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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; I keep saying Sprint. They're actually Swift metric coilover springs......
  1. #16
    ichpen's Avatar
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    Re: Dump your spring rate and suspension advice here

    I keep saying Sprint. They're actually Swift metric coilover springs...

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    Rollbar is offline Cadillac Owners Member
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    Re: Dump your spring rate and suspension advice here

    I'm also on Penskes with stock locations and use 750# front and 550# rear.This combo is ugly on street but great on track.I don't know spring length but think I'm 1 inch lower than stock.IMHO your rear is too stiff and too tall.I'm no expert but I tried lowering the front only by 3/4 inch last time at track and car gained oversteer.After 1 session I changed back and once again became fairly neutral.Again,I'm no expert at set-up but think relative height from front to rear is pretty important.

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    Re: Dump your spring rate and suspension advice here

    Thanks for the feedback. Sounds pretty aggressive. I'm guessing you're still running shock next to spring config in the rear. I was thinking of going an inch shorter on the rears and use that GC perch for street.

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    Re: Dump your spring rate and suspension advice here

    Quote Originally Posted by odla View Post
    "Need to get myself some quality springs, hyperco ok?"


    They are a top tier manufacture.
    Quote Originally Posted by darkman View Post
    My coilover setup from Anze comes with Hypercos.

  5. #20
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    Re: Dump your spring rate and suspension advice here

    I, too, am in need of some advice from you suspension gurus.

    I'm currently running the GC Kit (lowered about 1" front and 1/2" rear) with 750 lb / 800 lb Eibach springs. I like the setup, I don't have much understeer (or excessive oversteer) at all, and the car feels nice and planted and balanced (neutral).

    I bought ichpen's used QA1s, and plan to swap my current FG2s with them. I really am excited about the adjustability of the QA1s.

    My question is this: I think I am going to need to bite the bullet and order some shorter springs for the rear because for some reason, I can't get the rear down as low as I would like it to be (for the street). I need the extra 1" of drop that shorter rear springs would allow me to have, and I could still raise the ride height up plenty if I needed to.

    I am thinking about keeping the front Eibach 750 lb/in springs, and going with some Swift or Hyperco 14 Kg/mm (784 lb/in), 2.50 in diameter coils, in the 9" length (I'm guessing right now, I think the Eibachs are 10" tall). I have had great luck with running 50 lb/in stiffer springs in the rear compared to the front, but with all this talk about going lower in the rear, I am wondering if I should drop down to a less stiff spring in the rear. I know that the guys changing over to the true rear coilover will need the much softer rear springs because of the mouning location being moved in-board, but how about use guys who still use the stock suspension setup (geometry). Any help would be MUCH appreciated.

  6. #21
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    Re: Dump your spring rate and suspension advice here

    I don't think you can go to a shorter spring on the rear w/ the GC setup. Remember the kid in Sacramento who cut his springs...and they fell out. The 10" springs stay in the perch, with some movement, when the suspension is fully unloaded. Maybe a 9" spring will stay, but I'd be very worried. And I have NO idea how it would affect the V's ride and handling...

  7. #22
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    Re: Dump your spring rate and suspension advice here

    Quote Originally Posted by thebigjimsho View Post
    I don't think you can go to a shorter spring on the rear w/ the GC setup. Remember the kid in Sacramento who cut his springs...and they fell out. The 10" springs stay in the perch, with some movement, when the suspension is fully unloaded. Maybe a 9" spring will stay, but I'd be very worried. And I have NO idea how it would affect the V's ride and handling...
    Yeah, that is definitely a concern, but without completely changing my suspension, I don't really have any other options but using a shorter spring to get the ride height that I am looking for. The funny thing is that when I was running the 650 lb/in springs in the rear, my ride height was closer to where I wanted it because those springs would compress slightly under the cars own weight, but the heavy 800 lb spring don't compress at all. Anyway, I am pretty much ready to drop the $200 on two (2) rear springs and have the shop put them in at the same time as they do the QA1 install, but I guess I am more concerned about the spring rate. If I can make the car handle even better with a different spring rate, then I would like to do that at the same time for no extra expense.

  8. #23
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    Re: Dump your spring rate and suspension advice here

    I'm no expert on the GC setups, but do you have the MightyMouse spacer mod in the rear? My understanding is that without the MM mod the stock rear struts will pump themselves back up to (near) stock ride height. I've never had to deal with that, so my understanding could be incorrect. If my understanding is correct, and if you don't have the MM spacers, then the ride height issue will be resolved by going to the QA-1s, since they aren't Nivomat dampers and thus don't pump themselves up.

    $200 for 2 springs is a bit much. Make sure you check the various circle track racing vendors - HRPworld, Coleman Racing, Pegasus Racing, Racer Parts Wholesale, etc - to get a good price. Should be closer to $150 shipped.

    As for rates, if 750/800 is working for you now, I wouldn't change it. That's just based on the "don't change too many things at once" theory - the more stuff you change, the harder it is to figure out what changes were good and what were bad. I would get the QA-1s installed and play with those a bit, then see if you want/need to change the spring rates. Swapping out the rear springs is really pretty easy if you're keeping the springs in the stock location with adapters.

  9. #24
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    Re: Dump your spring rate and suspension advice here

    Quote Originally Posted by AAIIIC View Post
    I'm no expert on the GC setups, but do you have the MightyMouse spacer mod in the rear? My understanding is that without the MM mod the stock rear struts will pump themselves back up to (near) stock ride height. I've never had to deal with that, so my understanding could be incorrect. If my understanding is correct, and if you don't have the MM spacers, then the ride height issue will be resolved by going to the QA-1s, since they aren't Nivomat dampers and thus don't pump themselves up.

    The GC Kit came with a spacer to fool the FG2 Nivomats from pumping up, so that isn't the issue, but thanks for taking a stab at it anyway.

    $200 for 2 springs is a bit much. Make sure you check the various circle track racing vendors - HRPworld, Coleman Racing, Pegasus Racing, Racer Parts Wholesale, etc - to get a good price. Should be closer to $150 shipped.

    That is what I was thinking too, I would feel a lot better only having to spend $150. It just really sucks that I can't get that extra 3/4"-1" of drop out of the rear with my current setup! So then I spend another $150 for that perfect stance so the car looks good at carshows.

    As for rates, if 750/800 is working for you now, I wouldn't change it. That's just based on the "don't change too many things at once" theory - the more stuff you change, the harder it is to figure out what changes were good and what were bad. I would get the QA-1s installed and play with those a bit, then see if you want/need to change the spring rates. Swapping out the rear springs is really pretty easy if you're keeping the springs in the stock location with adapters.
    Great advice (and TBJS too)! I was leary about wanting to change too much, I just don't like wrenching on the car more than I absolutely have to, so I tend to overdo it when I am having work done on the car anyway. But, I think your advice is sound, I will probably just order (2) 784 lb/in (2.5 dia, 9" length --> can anyone confirm this is the correct measurements I would need?) Swift springs and go from there.

    BTW, what is the best and easiest way to just pull out the rear springs and change them to new ones? I had envisioned trying to do it without even unbolting anything (maybe using a small spring compressor to squish the spring enough to pop it out from under the GC spring perch), but that might not be possible...

  10. #25
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    Re: Dump your spring rate and suspension advice here

    Quote Originally Posted by tweeter81 View Post
    Great advice (and TBJS too)! I was leary about wanting to change too much, I just don't like wrenching on the car more than I absolutely have to, so I tend to overdo it when I am having work done on the car anyway. But, I think your advice is sound, I will probably just order (2) 784 lb/in (2.5 dia, 9" length --> can anyone confirm this is the correct measurements I would need?) Swift springs and go from there.

    BTW, what is the best and easiest way to just pull out the rear springs and change them to new ones? I had envisioned trying to do it without even unbolting anything (maybe using a small spring compressor to squish the spring enough to pop it out from under the GC spring perch), but that might not be possible...
    You will need to unbolt the bottom of the shock. But it's one bolt. Then take a pry bar and push the rear axle downward and you should be able to get in there and wiggle the spring out. I would get the prybar firmly in place and step on it lightly. It takes more time getting the to the upper shock mount than replacing the spring.

    BTW, here you go. Best prices. Fast shipping...

    http://shop.a1racing.com/hyp1810b.aspx

  11. #26
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    Re: Dump your spring rate and suspension advice here

    Interesting, if you want to go with 9", A1 only has a 2.25" ID, not 2.5". Don't know what to say on that one...

  12. #27
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    Re: Dump your spring rate and suspension advice here

    Quote Originally Posted by tweeter81 View Post
    Yeah, that is definitely a concern, but without completely changing my suspension, I don't really have any other options but using a shorter spring to get the ride height that I am looking for. The funny thing is that when I was running the 650 lb/in springs in the rear, my ride height was closer to where I wanted it because those springs would compress slightly under the cars own weight, but the heavy 800 lb spring don't compress at all. Anyway, I am pretty much ready to drop the $200 on two (2) rear springs and have the shop put them in at the same time as they do the QA1 install, but I guess I am more concerned about the spring rate. If I can make the car handle even better with a different spring rate, then I would like to do that at the same time for no extra expense.
    It is true stiffer springs will keep the car from squatting. I had 900lb springs on there for awhile. Personally, I think your springs are stiff enough. The stiffness of the QA1s on their stiffer setting is going to firm up handling plenty whether you run 600lb springs or 900. The rear springs are easy to swap. Get the QA1s in and keep your rear seat out for awhile and play with the springs as you see fit.

    I agree with Pat, try to change things little by little and you'll learn what works better, better...

  13. #28
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    Re: Dump your spring rate and suspension advice here

    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.

  14. #29
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    Re: Dump your spring rate and suspension advice here

    Quote Originally Posted by thebigjimsho View Post
    Interesting, if you want to go with 9", A1 only has a 2.25" ID, not 2.5". Don't know what to say on that one...
    Yeah, that sucks. I looked on Hyperco's website and apparently that is the only size that doesn't come in a 2.5" diameter. They have all different lengths around it, but no dice on the 9"...ridiculous. I guess I'm stuck with one of the other brands.

  15. #30
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    Re: Dump your spring rate and suspension advice here

    Quote Originally Posted by thebigjimsho View Post
    It is true stiffer springs will keep the car from squatting. I had 900lb springs on there for awhile. Personally, I think your springs are stiff enough. The stiffness of the QA1s on their stiffer setting is going to firm up handling plenty whether you run 600lb springs or 900. The rear springs are easy to swap. Get the QA1s in and keep your rear seat out for awhile and play with the springs as you see fit.

    I agree with Pat, try to change things little by little and you'll learn what works better, better...
    It is pretty stiff, that is why I will run the QA1s on the softer setting on the street, for a little bit more compliance. The only reason I went with such stiff springs in the first place is because with the wide tires that I like to run (used to be 285s, then it was the 295 R888s, and now back to 285s again) I get rubbing on high-G corners (in track conditions only). The 800 lb springs basically did away with the rubbing, since the car doesn't really sway or squat at all now. Believe me, if I could run softer springs and not get that rubbing, I definitely would.

    Edit: I placed the order for the Swift 784 lb/in springs. Price was $160 shipped, a little cheaper than normal because a sale was going on...still too expensive for a couple of springs.

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