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2004-2007 Cadillac CTS-V Performance Mods Discussion, Dump your spring rate and suspension advice here in Cadillac CTS-V Series Forum - 2004 - 2007; Originally Posted by cadillactechnician Best advice is to change one thing at a time. If your tire pressures are correct, ...
  1. #31
    tweeter81's Avatar
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    Re: Dump your spring rate and suspension advice here

    Quote Originally Posted by cadillactechnician View Post
    Best advice is to change one thing at a time.
    If your tire pressures are correct, you have no preload in the rear sway bar and you are aligned correctly then reducing rear roll stiffness will in theory reduce oversteer.
    You can reduce your rear roll stiffness by doing a few things. Changing the effective lever arm on the sway bar will change the torsional stiffness of the sway bar. Changing your spring rates with the current spring location will all so change the roll stiffness. If you change both spring location AND spring rate, talk to someone who has done it so you know where to start or then you will start changing more than one thing.

    If you do get an adjustable sway bar then this is the quickest and easiest way to tune the car while at the track.

    Read all of Carroll Smith's books, Prepare, Tune, Engineer and Drive to Win. Chassis Engineering by Herb Adams is a great one too.
    Great info, thanks a bunch! I need to pick up those books for some light reading

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    Re: Dump your spring rate and suspension advice here

    For whatever reason, 9" is some sort of bastard length. I've never understood why, but everyone makes 6, 7, 8, 10, 12, etc, but not 9". Interesting that Swift makes 9" in their metric (65mm) springs, but not in their 2.5" springs. I would just wrap some electrical tape or something like that around the lip of the spring perches to fill in the slight gap when using the 65mm springs with 2.5" perches.
    '05 Stealth Grey CTS-V, Hyper Silver Linea Corse Venetos w/Continental ExtremeContact DWs (summer), black Team Dynamics ProRace 1.2 wheels with 275/35-18 R-compounds (track), Hyperblack Rota Torques (winter), KW Variant3s, V2 front brakes, Hotchkis rear sway bar, EPS cam, TEA-ported 243 heads, FAST92 intake w/LS2 TB, JBA Camaro/G8 1-3/4" shorty headers w/JBA cat pipes, Corsa exhaust, UUC motor and tranny mounts, UUC shifter, MAPerformance trailing arms, Specter cradle bushings, etc...

  3. #33
    FuzzyLogic is offline Cadillac Owners Connoisseur
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    Re: Dump your spring rate and suspension advice here

    I've been reading through this thread, pondering spring rates, and wondered where you guys wound up with your Penske and KW Variant 3 setups. Are you still rocking your present handling balance, and if not, what kind of experimentation have you done in the meantime?

    I had a very similar setup to Tweeter (Ground Control with 650F/750R), which I might have been using to compensate for the poor compression and rebound dampening of the FG2s. As they say, the best thing to do when your suspension sucks it to prevent it from doing anything.

    Now that I have KW Variant 3's, I'm debating the following spring combinations, based on the Swift catalog:

    Option 1 (Soft 46/54 ratio)
    - 2x Stock KW V3 front springs (8" length, 70mm ID, 100 N-m / 574 in-lbs)
    - 2x Z60-228-120 rear springs (9" length, 60mm ID, 120 N-m / 672 in-lbs)

    Option 2 (Medium 50/50 ratio)
    - 2x Z70-203-120 front springs (8" length, 70mm ID, 120 N-m / 672 in-lbs)
    - 2x Z60-228-120 rear springs (9" length, 60mm ID, 120 N-m / 672 in-lbs)

    Option 3 (Stiff 46/54 ratio)
    - 2x Z70-203-120 front springs (8" length, 70mm ID, 120 N-m / 672 in-lbs)
    - 2x Z60-228-140 rear springs (9" length, 60mm ID, 140 N-m / 784 in-lbs)

    I'm lowered pretty far, so the only two things that I'm truly certain of right now are a) I need more rate in the rear to prevent my 285s from rubbing on hard, sustained corners, and b) I want less understeer (which I may be able to derive by tuning the shocks). Presently, my KW Variant 3's are set to stock settings, which is:

    Front Axle
    - 0.75 turns from full hard for compression
    - 0.75 turns from full hard for rebound

    Rear Axle
    - 1.0 turns from full hard for compression
    - 1.0 turns from full hard for rebound

    Another important question is, has anyone with a KW Variant 3 found out how much spring is too much for the KW Variant 3's rebound dampener valving?

  4. #34
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    Re: Dump your spring rate and suspension advice here

    Quote Originally Posted by FuzzyLogic View Post
    Another important question is, has anyone with a KW Variant 3 found out how much spring is too much for the KW Variant 3's rebound dampener valving?
    I was told by KW that about 200 lbs is the max increase in rate that the stock valving can handle. They also told me that the warranty is voided if you change the stock spring rate on the KW V3s. Not sure how they would know that you changed them. The issue then becomes figuring out some new settings to start with. With this they have not been too authoritative with the response. I suppose you can quantify the increase of the spring rate as a percentage and then apply that to the stock settings but that's yet to be proved out. I'm debating as to whether I can make the V3s more track worthy or would just going to Penskes be the solution.
    FuzzyLogic and FuzzyLogic like this.
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    Re: Dump your spring rate and suspension advice here

    Quote Originally Posted by crankedupforit View Post
    I was told by KW that about 200 lbs is the max increase in rate that the stock valving can handle. They also told me that the warranty is voided if you change the stock spring rate on the KW V3s. Not sure how they would know that you changed them. The issue then becomes figuring out some new settings to start with. With this they have not been too authoritative with the response. I suppose you can quantify the increase of the spring rate as a percentage and then apply that to the stock settings but that's yet to be proved out. I'm debating as to whether I can make the V3s more track worthy or would just going to Penskes be the solution.
    Great info. Frankly, the stock springs and damper settings on the KW Variant 3's are super comfortable compared to my Ground Control setup. But the Ground Control setup felt much snappier when pushing the car hard.

    By the way, do we have a live axle, and if not, what on Earth is that thing in the back? Most of the calculators that I've seen are only good for A-arm setups. The Eibach calculator includes the equations for a live axle, which seems closer to what we have, but not quite correct.

    Ultimately, I plan on putting together an Excel spreadsheet, with measurements for everyone to see (including sprung and unsprung weights, as best as I can get). Maybe even something like the Excel Web App this guy did (see the right sidebar).

  6. #36
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    Re: Dump your spring rate and suspension advice here

    I'm still running on the same setup I've had for years now and really like it. My heavy springs seem to play well with the FG2s, but I don't put a ton of miles on the car either and I've only had this setup for about 7000 miles.

    Btw, I've said this before in other threads, but I have more rubbing on hard turns in the rear with my 285/35r19s (currently installed) than I had with the 295/30r19s. That extra sidewall kills you.

  7. #37
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    I miss my GC 650/700 w/ T2 shocks...


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  8. #38
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    Re: Dump your spring rate and suspension advice here

    Quote Originally Posted by thebigjimsho View Post
    I miss my GC 650/700 w/ T2 shocks...
    That is literally the perfect setup for the first gen V as far as suspension goes.

  9. #39
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    Re: Dump your spring rate and suspension advice here

    Quote Originally Posted by thebigjimsho View Post
    I miss my GC 650/700 w/ T2 shocks...

    Did you ever get that to work right? I thought you were always working something out on that setup?

  10. #40
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    Re: Dump your spring rate and suspension advice here

    Quote Originally Posted by FuzzyLogic View Post
    By the way, do we have a live axle, and if not, what on Earth is that thing in the back?
    Live axle = solid axle (think Mustang and pickup trucks and old muscle cars). No, we don't have a live axle. The rear is a multi-link IRS.
    '05 Stealth Grey CTS-V, Hyper Silver Linea Corse Venetos w/Continental ExtremeContact DWs (summer), black Team Dynamics ProRace 1.2 wheels with 275/35-18 R-compounds (track), Hyperblack Rota Torques (winter), KW Variant3s, V2 front brakes, Hotchkis rear sway bar, EPS cam, TEA-ported 243 heads, FAST92 intake w/LS2 TB, JBA Camaro/G8 1-3/4" shorty headers w/JBA cat pipes, Corsa exhaust, UUC motor and tranny mounts, UUC shifter, MAPerformance trailing arms, Specter cradle bushings, etc...

  11. #41
    OneFast V is offline Cadillac Owners Enthusiast
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    Re: Dump your spring rate and suspension advice here

    Quote Originally Posted by FuzzyLogic View Post
    Great info. Frankly, the stock springs and damper settings on the KW Variant 3's are super comfortable compared to my Ground Control setup. But the Ground Control setup felt much snappier when pushing the car hard.

    By the way, do we have a live axle, and if not, what on Earth is that thing in the back? Most of the calculators that I've seen are only good for A-arm setups. The Eibach calculator includes the equations for a live axle, which seems closer to what we have, but not quite correct.

    Ultimately, I plan on putting together an Excel spreadsheet, with measurements for everyone to see (including sprung and unsprung weights, as best as I can get). Maybe even something like the Excel Web App this guy did (see the right sidebar).
    This is the best excel spring rate calculator i have found to date. http://www.pirate4x4.com/tech/billav...tor%20V6.4.xls

  12. #42
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    Quote Originally Posted by odla View Post

    Did you ever get that to work right? I thought you were always working something out on that setup?
    No, once I got out of the QA1s and got the T2s in(thanks Pat!), it was V nirvana...

    And while it was an increase in firmness of a greater jump from the FG2 than the FG2 was from FE4, it was never harsh. I only had them in for a week, but I had many miles on a trip from Boston to Chicago and was coming back and in WV when I had the deer incident that ended the '04...


    -- We miss you, JD (Dirt_Cheap_Fleetwood)


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    Re: Dump your spring rate and suspension advice here

    sucks you only got so little time with them on. I would liked to have heard your opinion on them on the track. What were the cost of the t2's?

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    Pat(AAIIIC) practically gave them to me. Actually, I don't remember, but they were cheap.


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