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Author Topic: How to determine spring rate by looking at a spring  (Read 22112 times)
mackie-bros-racing
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« on: March 09, 2010, 01:01:25 PM »

Hi,

I have several springs I have inherited that have no markings on them to indicate what their spring rate is (85, 90, 105, etc).

Is there a way to determine the spring rate without any test equipment?

Such as...

Counting the turns  (ie 5.5 turns = 100# spring)

Measuring deflection when weigted be dead weight (ie put a 50# weight on it and see how far it compresses)

Also, what does the weight value of a spring mean (ie is 85# mean that 85 lbs of weight on a spring will deflect it 1 inch?)

Thanks,

Mark Mackie

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Mark Mackie
sfreitas20
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« Reply #1 on: March 09, 2010, 01:21:07 PM »

Hey Mark,

Here is what I was told when I asked this question when we first started in the sport.  It does require a drill press and a scale, so it isn't totally answering your question about without any special equipment.  Place a scale on a drill press and then put the spring on the scale and zero it out.  Next, use the drill press to compress the spring 1".  What the scale reads is your spring rate.

I guess if you had enough weights, you could pile them on the spring until you compress it 1" and then how ever much you had on it would be your spring rate.  However if you choose this option, watch your toes!!! Smiley
« Last Edit: March 09, 2010, 02:49:22 PM by sfreitas20 » Logged

Scott Freitas
Patriot Motorsports Inc.
Swartz
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« Reply #2 on: March 09, 2010, 01:58:37 PM »

I have used the drill press and scale method and it works ok for a ballpark. It is only as accurate as the scale you use and the inch you measure. It is important to check the springs in the light classes, I think, because there are tollerances in marking the springs. On some as much as + or - 2lbs. You could have a problem out of nowhere if you replace a 102lbs spring with a 98lbs spring thinking they were both 100lbs springs.
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Swartz
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« Reply #3 on: March 09, 2010, 02:44:49 PM »

Anyway, I didn't really answer the question. The spring rate is weight over 1 in. compression. The only way to measure a spring, other than a compression test, is to know the material used and the wire diameter and do the math. A spring rate checker is a whole lot less bother.
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miketsmith
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« Reply #4 on: March 09, 2010, 05:49:47 PM »

Where can you buy the tool, a good one.
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Swartz
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« Reply #5 on: March 09, 2010, 06:36:56 PM »

Here is a link to one for just under a grand:

http://www.pegasusautoracing.com/productdetails.asp?RecID=1215

It would be a lot cheaper to make friends with one of the big car teams in your area that has one or send them to a spring manufacturer to get them rated. A good spring checker is not considered "portable" and can cost up to $8,000.
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crew chief
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« Reply #6 on: March 09, 2010, 06:56:22 PM »

You can buy alot of springs for $800/$900, so why buy a checker
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Swartz
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« Reply #7 on: March 09, 2010, 07:02:07 PM »

 Cheesy Good point! As long as the springs are marked.
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miketsmith
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« Reply #8 on: March 09, 2010, 08:07:26 PM »

Who makes the best and true spring? I have used Advance but I am sure there are others.
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sfreitas20
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« Reply #9 on: March 09, 2010, 08:38:48 PM »

We use zero error and tanner springs and haven't had any issues.
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Scott Freitas
Patriot Motorsports Inc.
sprintcar39
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« Reply #10 on: March 09, 2010, 10:05:02 PM »

I have a Tanner spring tester that I can bring to the North Carolina race in a couple of weeks and you can check all the springs you want.
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Eric Rankine
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USAC National Midget - Spike/Esslinger
GAQMRacers
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« Reply #11 on: March 09, 2010, 11:17:36 PM »

Mark -- in case you're not going to the USAC race in NC -- check with Terry Mathis.
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dmmc
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« Reply #12 on: March 10, 2010, 02:52:30 PM »

Dave? Creech from Michigan had a used Tanner spring rater for sale at the Columbus Indoors.  It seemed like it was priced pretty reasonable.  I don't really know how to get ahold of him though.  I pretty much use the drill press / scale method as well.
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sprintcar39
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« Reply #13 on: March 10, 2010, 03:06:48 PM »

Dave Creech - dcreech@ford.com
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Eric Rankine
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philabenroth
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« Reply #14 on: March 22, 2010, 10:31:19 PM »

two scales, dial indicator, press.

one scale placed on top of the other, zero them both, compress and measure one inch with the dial indicator, read the scales and compare the two scales to accept or deny their variance from one another.

Even if you don't have high accuracy electronic scales but have repeatable scales, the information will always be good, as it is all relative. If your scale reads 80 lbs when it should read 85, it doesn't really matter because you'll have all your springs measured and when you want to go up or down in rate, the measurements are relative to one another.

We have springs from a number of different manufacturers, and the way they're measured from their manufacturer varies from one to the next, and contrary to some opinions I've heard, springs do lose their rate over time due to fatigue, so the material and thickness aren't necessarily a precise method.

Tanner's rate checker is likely the easiest and most cost effective checker if you don't want to go to this trouble.

Phil Abenroth
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