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Stock spring rate #s by mr_corean
Started on: 03-26-2017 10:59 PM
Replies: 9 (388 views)
Last post by: theogre on 03-31-2017 12:11 AM
mr_corean
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Report this Post03-26-2017 10:59 PM Click Here to See the Profile for mr_coreanSend a Private Message to mr_coreanEdit/Delete MessageReply w/QuoteDirect Link to This Post
I recently put new rubber on the front of the car and the extreme drop on the front of my car was no longer driveable. I went over to the Fiero Club and was talking to sardonyx about getting some stock replacement and that lead to some curiosity questions about actual numbers. The idea being that if I wanted to go to a local race shop and pick some springs off the shelves I would be able to know exactly what to look for. Neither of us knew any cold hard numbers so I decided to get started on putting some together for the community. If anyone has any more information please post it up here and I will try to update this original post. The idea is that at some point someone in the future will google Fiero front spring rates and come across this comprehensive list that will help them out with their endeavors. The two springs sets utilized for the initial tests are both 84-87 springs, and I believe both to be WS6 which would put them both as 85-87 cars. Not 100% sure on the last statement.

A disclaimer, this is an entirely unscientific process on my part that utilizes unknown previous parts. All testing on spring rates is done through the use of a press and bathroom scale. I put the spring on the scale, zeroed it, then compressed the spring one inch, recorded the "weight" shown, compressed another inch for a total of two inches compressed and recorded again. Internet geniuses said this was acceptable way to go and a couple claiming engineering degrees laughed at the method but said it would be correct if you could be exact with your measuring. I did each test five times, threw out the two extreme ends and averaged the three middle numbers. Do with the numbers as you will as they are merely for reference.

Here is the page that sardonyx referenced me to for the different potential springs in a Fiero.
http://www.calgaryfieros.com/OSGdocs/springs.html

The springs I had, when compared to the stock ones sardonyx gave me, seemed to be from a Fiero, so that was a good starting point for at least a comparison between those 2 sets. Not knowing how different the WS6 vs non are in spring rates, the similarities between the cut and uncut springs makes me think the cut springs were also ws6 springs.

The full sized springs had just enough of a tag to be able to determine that they were off a WS6 car. My springs had no tags and my fender tag is completely washed out so no codes are visible on it.

Stock spring:
Length - 13 1/8"
ID - 3.45 bottom of spring, 3.25 top
OD - 4 7/16 bottom, 4 3/16 top
1" compression - 121 lbs
2" compression - 235

Cut spring
Length 11 11/16
ID - 3.41 bottom, 3.29 top
OD - 4 3/8 bottom, 4 1/4 top
1" compression - 129
2" compression - 224

Pictures of scale with different springs as well as a shot of the two for length comparison.

Full Length, 1"


Cut 1"


Cut 2"


Cut vs Uncut


Car with uncut, 245/40-18



Car with cut, 235/40-18, .3"difference in tire diameter


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olejoedad
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Report this Post03-27-2017 07:26 AM Click Here to See the Profile for olejoedadClick Here to Email olejoedadSend a Private Message to olejoedadEdit/Delete MessageReply w/QuoteDirect Link to This Post
At one time there was a very comprehensive thread on the Forum that listed all of the data you are seeking.
I'm sorry I don't recall who started it, or the name.
Perhaps a Google search would turn it up.
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pmbrunelle
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Report this Post03-27-2017 08:15 AM Click Here to See the Profile for pmbrunelleClick Here to Email pmbrunelleSend a Private Message to pmbrunelleEdit/Delete MessageReply w/QuoteDirect Link to This Post
With your test, you are not accurately simulating the perches in the car. In the car, the perches are more "form-fitted" to the end of the spring. Here, the wires are sitting against flat surfaces. With low loads, the ends haven't quite yet taken the shape they will have at normal (much higher) loads.

This is not necessarily a bad thing... if we want others to be able to reproduce your test results, the experimental setup must be simple and easy enough for anyone else to duplicate.

However, to minimize this "end-deformation error", calculate the differential in force it takes to deflect the spring one inch.

Example using your stock spring numbers:

0 inch -> 1 inch compression
0 lbs -> 121 lbs
Differential spring rate = 121 lbs - 0 lbs = 121 lbs/in

1 inch -> 2 inch compression
121 lbs -> 235 lbs
Differential spring rate = 235 lbs - 121 lbs = 114 lbs/in

Ideally, you would measure the differential spring rate at ride height; this would give the most meaningful results. E.g. if at ride height there is 4.3 inch of compression, measure the differential spring rate from 3.8 inches to 4.8 inches.

Unfortunately, you will probably reach the limit with your bathroom scale...

But the closer you can get to ride height, the better. 2 -> 3 inches would be better than 1 -> 2.

Remember to tare the weight of the spring before starting.

Another source of error I noticed: part of the spring is overhanging the cross-bar on the press, so it is supported on one side only. Therefore, it will want to bend like a banana. Try to center it within the cross-bar.

A note on safety: I would suggest passing a steel wire through some of the coils, as in extension springs for garage doors. If the ends slip, the spring will want to shoot sideways... which could be quite painful to someone! So a wire tied to the press could stop the spring from flying too far. However, if the wire gets pinched between the coils, the test results are invalid.

The fact that the spring is bending like a banana will tend to shoot the spring out.

[This message has been edited by pmbrunelle (edited 03-27-2017).]

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Report this Post03-27-2017 08:40 AM Click Here to See the Profile for fierosoundClick Here to visit fierosound's HomePageClick Here to Email fierosoundSend a Private Message to fierosoundEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by olejoedad:

At one time there was a very comprehensive thread on the Forum that listed all of the data you are seeking.
I'm sorry I don't recall who started it, or the name.
Perhaps a Google search would turn it up.


Maybe this one: //www.fiero.nl/forum/A...050119-2-054238.html
oops... this is only 88 info...


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[This message has been edited by fierosound (edited 03-27-2017).]

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Blacktree
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Report this Post03-27-2017 08:47 AM Click Here to See the Profile for BlacktreeClick Here to visit Blacktree's HomePageClick Here to Email BlacktreeSend a Private Message to BlacktreeEdit/Delete MessageReply w/QuoteDirect Link to This Post
mr_corean, where did you get that hood vent?
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Report this Post03-27-2017 08:57 AM Click Here to See the Profile for fierosoundClick Here to visit fierosound's HomePageClick Here to Email fierosoundSend a Private Message to fierosoundEdit/Delete MessageReply w/QuoteDirect Link to This Post
I documented some springs I have here:
//www.fiero.nl/forum/A...120111-2-110727.html

I got lowering spindles in my GT, but I needed to replace my cut springs and raise the front.
//www.fiero.nl/forum/A...120111-2-110255.html

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mr_corean
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Report this Post03-29-2017 07:16 PM Click Here to See the Profile for mr_coreanSend a Private Message to mr_coreanEdit/Delete MessageReply w/QuoteDirect Link to This Post
pmbrunelle, you bring up some good points, some of which were addressed.

I thought about what you mentioned with the "end-deformation error" but I'm not sure it is as great as one would think. The only thing I am basing that on is the shape of the rubber end caps that the springs rests in on the perches. If the spring actually flattened out at the bases the end caps would be flat. Since they have a shape that follows the spring unwinding though, it led me to believe that the error is not as much as I would initially have assumed. This is of course just me making an assumption off the shape of a very unimportant part. However, it is why I have the scale rating at 1" and 2". Just in case the first inch is not entirely accurate do to the spring taking shape.

I agree with your assessment that the force needed to compress the spring from one point to another is what is being measured and another reason why I included the 1" and 2" readings. Unfortunately to get to a 3" reading would have been beyond the capability of my scale. With a standard cylindrical spring with evenly spaced coils the pressure needed to compress the spring an additional inch will remain constant. If it takes 100 lbs to compress it one inch it will take 200 pounds to compress it 2 inches. Our front springs fit this bill. Don't quote me on this, but I don't think our rear springs completely do because of the slight shape change at the ends of them. I know that a spring that tapers significantly or has coils tighter on end than the other has different spring rates depending on how far the spring is compressed. Because of my use of old springs and unscientific measuring devices I am satisfied with my conclusion that the front spring rate on these particular springs is about 125psi.

I thought about the banana thing too. I moved the scale around a bit to try different angles and added a block in to clear the dial and a few other things. All results were within a couple pounds of each other so I came to the conclusion that I was not compressing the spring enough for that to become a significant enough issue to be a factor.

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mr_corean
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Report this Post03-29-2017 07:18 PM Click Here to See the Profile for mr_coreanSend a Private Message to mr_coreanEdit/Delete MessageReply w/QuoteDirect Link to This Post

mr_corean

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Member since Mar 2005
 
quote
Originally posted by Blacktree:

mr_corean, where did you get that hood vent?


DoubleC4 here on the forums. I highly recommend everything from that man! I have his front c5 rear c4 brakes on the car and had his flush headlights on before as well. Only reason I changed those out was because the pop ups flowed better with Lotus nose.
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Report this Post03-30-2017 04:08 PM Click Here to See the Profile for BlacktreeClick Here to visit Blacktree's HomePageClick Here to Email BlacktreeSend a Private Message to BlacktreeEdit/Delete MessageReply w/QuoteDirect Link to This Post
Thanks for the info.
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theogre
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Report this Post03-31-2017 12:11 AM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreEdit/Delete MessageReply w/QuoteDirect Link to This Post
Note that OE spring rate for back is not simple as above because OE rear springs are Progressive springs. (Above spring is Simple aka Linear type.)
Simple test above will lie using w/ any Progressive types.

Progressive can mean different # of coils, different diameters, or both for each area of spring.

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