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Moog Spring Rates
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Moog Spring Rates

Front Coil Springs

Front Springs
Inside
Diameter
Moog
Number
Wire
Diameter
Load
Height
Spring Rate
lb./in
Free
Height
OEM
Applic.
Spring force @ installed height Force at wheel Front end weight
4.080 5598 0.672 11.000 346 15.387 G-body 1517 1062 2124
4.085 5600 0.672 11.000 346 15.616 G-body 1597 1118 2236
4.085 5602 0.672 11.000 346 15.847 G-body 1677 1174 2348
4.085 5604 0.672 11.000 346 16.076 G-body 1753 1227 2454
4.085 * 5606 0.690 11.000 420 14.637 G-body 1530 1071 2142
4.085 * 5608 0.690 11.000 420 14.897 G-body 1637 1145 2290
4.085 5610 0.690 11.000 420 15.157 G-body 1745 1222 2444

4.085 5658 0.690 10.750 579 13.176 S-series 1405 984 1968
4.085 5660 0.720 10.750 639 13.159 S-series 1539 1077 2154
4.085 5662 0.740 10.750 706 13.149 F-body 1693 1185 2370
4.085 ** 5664 0.760 10.750 767 13.184 F-body 1870 1309 2618
The primary springs used in G-bodies were also used in most F-bodies. There were a few others not listed that shared the same rates.
Not sure where they get the load height value, I had to compress the spring to 11" to get it in the arm! Probably 8 or 9".

By Rob Smith

Appended by Jeff Davidson with permission.

As you can see by the added numbers, there are numerous springs of the same spring rate available. This allows the spring to be matched to the weight of the vehicle since, depending on options, the ride height would vary if only one spring was available. If you know the weight of the front axle of your car, you could pick a spring that would give you the ride height you desire.

Example:

Let's say you want to use the 5658 S-10 spring in your Monte to gain some spring rate. Assume you already have 5606 springs in your Monte. Let's install a set of 5658 and see what happens. We know that we already have a front end weight of 2142 pounds (assumed) or, 1530 pounds at the spring, but if you look at the installed height weight capability of the 5658, you can see that it can't support that weight, at that height, so it compresses until it can. In this case, it compresses about .5" further than the 5660 does for the same weight vehicle.

The following chart shows the various spring forces generated by the different springs. As you can see, the stiffer springs lose much of their "push" at heights greater than their Installed Height. The 5606 produces almost twice the force at a 12.00" loaded length than the 5658 does. This should help handling as there will be less weight transferred when cornering. The stiffer spring will decrease body roll as well. One interesting comparison is the 5606 and the 5658. These two springs would have similar ride and produce the same force at around 9.00" height, but the 5658 force drops off rapidly under rebound conditions when the spring height gets above 10.75". This should prevent the vehicle from rising too far in the front in response to a rise in the road and get rid of the "floaty" feeling of excessive rebound. But, the 5660 will provide more spring rate if the spring is going to be shortened to attain a custom ride height. You already get around a .25" drop, but that really depends on the actual weight of the vehicle involved. If you want an even stiffer ride, the 5662 springs have been used with good success by several members of the Monte Carlo Mailing list. This spring will really resist the tendency to bottom the front suspension and is needed if you choose to lower the front end by two inches. If you only want to lower by one inch, trimming a quarter or half coil off of the 5660 would probably sufficient to give the ride height you desire and not bottom. The 5662 is strong enough to resist almost .75" of further travel compared to the 5658 and about .5" compared to the 5660.

Stare at this chart for a while and you will see how different springs function. Interesting!

Spring Comparator-Various forces from various springs and ride heights

Original application

SS spec SS spec S-10 S-10 F body
Part Number 5606 5608 5658 5660 5662
Spring Rate 420 420 579 639 706
Load Height 11.00 11.00 10.75 10.75 10.75
Free Height 14.637 14.897 13.176 13.159 13.149
lbs @ load height 1528 1637 1405 1539 1694
Compressed height
12.00 1108 1217 681 741 811
11.75 1213 1322 826 900 988
11.50 1318 1427 970 1060 1164
11.25 1423 1532 1115 1220 1341
11.00 1528 1637 1260 1380 1517
10.75 1633 1742 1405 1539 1694
10.50 1738 1847 1549 1699 1870
10.25 1843 1952 1694 1859 2047
10.00 1948 2057 1839 2019 2223
9.75 2053 2162 1984 2178 2400
9.50 2158 2267 2128 2338 2576
9.25 2263 2372 2273 2498 2753
9.00 2368 2477 2418 2658 2929

Blue highlighted ( and bold) fields indicate design installed height. Notice that the 5658 would drop the front end almost an inch compared to the 5606. Cells with red borders indicate the installed height relative to the 5606 (around 1500 lbs spring force). Yellow highlights indicate spring force closest to 2400 pounds.

So, you can see that swapping in a 5658 spring in place of the 5606 would drop your front end about a half inch, if nothing else is changed! If you wanted a little more drop, then the spring could be trimmed, but only a little, instead of putting in a spring with way off dimensions and having to cut off a lot of coil. Since the design installed height of the 5606 is 11" and the installed height of the 5658 is 10.75", you would get an immediate .25" drop IF the 5658 could carry the same weight at that height, but we have seen that it doesn't, so it compresses until it can. The 5662 springs would give a normal ride height compared to the 5606 springs. If you trim coils off, you can re-measure the Free Height, but, the spring rate goes up a little when you shorten the spring.

The math:

To get the compression force on the spring at the installed height (meaning-car sitting on its wheels), take the Free Height and subtract the Load Height from the above charts. Then multiply that result by the spring rate for that particular spring. I assumed a relative wheel rate by multiplying the spring force by .7 to simulate the lower control arm. I based it on some simple measurements of the lower control arm, but .7 is close enough for our purposes. You can then multiply the last number (force at the ball joint) times 2 to see what the front end weight is. If you know the weight of the front end, you can work backwards through the math.

Free Height minus Load height equals distance spring is compressed when installed and holding up vehicle.

This distance times the spring rate equals the amount of force the spring is exerting on the suspension at the point where the spring contacts the lower control arm.

Rear Coil Springs

Rear Springs
Inside
Diam.
Moog
Number
Wire
Diam.
Load
Height
Spring Rate
lb./in
Free
Height
OEM
Application
Pigtail
Type
Spring force @ installed height
5.580 5379 0.552 10.25 121 14.750 G-body 19 545
5.580 6321 0.531 10.25 118 14.300 G-body 19 478
5.570 5391 0.590 10.25 142 15.400 G-body 19 731
4.300 5665 0.484 10.25 107 15.420 F-body 17 553
4.310 6377 0.504 10.25 141 13.690 Monza / Sunbird 17 485
5.530 5413 0.580 8.50 167 12.930 A-body 19 738
5.580 5409 0.552 7.50 143 13.440 A-body 19 849
4.300 5659 0.500 10.00 162 13.550 ? 17 575
4.300 5661 0.500 10.00 162 14.000 ? 17 648

Note: The style 19 is double pig tail and style 17 is single pigtail, open coil top.

The following chart shows the spring included in the chart above, but with spring forces at various heights added. It's interesting to note that at least four of these springs would supply the stock ride height for a Monte SS, even though some were not intended for that application. The rear springs seem to have more variances than the front springs. It looks like at least two of them are intended for station wagon use (5391, 5461). The 6377 spring for the Monza would lower a Monte about a half inch and has the open coil style at the top so it could be trimmed slightly to lower the rear further.

Spring Comparator-Various forces from various springs and ride heights
Application G body G body G body F body Monza A body A body

?

Part Number

5379

6321

5391

5665

6377

5413

5409

5659

Spring Rate 121 118 142 113 141 166 140 162
Load Height 10.25 10.25 10.25 10.25 10.25 8.50 7.50 10.00
Free Height 14.768 14.300 15.362 15.214 13.895 12.944 13.539 13.550
lbs @ load height 545 478 731 553 485 738 849 575
Compressed height
12.00 333 271 483 366 238 155 206 251
11.75 363 301 518 393 274 197 242 292
11.50 393 330 554 419 309 239 277 332
11.25 424 360 589 446 344 281 313 373
11.00 454 389 625 473 379 322 349 413
10.75 484 419 660 500 415 364 385 454
10.50 514 448 696 526 450 406 420 494
10.25 545 478 731 553 485 448 456 535
10.00 575 507 767 580 520 489 492 575
9.75 605 537 802 607 556 531 528 616
9.50 635 566 838 633 591 573 563 656
9.25 666 596 873 660 626 615 599 697
9.00 696 625 909 687 661 656 635 737

The aqua color represents the design installed height. Note that the two F-body springs are designed for a 10.25 installed height, so they don't appear on the chart. The red outlined squares indicate the height that spring would sit at at the same load as the 5379 spring.

After doing some investigation, I have determined that a load height of 10.25 for the rear springs is more realistic. One list member said that is where the stock Monte SS should sit. The spring loads match better using 10.25 as a reference, also.


ATGO is not responsible for any damage done to your vehicle by following the above instructions.


 
 

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