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Do Fork/Shock springs ever wear out??

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#1
What’s all this talk about springs wearing out? Don’t most spring steels have an infinite endurance limit? With that said if the internal stresses of the spring are below the yield (and they should be) strength of the material used they should not take a permanent set. If you fully compress a spring and leave it that way, or cycle it for 10 years is should still return to its original length? Not so? What am I missing here?
 

James

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#2
It is my understanding that cycles are what breaks down a spring. I think if you compress a spring and leave it that way, it will be ok, but work it and it will take a permanent set.

They do wear out and I know that my manual has a wear limit spec for the suspension springs.
 

marcusgunby

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#3
A perfect spring will return every time to its set length, however in the real world they do loose length over time, ive seen cheap ones last only a few hours but most std stuff lasts years.Some people only use OEM springs for this reason.
 

NO HAND

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#4
Hi Marcus, I was wondering if recently the stock springs have a higher quality control or are they still far off their listed rate.
 
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#5
Originally posted by James
It is my understanding that cycles are what breaks down a spring. I think if you compress a spring and leave it that way, it will be ok, but work it and it will take a permanent set.

They do wear out and I know that my manual has a wear limit spec for the suspension springs.
Ahhhh creep. I should have thought about that. I had a problem like that when I had to design a polycarbonate and acrylic floor tile. There was a big difference between the yield strength that you could use for statically loaded (crap sitting on it for ever) and live loads (people walking etc.). I guess once you preload your spring it’s life it terminally doomed. What kind of stresses are we talking about that will put a permanent set on a spring? Is that the reason why people buy those plastic do-hickys to put on your forks while you transport your bike? I always thought those where so you didn’t cause fork seal leaks. Any hoo I never used them cause I thought they were a waste
 

marcusgunby

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#6
Using tie downs doesnt cause seal leaks or wear on springs.Nothing you can do to a spring will wear it out.Either its a good spring and it will last year or a bad one and it will last maybe less than a season.Dont forget these springs are designed to be used as we use them.

Seb i believe the std springs are generally close to there listed rates.Ive seen some sites say they are a long way out, but the ones ive had tested are close.Most OEM stuff is 5% i believe, i doubt many aftermarket companies can match that, however the price of some OEM springs is enough to make you wonder if its Ti you are buying;)
 
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#7
this is taken directly from tootechracing.com lot of reading but it explains the answer to your question sorry i cant post the chart but you could go to there site and check it out.

Do Suspension Springs Wear Out or Why Do Springs Break??

In our Motorcycle world springs rarely break. A well designed steel spring will basically last forever. How long a spring lasts is based on how much stress is produced in the wire when it is compressed to it's minimum length AND how many cycles (times) it will experience this load. Engineers have charts to describe how many millions of cycles a given spring material can take at a different levels of stress before they fail. (See chart below) As the stress in the wire increases, the number of cycles until failure decreases. The larger the spring wire diameter is, the less stress the wire will experience for a given spring rate. Motorcycle suspension springs use relatively large diameter wire for the loads they see in service thus they seldom experience enough stress in the wire to cause breakage. Some aftermarket companies try to use cheap wire which can't handle high stress levels without severely shortening their life expectancy. But most of these companies have seen the error in their ways and now I am not aware of any companies with chronic spring breakage problems.

The chart below is used to predict how many cycles the spring can experience before it fails. First we must determine which chart line to use. This is determined by analyzing how the spring will be used. The second picture down on the left side shows a spring cycling from no load to it's maximum load (or maximum negative stress). Our springs have almost no load at full extension so the second picture best describes the stress pattern our springs will see (from 0 to max and back to 0). This stress pattern is considered normal, so we use the standard graph marked "R=0".

The chart on the right is for some mild steel. If it were a graph of spring wire it would look similar but the allowable stress loads would be higher. The X axis (horizontal axis) on the bottom denotes the number of cycles the spring will experience before it breaks while the y axis (vertical axis) describes how much stress the wire receives during each cycle. If you follow any one of the lines you will notice that as the number of cycles increases, the allowable stress the spring wire can handle goes down. Follow the "0" line. Note that if we want to design for only 1000 cycles, our material could handle about 105,000 PSI stress in the material before it failed. If we want to design for 100,000 cycles, we can only stress the wire to 80,000 PSI. Notice that at about 500,000 cycles the line levels out at a stress level of about 75,000 PSI. This means that if we subject this material to a maximum stress of 75,000 PSI, it can be cycled indefinitely and never fail.

If a steel spring is designed properly (utilizes the proper wire size) for a given application, the spring will never experience stress levels higher than the horizontal part of the line. Thus a properly designed spring will last forever. This is a unique property of steel only. For instance aluminum, titanium, and other exotic materials continue to "age" regardless of their stress levels (there is no horizontal part of the line). Because of this constant aging, engineers must use large cross sections to keep the stress levels in the material very low. As long as the stress levels are very low, these materials can last a very long time. (Think about this as your aluminum bars get to be a few years old!!!)
 
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#8
heres the web site with the chart, the chart is near the bottom of the page

http://www.tootechracing.com/All%20About%20Dirt%20Bike%20Suspension%20Springs.htm
 

NO HAND

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#9
Cool! great info Marcus. That's interresting because the price comparison in Canada is the other way around. The Honda fork springs cost me 80$ while the race tech or most aftermarket will cost me over 120$ canadian bucks. I tought the aftermarket stuff was much better because of the surface treatment (shot peened I think?) and individual rate testing. I don't know if the OEM stuff got any of that or if it gets some other hype I don't know about. At 5% more or less the OEM stuff is good enough for me.
 
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#11
Originally posted by freestyle125


is based on how much stress is produced in the wire when it is compressed to it's minimum length
TooTech is correct in overall analysis but is confusing us with his use of terms.
Stress is the force applied to the steel, but strain is the term used to define the steel's reaction [deformation] to that force. Spring flex and spring rate is dependent upon this very small deformation [strain] of the spring wire -that is one side of the wire is compressed [it gets wider] and the other side is tensed [it gets narrower]. If the elastic limit of that particular material is exceeded -if it is deformed or strained past a certain point it, then it never returns to its original dimensions. An extremely small deformation in wire dimension affects a very large change in actual spring length. You can take a "sacked" spring, and stretch it back to it's original overall length simply by overextending it. [I hook one end to the table of my Bridgeport mill, the other end to a large bench vise , stand back and crank away. "stretch" it a bit more each time, then measure, and you'll soon have it back to it's original length. I've never had one break [yet] and get numerous seasons from the same set.
 
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#12
So who makes the best springs? I'm going to guess race tech sure as hell ain't in the runing if there anything even remotely like the rest of their products or brilliant tech support. :scream:
 
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#13
In my opinion:

Renton TI Coil springs are the best


One of the largest spring companies and the one that seems to sell the most to other companies to use who put their name on them like they made them or something is a company called Spring Maker. MANY, MANY suspensions companies buy their stuff, test it for rate, sort them out and rebox them into individual boxes and sell them like they make their own springs.


Eibach and/or Race Tech have been in the biz a long time and seems hard to call there spring products bad.


My second best is - I like the OEM Showa springs becasue they are lighter than the aftermarket springs, reasonably prices and have a wide coil spacing that has a (IMO) better frequency (not the same as TI, but a different rate like a TI springs works at). However, not sure if most riders would even feel the difference and the average public doesn't know enough about the why's and how's behind springs.

Food to chew on -- Most spring companies make springs and that is what they do ONLY. So many springs you buy are not made by the company with their name on the box. They may be made for them, but not by them.
 

DEANSFASTWAY

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#14
Sometimes springs will sag and take a set < If suspect a good idea is to measure spring when removed then If you smack a spring down sideways on like a concrete floor or table it may measure longer. you could ride it like this for a few cycles but after a very short time it will go back to its sacked length. I really like the Suzuki springs for Showa < On rears they are usually a very high quality steel and very light as stock . <On the forks (lately) It always seemed as though the outer edges of the fork springs has been polished almost shiny to eliminate some friction and less particulate contamination. New KYB shock springs seem very light. WP aftermarket fork springs always seemed good quality and looked fine finish and lightweight .Shot peening is nice but if Im doing real nice forks I like to polish the outside roughness away with a sander so it doesnt rub off. And I always do that on forks that are getting TI coat tubes. As a practice I like to try to use OEM springs if possible , Id much rather do that than use a funky spring adaptor or a crossed over spring that rubs the shock body raw. Do you guys think that powder coating springs adds to the overall rate as compared to regular paint.?? I bet it does by a bit.