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Old 05-03-2010, 10:35 AM   #1 (permalink)
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Who to calculate what CO spring rate you have

I have some CO springs (2.5 id) various lengths, and there are no numbers to indicate what rate they are. I've searched and read BV's CO bible 1&2. How can I figure out what rates these are?
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Old 05-03-2010, 11:35 AM   #2 (permalink)
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in order to do it correctly, you need a spring compressor or press of some sort. you need to compress the spring 1", and what ever amount of force it takes to get 1" is the spring rate. so if it takes 400#s to crush a 3"x16" spring to 15", its a 3x16x400
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Old 05-03-2010, 11:48 AM   #3 (permalink)
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The description of how to do it based on the dimensions of the spring is in Part 1.

You can also do it by applying a known force (weight) and measuring the deflection (easiest if done vertical (perpendicular to earth's surface) so you don;t have to factor the IR.
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Old 05-03-2010, 12:28 PM   #4 (permalink)
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Let me clarify better what I am asking:


Quote:
Originally Posted by BillaVista View Post
The description of how to do it based on the dimensions of the spring is in Part 1.

You can also do it by applying a known force (weight) and measuring the deflection (easiest if done vertical (perpendicular to earth's surface) so you don;t have to factor the IR.
I did read this, an excellent tech article as always...Thank You! And I understand as well as my limited capacity will allow me.

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in order to do it correctly, you need a spring compressor or press of some sort. you need to compress the spring 1", and what ever amount of force it takes to get 1" is the spring rate. so if it takes 400#s to crush a 3"x16" spring to 15", its a 3x16x400
This was also laid out in BV's article.

What I want to know is what PRACTICAL way can I do this without any calibrated measuring devices. I mean stacking 300 lbs on top of a spring is not going to be that easy. I don't have access to a press of spring compressor with any calibrations.
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Old 05-03-2010, 01:05 PM   #5 (permalink)
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You don't need to be that scientific about it.

Find something that you know how much it weighs, put it on the spring, measure the deflection.

Hell, put the spring in a doorway and stand on it yourself. Use the door frame to balance while someone else measures the spring. Good enough for a ballpark estimate anyway.
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Old 05-03-2010, 01:43 PM   #6 (permalink)
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Originally Posted by vetteboy79 View Post
You don't need to be that scientific about it.

Find something that you know how much it weighs, put it on the spring, measure the deflection.

Hell, put the spring in a doorway and stand on it yourself. Use the door frame to balance while someone else measures the spring. Good enough for a ballpark estimate anyway.
How far does it need to compress to get a somewhat accurate estimate. For example if I (220 lbs) stand on one of the 16 inch 2.5 spring it compresses about 1/2 inch. Does this mean its a 440 lb spring?
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Old 05-03-2010, 01:51 PM   #7 (permalink)
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Of course the answer is only as good as the info used to arrive at it, but yeah, that's what you'd do.

The spring rate should be linear - i.e., a 440 lb/in spring takes 220 lb to compress half an inch, 880 lbs to compress two inches, etc.
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Old 05-03-2010, 10:32 PM   #8 (permalink)
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If you have a set of calipers you could just use the equation from the same article (and in the spreadsheet) and calculate it. Nothing more than a couple of measurements and count the number of coils. It worked great for my springs before I found the markings.
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Old 05-03-2010, 10:42 PM   #9 (permalink)
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Crude way but it should work. I used my race car scales but a good bathroom scale should do it. With floor jack lift truck up. place spring between bumper and scale. slowly lower truck on spring till you get 1 inch of compression read scale. Thats the rate. If you max out scale compress only 1/2" and double weight reading. This should get you in the ballpark.

Oh and if it shoots out it hurts...
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Old 05-04-2010, 07:29 AM   #10 (permalink)
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Next time use a dremmel and mark the spring rate on both ends before installing them...or just buy King springs because that is how they mark all theirs.
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Old 05-04-2010, 02:31 PM   #11 (permalink)
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Quote:
Originally Posted by TPIJeep View Post
Crude way but it should work. I used my race car scales but a good bathroom scale should do it. With floor jack lift truck up. place spring between bumper and scale. slowly lower truck on spring till you get 1 inch of compression read scale. Thats the rate. If you max out scale compress only 1/2" and double weight reading. This should get you in the ballpark.

Oh and if it shoots out it hurts...
I will try this, and hopefully not kill myself.
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Old 05-04-2010, 02:33 PM   #12 (permalink)
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Quote:
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Next time use a dremmel and mark the spring rate on both ends before installing them...or just buy King springs because that is how they mark all theirs.
I bought these used and was told the spring rates were xxx, unfortunately when mounted one side sagged alot more than the other, after close inspection you could see that two springs were not the same. (the numbers were worn off when I got them)
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