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Spring Rate Data


May 24, 2003
38? 27' N 75? 29' W
Starting the spring thread that was requested.
I will edit it as we go, adding numbers and deleting extraneous comments.
Please comment, and please offer to loan sets of springs if you remove KNOWN OE springs to change anything. I would also test any lowering or overload springs you can loan me.
I'm at the south end of Delaware, and can meet somewhere else if we can work it out.

Quotes from another thread:

I did all the springs a long time ago and found varying results. The first numbers posted above were probably from measuring the wire plus paint. I do remember a wagon rear spring being around that number. Then I lost that notebook.

Since I couldn't find any numbers, I started over.
I just measured the springs from a mid-80s CT 244 that went to the crusher.

Front Springs 80 lb/inch.
Rear Springs 91 lb/inch.

Scraped off the paint and undercoating, measured, did the math. Pretty close.
Maybe that wagon with 117# had overloads, but 117 and 107 aren't that far apart. Plus the 117 might have been measuring and using a calculator.
And maybe the 120# fronts that were mentioned were GT or Diesel springs. I really wish I had the diesel springs I got rid of.

I measured how much pressure it took to compress each spring, and retested each run. Then I increased the pre-load, so I got numbers starting at 40, 50, 60, 70, 80lbs. That's TEN tests per spring.

I will have turbo wagon (US) from the junkyard as soon as I have the money to pay for the front suspension. Until then, nobody has offered to let me test any springs at all. I do what I can.
I'll test another mid-80s sedan soon, and also a non-turbo 940 wagon.
(I paid for the suspension, haven't seen it yet in the several months, even when I told him to drag it here and let me remove it.

Mike, sticky somewhere?
Done. At least, it's a start.

Yesterday I tested 1992 wagon rears. They were a little off side to side.
One was 97 pound/inch, one was 107. Looking for another set.

I have another 240 sedan that I will test soon, and I will try to get these fronts tested. Had some issues with a brake line, and it's changeover day for the exploratory class.
so, just measured numbers:

1988 Hartford CT 244
Front springs 80 lb/in
449mm (17-5/8") free length
166mm overall Diameter
13.2mm (.520") wire diameter
5.5 free coils
11.5" installed height hanging
8.5" installed height sitting

Rear 91 lb/in
415mm (16-3/8") free length
129mm overall Diameter
11.85mm (.466") wire diameter
7.5 free coils
15.25" installed height hanging
12.25" installed height sitting
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92 245
Front springs 79 and 80 lb/in
445mm (17-1/2") free length
167mm overall Diameter
13.6mm (.540") wire diameter
5.5 free coils
___ installed height

Rear 97/107#
449mm (16-5/8") free length (will recheck)
129mm overall Diameter
13mm (.510") wire diameter
8 free coils
___ installed height
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added numbers, separated into posts.
If there's an inch with fractions, it was a tape measure. If a decimal, it was a dial caliper.
I scraped off the paint with a knife for the wire dia.

I did not use math to get the rates. I used a scale and a dial indicator on a compressing fixture.
When I have time, I will go to NASCAR-land with some springs to see how close my rig was.
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old IPD sport black springs from Mike Rausch.
I will add pics later.
Only measured one each.

Front spring 137 lb/in
330mm (13") free length
6.5" overall Diameter
14.27mm (.562") wire diameter (paint rubbed through)
4-1/8 free coils
___ installed height

Rear 148#
343mm (13.5"") free length
5" overall Diameter
12.7-12.8mm (.500-.505") wire diameter (varies, did not clean off paint)
6 free coils
___ installed height

Should ride like **** with the 1.5:1 motion ratio squared in back.
Rear vert rate would be 222lb/inch.
Front you lose a little, so 130-ish.
If I had that much rate out back I'd want at least 250 in front to keep it from pitching.
Taking the IPD springs and the wagon springs to NASCAR-land for checking on Sunday. That way I will know how far off my rig is. I may also purchase a load cell to replace my freight scale.
hit "post" too soon. hang on a minute..

I took 2 sets of springs to Drew for testing. Both have been tested on my home-made rig.

1992 245 springs, one of the rears was lower than the other, possible changed to a sedan spring. I took the higher of the two.

Early (244?) IPD Sport Springs, borrowed from Mike Rausch.

IPD rear, waiting to be molested.

Waiting for the computer to get its head together.

Stuff to make things stiffer on the fly. Everything gets tested, and springs stick around the longest of any NASCAR team part.

IPD front on the right, fancy coilover stop spring on the left. That's what it rides on at high speed.

Gross adjustment slider clamp bolts

Talking smack to the program, telling it what it needs to do for us.

You have to put in measuring blocks to let the machine measure the height of the retainer/spacer the spring will sit on.

Like SO.

But IF you forget, (and it seems someone did) and hit it with a load instead of clicking the right "test", this might happen:

Test complete. But what does it mean? 150 lb/in for the rear, but wait. There's more!

Avg. pressure, including harmonics and cell noise and ****.


Next up, IPD front.

Test #2 complete, with Test #1 graph behind it. 146 lb/in. Might as well call that another 150.

Test #2 graph.

Front 245 time.

Poncy little 95 pounder.

The low start is due to the imperfect tail in the seat.

You could call this a 100 lb/in spring.

Rear 245 time.



Front and rear 245 overlaid.



IPD rear and stock wagon rear compared.

IPD front and 245 front compared.
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My first round of tests, I used wood to spread the load on my scale (an old shipping scale with springs inside, sheet steel housing, dial indicator).
Follow-up tests to compare my methods with Drews, I used a steel plate (old rail/tie connector) but with wood on top.
Where I was off 10-15# before, this time I was much closer.

I plan to buy a load cell to see if I can improve more.

I will take 240 sedan springs and 740 wagon springs down next time, and any other springs I can get my hands on.
Are the IPD springs you tested wagon version or sedan? I missed it if you specified. I was thinking they might be the wagon version looking at that rate.

Thanks for this Mike!