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  • S Series Aftermarket Spring Rates

    Spring Rates:
    OEM Springs: ............................ 126 lb/in Front, 129 lb/in Rear
    H&R Race (1.4"F, 1.3"R):.............. 310 lb/in Front, 250 lb/in Rear
    H&R Sport (1.4"F, 1.3"R):............. 205 lb/in Front, 195 lb/in Rear
    Eibach Pro Kit (1.3"F, 1.1"R):........ 149 lb/in Front, 91-159 lb/in Rear
    Progress Group (1.8"):................. 200 lb/in Front, 170 lb/in Rear
    Progress Group (1.3"):................. 156 lb/in Front, 150 lb/in Rear
    Sprint (2.0"):............................. 200 lb/in Front, 140 lb/in Rear
    Sprint Extreme(2.5"): .................. 200 lb/in Front, 140 lb/in Rear
    Suspension Techniques (1.4"):...... 157 lb/in Front, 109-155 lb/in Rear

    KYB GR-2 front: 30% stiffer than stock
    KYB GR-2 rear: same as stock
    ST front:*
    ST rear:*

    *No one knows any real specifics on the ST struts as far as dampening goes. But the general consensus is that they are stiffer than KYB GR-2s.
    Comments 2 Comments
    1. 85HP's Avatar
      85HP -
      Some of the stock springs have slightly higher rates than what is generally accepted, and there are a few different ones to choose from.

      All have a tangential end and a pigtail end -- I mention this because 'tangential' end springs can indeed be cut, resulting in both lowering and a (counterintuitive) increase in spring rate... which might be useful.

      I ordered some of the Rockwell '681s on closeout, and the tangential end sure looks like a 'square' end to me (the last 1/2 turn on the helix on that end is bent back a little -- hard to describe, but it's not uniform with the neighboring turns) Bottom line: I'm not sure these can be cut.

      BTW, regarding cutting springs: is a good starting place. There are many spring calculators online.

      The following data is from with my added comments. The Moog part numbers mostly cross to Rockwell, substitute RV- as a prefix, e.g. RV662. Other aftermarket manufacturers of 'stock' replacement parts seem to be out of the game at this point, but the part numbers are similar.

      Some of these are variable rate, and I have no idea what the actual numbers are versus deflection. I have a friend (ME prof) at a local university... will see if I can get some time on his Instron machines for testing.

      These data are confirmed with cross references from Rock Auto,, and other sites. Hopefully I typed it all in right. The first two are fronts, the rest are rears.

      mfg-p/n i.d. (in) bar dia. (in) loaded height (in) load (lbs) spring rate (lb/in) free height (in) comments
      MOOG-CC662 4.900 .531 10.00 374 143 12.72 88913661 ACDELCO 45H1128 (auto trans, Front, w/o AC) All SCx 91-02, all SLx 91-02, SW1 93-99, SW2 93-01, cross to 88913661
      MOOG-CC664 4.900 .531 10.00 421 143 13.06 88913662 ACDELCO 45H1129 (std trans, Front, w/AC) same application as 662 Variable Rate, cross to 88913662, 21012016
      MOOG-CC673 4.133 .515 11.00 339 132 13.63 21011642 first gen coupe and sedan, rear
      MOOG-CC677 4.133 .515 11.00 382 132 13.89 Variable Rate 93-95 SW, 91-02 SL and SL1, 96-02 SL2
      MOOG-CC679 4.133 .531 11.00 426 147 13.88 rear, variable rate, 93-99 SW1
      MOOG-CC681 4.133 .531 11.00 517 147 14.47 21012616 96-01 SW2
    1. siris's Avatar
      siris -
      I noticed years ago that there were variable spring rates available for these turds, but assumed it was just aftermarket jibberish because of the commonly accepted 128lb/in spring rate.
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