I need to know the stock spring rates on my '88GT. I've searched, but I can only find this chart:

1988 ALL CODE
---------------
10048402 FPJ (Stiffest)
10048401 FPH |
10068654 ARD |
10068653 ARC |
10068652 ARB (Softest)

Can anyone put actual rates to these codes?

Neil

Ive never heard of the FPJ and FPH springs, relative to an 88.
Also, the last three in the list are front springs.
The rears were tagged PUB, PUC and PUD, from softest to stiffest.

I haven't been able to figure out any rhyme or reason for which springs came with which cars. (My Formula came with PUC springs, while my base coupe came with PUD (stiffer) springs. I also found a discrepancy between the RPO label (indicated PUC) and what was actually in the car (PUD). I don't have any reason to suspect that the previous owner(s) would have changed them.
Just a bit of useless trivia.

Sorry I don't have the corresponding spring rates.

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Raydar
88 3.4 coupe.

Coming soon...
88 Formula, presently under the knife.

I did some research into '88 spring rates a few years ago. Here's what I found, in two parts.

Before I get into the results, the chart you posted is for front springs only. The rear chart looks like this:

code:

---

Prod #   code  Service #
10053695  PUD  10053695  (stiffest)
10053694  PUC  10053695       |
10053693  PUB  10053693       |
10053692  PUA  10053693  (softest)

---

Part 1:

I did a survey of '88 spring rates. I got 15-20 cars so it was an admittedly small sample, but here's what I found from that:

coupes - about half had ARC front springs, the other half ARD
Formulas - all had ARD front springs
GTs - about half had ARD front springs, the other half FPH

ALL '88s that I surveyed had PUC rear springs.

I told people to list the options of their car when they sent me the spring codes and I was never able to find a correlation. Perhaps it was a combination of things.

Part 2:

I've measured the ARD and PUC springs in two ways. I took them to a race shop a couple years ago and had them checked, and I recently measured them myself using a hydraulic press, a tape measure and a bathroom scale. I posted the results in this thread: https://www.fiero.nl/forum/Forum2/HTML/042357.html

Summary:

PUC: Race shop said 100 lb/in. My setup said 122 lb/in
ARD: Race shop said 175 lb/in. My setup said 171 lb/in

To check for accuracy I also measured a couple Eibach 250 lb/in x 8" x 2.5" springs I had laying around. These both measured 237 lb/in on my setup.

Raydar, your coupe is the first '88 I've ever heard of with PUD springs. Since there was a descrepancy between the RPO label and the tag on the springs I suspect they had been changed. Looking at my above chart (which is from the 22P) you can see that there were four production part numbers but only two replacement part numbers. That means that if you went to the dealer to get a replacement for the PUC spring the replacement part number would be 10053695 which is actually a PUD spring.

Either that or they ran out of PUC springs on the line that day and threw in a pair of PUDs.

Anyway, this has been a bit long winded but I hope it helps.

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Doug Chase
Chase Race
Custom roll cage and exhaust fabrication

Thanks, Doug. A plus for ya! I have been looking at coil-overs for the rear, but do not want to loose the compliance of the stock rate. I've done the over-stiffness routine on previous projects. This time I'm going for optimizing factory settings with U.H.M.W poly and spherical bearings.

Neil

I just dug out an '88 front spring and took some measurements. I thought I'd use those to calculate spring rate and see how that number jived with the other numbers I posted.

Here's the formula, from page 142 of How to Make Your Car Handle, by Fred Puhn:

code:

---

     (W^4)*G
K = ----------
     8*N*(D^3)

---

K is the spring rate in lbs/in
W is the wire diameter in inches
G is a constant, it's 12,000,000 for steel (from the same page of the same book)
N is the number of active coils
D is the diameter of the spring measured at the center of the wire

The measured OD of the spring is 4.384" and the wire diameter is 0.488" so D = 3.896.

Here's where things get interesting. When the spring is free, there are 8.25 active coils. Punching this number into the above formula gets a spring rate of 174 lb/in, very close to what I measured.

When looking at my spring I can see wear marks on the spring where the top and bottom partial coils hit the next coil. If you assume that these coils are touching when the spring is installed that gives us 6.25 active coils. Punching this into the formula gets 230 lb/in which is very close to what T-top Fiero quoted from the MVMA book in the other thread I posted above.

Interesting.

Well, I just happen to have a Formula up in the air right now so I crawled under it and looked. Sure enough, the two end coils of the spring are unused when installed in the car.

I am now changing my official answer to this:

The ARD front spring has a rate of approximately 230 lb/in when installed on the car.

The rear will be more complicated since the spring is somewhat cone shaped. I'll figure out a formula for that and post those results here eventually.

I hope this helps somebody.

Doug

[edit - I bolded my official answer]

[This message has been edited by Doug Chase (edited 12-16-2003).]

It does, thanks again Doug. I'm asking because I'm looking at using progressive rate coils. I think I can get pretty close with these:

http://www.bluecoilspring.com/progressive.htm

But it looks like coilovers only . . .

It gets better...
My coupe's front springs (ARD) were pretty much symmetrical, top to bottom. The end coil on both ends was compressed in. The tip of the coil approaches the wire of the next coil, to within about 3/4", IIRC. (This was until I cut one coil off of one end.)
The Formula front springs that came out of my parts car are very much asymetrical. The coil on one end (the top) almost touches the next coil. The coil on the bottom has the same spacing as the rest of the coils. Sorry I don't have the RPO for these springs. The frame is long gone, and there are no tags on the springs.

Also, I was mistaken about the rear springs on my coupe. The springs were PUD coded, as I remembered. But that is what was called for on the RPO label, too.
FWIW, the car is/was a Duke (obviously) with an automatic, A/C, sunroof, tilt wheel and delay wipers. No other options.

------------------
Raydar
88 3.4 coupe.

Coming soon...
88 Formula, presently under the knife.

[This message has been edited by Raydar (edited 12-15-2003).]

88GT...put me down for ARD/PUC. That is until they are replaced.

I ran the numbers on the PUC rear spring and came up with 163 lb/in. Hmmm. I'm trying to figure out why that one is so far from my measurements (100 lb/in) when the front spring was so close. More to come...

Raydar, that's very interesting! That's the first car I've heard of without PUC rear springs!

Jscott1, thank you. I'll put both of you guys in my database. In fact, maybe it's time to resurrect this project.

By the way, I also discovered that my new Formula has ARC front springs. Another first, I think.

Doug

Doug,

I dont think that the rear spring rate is a constant rate. That is why your calculated number is different then the measured.

Also, due to fatigue, that constant of 12,000,000 is coming down. Even though it is steel, think about how many cycles it has had.

[This message has been edited by Howard_Sacks (edited 12-19-2003).]

Doug: You may be using the wrong constant.

See: http://www.bluecoilspring.com/rate2.htm

According the their information, the constant for steel (Torsional odulus for Steel) is always 11,250,000, not 12,000,000. That difference could throw off the results by about 5%.

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FierOmar