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Old 12-30-2012, 09:15 PM   #1
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Default How to tell the difference between springs if you don't know the color?

Hi guys,

Can someone show me how to tell the difference between springs (which one is harder/softer) other than squeezing them by feel? For instance, I currently have an HPI pink and gold spring but cannot tell the difference between this 18 lbs/in spring vs. 19 lbs/in spring, respectively. So if the small dab of pink and gold color that they put on these springs wear off, how can I tell which is which when I have A LOT of other color springs?

Crudely, I can get a set of weights, somehow balance and put them on the spring and then measure the deflection. But this would just tell me which spring is harder than the other. For the "HPI pink" spring, for example, which is supposedly 18 lbs/in, I should be able to put 18 lbs on it and see that it compresses 1 inch (25 mm). But this spring is only about 1 inch long to begin with. It fully compresses to 3/8 inch. Thus, the deflection is only 5/8 inch. so this tells me that I can't even test the fact that this spring is 18 lbs/in using an 18 lbs weight since I don't have enough spring length to compress... See my dilemma?

Is there some sort of tool out there that I don't know of?

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Old 12-30-2012, 09:37 PM   #2
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Rather than squeeze each spring seperatly, easiest option is to put one against the other, then squeeze against each other. The one to compress first is the softer, see picture.. quick and simple

Other option, measure the wire and coil count. HPI's have a 1.5mm wire, Golds have 6 coils, Pinks have 6 1/4, Silver 6.5 (blues are an odd ball with 1.4mm/6 coils)

General rule of thumb... thicker wire and/or less coils = harder spring.

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Old 01-01-2013, 09:42 PM   #3
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Hmm... that's a darn good idea. So this will definitely tell me which is "harder" and softer. But is there a tool somewhere that will actually give me the "value" (i.e. - 18 lbs/inch, for example).
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Old 01-01-2013, 10:21 PM   #4
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Use a set of calipers to measure the thickness of the wire, unless I'm mistaken they should be different by a few thousandths... at least that's how I have to tell the difference with Losi touring springs.
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Old 01-01-2013, 10:47 PM   #5
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That will kinda work as well but if you start using different brands with different number of coils + different thickness wire it may be hard to work out. I have always used the same method described by Ed, 2 springs back to back. 1st one to compress is the softer spring. No tools required either!

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Old 01-01-2013, 11:25 PM   #6
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Quote:
Originally Posted by M3Armand View Post
Hmm... that's a darn good idea. So this will definitely tell me which is "harder" and softer. But is there a tool somewhere that will actually give me the "value" (i.e. - 18 lbs/inch, for example).
Yup, it's called a spring dyno. I believe integy (amongst other manufacturers) makes one.
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Old 01-02-2013, 10:12 AM   #7
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There is a spring rate calculator in the RC Crew Cheif program.
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Old 01-02-2013, 10:38 AM   #8
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Quote:
Originally Posted by DesertRat View Post
Use a set of calipers to measure the thickness of the wire, unless I'm mistaken they should be different by a few thousandths... at least that's how I have to tell the difference with Losi touring springs.
Is correct. Its the gauge of the spring tells you the the action of it. Colors a fast referance to tell instead of guessing.
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Old 01-02-2013, 07:51 PM   #9
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Spring rate is determined by:

-Number of active coils
-Mean diameter
-Wire Thickness
-Modulus of rigidity (same for 99% of the springs)

You can calculate it here:

http://www.engineersedge.com/spring_comp_calc_k.htm
http://www.engineersedge.com/calcula...ring_k_pop.htm

How to determine the amount of active coils: http://springipedia.com/compression-counting-coils.asp
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