this 'gap' (as supplied) between the free-end loop and the barrel of the spring if it is not stated by the manufacturer as being a controlled dimension?
- Is it unexpected that this gap will change over the life of a spring if used within it's design parameters (i.e. not exceeding maximum extension)?

If maximum extension is exceeded, will the free-end be the expected visually noticeable point of yield (or would it occur within the coil first)?​

 

[3DDave]

That part of the spring typically has no load on it. It's just a loose end that retains the spring when there's no load on the remainder of the spring.

 

[BiPolarMoment]

Yes... that was my point, lol.

 

[3DDave]

Your question:

"Does the loop end condition in an extension spring contribute at all to the spring load expected when deflected?"

LOL, was that your point?

"Is it not reasonable to expect variations in this 'gap' (as supplied) between the free-end loop and the barrel of the spring if it is not stated by the manufacturer as being a controlled dimension?"

Yes, it is not reasonable to have any expectation for that gap if the manufacturer doesn't control it.

"Is it unexpected that this gap will change over the life of a spring if used within it's design parameters (i.e. not exceeding maximum extension)?"

Already answered.

"If maximum extension is exceeded, will the free-end be the expected visually noticeable point of yield (or would it occur within the coil first)?"

That depends on how much the maximum extension is exceeded and how much preload is wound into the spring. I would expect the remainder of the spring to be badly damaged before the loop changed.

 

[BiPolarMoment]

I believe we are on the same page. Like I said, dumb question--I need to have backup to contend with what I guess I would compare to a superstition.