Springs in general...

canyncarvr · Post by **canyncarvr** » 05:00 pm Apr 25 2005

Given: Two fork springs, same length. Rates unknown. Well, one is, but for the purpose of the question, say it's not.

One spring has 28 coils, one has 31. The wire thickness is the same on both springs.

Is this a true statement?: The number of coils does not necessarily have anything to do with the rate of the spring.

If that is true..what difference DOES it make? The spring with the fewer number of coils could be compressed further before it got to coil bind..but that's not an issue in a fork. IF the two springs happen to be the same rate is there an advantage of one number of coils to the other?

Thanks, folks!

Post by **Indawoods** » 05:06 pm Apr 25 2005

It seems to me CC that the one with more coils would disperse the load or energy over more surface area than the one with fewer coils.... meaning what? I don't know... maybe longer life? Smoother action?

skipro3 · Post by **skipro3** » 05:53 pm Apr 25 2005

Imagine you take this to a further extreme: keep removing 2 coils while keeping the same spring rate. What do you end up with?

canyncarvr · Post by **canyncarvr** » 06:03 pm Apr 25 2005

K=G x d4/8 x D3n

Where
G: modulus of rigidity (shear modulus)
d: diameter of spring wires
D: diameter of spring coil
n: number of active coils (see below)

This formula shows that while the number of coils does figure into spring constants:

http://www.engineering.com/content/Cont ... d=41005011

...it really doesn't mean anything if you don't know the shear modulus. Ain't gonna get that info from looking at a spring.

Inda: I was thinking along the same line, but don't know and is why I asked the question.

I've got two different springs..one is supposed to be a RaceTech .38. The other measures (with the sorry bathroom scale measuring method) to be about a .38 or .40. Heck..with only 1lb/in difference between the two, it's kind'a hard to tell.

IF they happen to be the same rate, I'd rather have more coils. ...I think....

No one 'round here has a tool to measure spring rate. Not that I've found, anyway.

I thought I'd put 'em both on a stick at the same time, compress them a couple inches and then measure their individual length. That would tell me if they were the same rate.

..wouldn't it?

**edit**

Ski:
You end up with two springs of the same rate but of differing capacity...as long as it's a given that the rate is the same.

Of course, that isn't going to happen if you start out with two springs that are the same rate and start removing coils from one of them. Do that, end up with four coils on one, thirty on the other and the rate isn't going to be 'the same' any longer.

Ha! Try putting 21# of force on four coils cut off a .38 spring. Bet it don't compress an inch!

I think there is commonly a misunderstanding of rate vs: capacity.

Don't know about spring linearity, either. They're supposed to be linear (talking about a straight rate spring), but somehow it seems reasonable to me that they would increase somewhat in rate the more compression.

I am quite sure of one thing. I have a lot of commonly held misunderstandings myself!

Post by **Indawoods** » 06:10 pm Apr 25 2005

OK CC... I'll bite... How did you end up with two different springs? Did your KX front end come this way?

canyncarvr · Post by **canyncarvr** » 06:20 pm Apr 25 2005

By taking one from two diifferent sets of springs. My 'given' at the top didn't say I was talking about one set

bradf · Post by **bradf** » 06:43 pm Apr 25 2005

CC, the variables you listed are what makes a spring...spring. When I was involved in IMSA and NASCAR, I tested each spring before it went on. The reason was that even a spring from a very well established company could be off by as much as 5%, which was too much for dialing in a suspension. Sometimes the error was due to the spring being bent because of a wreck. Usually it was just off. It didn't have to be out much to be off. Evenly wound coil springs are very linear. To sum it up, you can either trust the manufacturer to be close, or test them yourself. Put the spring inside a PVC pipe slightly larger in diameter and set on an accurate bathroom scale and zero the scale. Using a push rod like a wooden dowel, push down until the spring compresses 1 inch and read the scale. These springs are rated kg/mm so there will have to be a conversion from lbs/inch.

canyncarvr · Post by **canyncarvr** » 06:58 pm Apr 25 2005

Understood. Your method is better than mine. I used a guide rod on the inside of the spring as opposed to a guide on the OUTside. Thanks!

Problem is telling the diff between a .38 and .40 (21.2/22.3lb/in as I recall the numbers) on a bathroom scale. Well..on my bathroom scale anyway. That's ok! It's probably as accurate as it is readable!

So...you know much more about springs than I'll ever forget..what about the number of coils? Which one would be preferable? Does it matter?

Thanks for the input!!

BTW...the .kg rating multiplied by 2.2 (kg/lb) multiplied by 25.4 (mm/in) gets you the pounds/inch number.

I think. Didn't check it...but anyone can tell me how wrong I am if'n they wanna.

Post by **KDXGarage** » 07:32 pm Apr 25 2005

IF!!! they both have the exact same outer diameter and thickness of individual coils, then the one with less number of coils is a stiffer rate.

skipro3, if you keep removing two coils and have the same spring rate, that would be one thin ass coil diameter spring at some point.

GIVEN that you are handing out math word problems, give us all the measurements next time.

If you want an extreme example, think of a shock spring vs. a fork spring: many more coils on the fork spring, but smaller diameter coils and spring, whereas the shock is thick coils and diameter of spring, but shorter height (number of coils).

bradf · Post by **bradf** » 11:00 pm Apr 25 2005

Number of coils and for us doesn't matter. As long as there is no coil bind. All that matters is accuracy and that both (forks) are the same. The best manufacturers make the lightest spring possible for the least un-sprung weight. I am sold on Eibach as I have found their springs the most precise. This is an area where all we have to do is get the best rate spring for our riding style and then pre-load it correctly. But then there is the airspace (oil level) in the forks and the nitrogen charge in the shock. I tried progressive springs once in my XR250, hated em! Hard bumps would shoot through the soft section so fast that the forks would go waaay into the stroke very soon.

canyncarvr · Post by **canyncarvr** » 10:45 am Apr 26 2005

The set of Eibachs I tried failed. One of 'em lost about 3/8" in length in three rides. Doesn't make Eibachs 'bad' I guess. Just something to keep in mind...sometimes 'stuff' just happens.

re: both forks the same.

I think I recall some fork setups that were designed with very different springs in each leg? While it's not different springs...my Honda's 'Trac' system changes the compression valving on one fork when you hit the brakes. Certainly seems to me that both legs should be the same, but some injuneers evidently aren't restricted by such thought.

A good lot of KXs come with progressive springs. A good lot of folks say, 'Take 'em OUT!!'

re: 'IF!!!...the one with less number of coils is a stiffer rate.'

Just 'cuz they are the same measurement doesn't mean they are made of the same metal. Surely spring stock isn't all the same?

bradf · Post by **bradf** » 11:01 am Apr 26 2005

it is true that not all spring wire is the same. Just like any steel, it it how much carbon is put back into the steel then how it was cooled and how/when it was rolled into wire. Valve spring companies like Crane, Comp etc really have exact specs and those springs are under a tremendous load (load not only being the much higher rate but also the movement speed and temps). Only a steel mill can make steel springs, the spring makers only shape it. So it's up to the mill to produce the quality and the makers to ensure it.

Post by **KDXGarage** » 01:22 pm Apr 26 2005

OK, throw in another variable. Since you seem to be mostly concerned with spring A vs. spring B, here's what you can do. Grab a broom handle. Slide the spring over it, add x pounds of workout weights, measure difference in free spring length and compressed length. Do the same for spring B. Compare those numbers to see which is stiffer / weaker.

Any proof they were Eibach springs?

Eibach 996 model springs (the ones in KDX's among others) are 510mm long and come in odd numbered rates. I have read you state them as .40's and somewhere around the 470mm - 472mm length. Since you were dealing with MX - Tech and they reportedly used SprinMaker springs and currently advertise that they do, I am still thinking you got some SpringMaker springs. They are 470mm or 472mm. You can look on http://www.cannonracecraft.com to check the length. Now here's the seriously ribbing you part. You must have made a mistake and let some Bel-Ray H1R touch them.

OK, I am through messing with you.

If all else fails, test ride pair A, then B and see which one you like better.

canyncarvr · Post by **canyncarvr** » 03:17 pm Apr 26 2005

Like this?

I thought I'd put 'em both on a stick at the same time, compress them a couple inches and then measure their individual length. That would tell me if they were the same rate.

Wilkey said they were Eibachs. This was well before anything SpringMaker was going on with MX-Tech.

No. I have no proof. It's what I was told.

You know...I'll bet you're right about the H1R part!!

re: If all else fails, test ride pair A, then B and see which one you like better.

That's what's going to happen I'm sure. I had to have bought 'em for SOME reason!

Post by **KDXGarage** » 03:27 pm Apr 26 2005

470-ish and .40 rate Eibach's, he must have had em like special ordered

Get those forks on that bike and stop worrying about em.

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Springs in general...

Springs in general...