spring rate

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scheckaet
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spring rate

Post by scheckaet »

Is there an easy way to figure out the spring rate for front fork?
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canyncarvr
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Post by canyncarvr »

Measure it.

Whew...that was easy!

Considering you don't have a decent spring scale (else why would you ask the question) you can use a bathroom scale.

Rig up some jig that will allow a spring compression of 1". Ex: Cut a piece of PVC that has a diameter large enough to slip the spring into 1" shorter than the spring. Put it on the scale, compress the spring just to the point the end of the spring is level with the pipe.

There's yur number (on the scale).

Other methods with the same end in mind obviously give you the same result. Say...put a piece of dowel INside the spring. Either cut to length or (easier) make marks on the dowel. Compress using a 1" piece of PVC to the mark...samo samo.

A good scale will measure 1/10ths of a pound easily. Take reasonable care in making your measurement tools and the rest is simple math (to get to kg/mm from lb/in).

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Jeb
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Post by Jeb »

Another option (if needed; CCs will certainly work) - hang a light weight from the spring. Measure the difference in spring length with the weight. Convert your weight/distance to kg/mm and there you go.

As long as you don't get crazy with the weight the spring rate will be the same for a slightly stretched spring as a slightly compressed spring. Since it's a spring from the forks you're talking in the neighborhood of .4 - .5 kg or close to a pound (per mm of movement). So, for example, a 5 lb weight = 2.273 kg that stretches 5mm would mean a spring rate of 0.455 kg/mm.
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canyncarvr
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Post by canyncarvr »

Can you hang the bathroom scale from the spring...??? :hmm:

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Jeb
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Post by Jeb »

>|<>QBB<
Jeb wrote:Another option (if needed; CCs will certainly work) - hang a light weight from the spring. Measure the difference in spring length with the weight. Convert your weight/distance to kg/mm and there you go.

As long as you don't get crazy with the weight the spring rate will be the same for a slightly stretched spring as a slightly compressed spring. Since it's a spring from the forks you're talking in the neighborhood of .4 - .5 kg or close to a pound (per mm of movement). So, for example, a 5 lb weight = 2.273 kg that stretches 5mm would mean a spring rate of 0.455 kg/mm.
20lb would be a better weight - much better resolution than 5lb . . .

RE: hanging the scale by the spring - I suppose, and if you had negative numbers on the scale the scale's all you need (I think that's where you're going) . . . but the real question is this: how many cartons of clove cigs would it take to deflect a 0.41 kg/mm spring by 10mm? :wink:
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Post by canyncarvr »

Agreed: Whether extending or compressing a given rate spring, the rate will generally apply.

But..given as the environment of the spring is compression and compression is the only consideration in regard to its use, I vote for measuring via....compression.

I wouldn't want to try to measure the extended spring and have to come up with any 1/2 fast reasonable precision. Them mms are teeny little things...1/16's of an inch are bad enough! 5mm isn't even a 1/4"!

Besides that...the weight used would fall out of its jerry-rigged attachment and fall smack dab on your toes!

You can, however, cut a piece of PVC, dowel..whatever to a quite exact measurement.

Re: How many?

A LOT. It's time to reorder!!

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scheckaet
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Post by scheckaet »

Sounds much easier than I expected. kool
Thanks y'all
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