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Do shock springs become softer over time? I might buy a used one on ebay from an older model bike and I wanted to see if the rate changed through wear and tear.

I'm not sure if it's the same for bikes, but cars springs lose tensity over time. If i had to guess, i would say yes for bikes too.

All springs do...some worse than others. It's not so much how old it is, but how many times it's been cycled....ie if it was on a garage queen it'll be like new.

OK thanks I thought so.

Johnny Newton's law of increasing mass states: "The relationship of the ratio of sprung mass to the spring rate increases proportionally over time and also increases at an exponintial rate compared to the quantities of beers drank and donuts consumed."

Besides beer and doughnuts, there is the quality of beer can used to make the spring in the first place.

I think I'd be less concerned about the rate than I would the capacity.

A reduction in either is going to show up in a more easily measured spec. If you get a spring for your 'H' KDX that is 460mm long...the proper use of THAT spring does not include cutting a longer preload spacer. THAT spring is junk.

Fork springs develop stress risers (microscopic cracks) over time that will eventually lead to complete failure if the springs are used long enough. Sagging, as I recall, is primarily due to the reallignment of the spring steel molecules over time due to working stresses - the same mechanism forms the surface stress risers which can eventually develop into large cracks in fork springs (that's why shot peening helps extend life). Buying used fork springs is a gamble in that respect - that polished wear found on the outer edges isn't a good thing, even if the rate seems OK. I know this for a fact, as I have had high-time fork springs break while riding.

kawagumby wrote: . . . I know this for a fact, as I have had high-time fork springs break while riding.

Yikes!

How long is "high-time"? Most man-made things in creation get weak and fail eventually, Mom Nature's way of getting revenge for us humans bending molecules in unnatural ways. But I'd expect that most modern day springs would hold up for a good long time under moderate use - 15-20 years before they show signs of "weakening" perhaps?.

'Course my expectations aren't supported by personal experiences like your own !!

The fork springs failed me at about 3 seasons. But that's back when I rode 3-4 times a week. BTW, both failures were while riding a mighty KDX machine. Noticeable sack before that point, so maybe when the springs begin to sack it would be a good time to replace them (even for cheap-skates like me).

I've had brand new Eibachs fail after two rides. 'Fail' meaning one of the pair got a whole lot shorter.

It's not necessarily a lot of use, a lot of time..and it happens to brand name stuff, too.

Another good reason to service your forks a couple times a year if you ride much at all...check that sort of thing out.