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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; Gents, Hoping to get some feedback on how to get back to some more neutral handling after I overhauled my ...
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    ichpen's Avatar
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    Dump your spring rate and suspension advice here

    Gents,

    Hoping to get some feedback on how to get back to some more neutral handling after I overhauled my suspension.

    Currently running Penske 7500 shocks on 4 corners, Sprint springs (10kg/~570lbs front (10 inch length), 12kg/640lbs rear (10 inch length). Have all other suspension mods inc. beefy swaybars, trailing arms, beefy rear tie rods. Obviously with the S/C up front we have a bit more extra weight to deal with.

    Given that I slapped these on without much thought car's handling has changed quite drastically. From being somewhat neutral to understeer happy, it's now very tail happy. Not necessarily a bad thing for the fun factor but really a nuisance when you're trying to get around a track quicker than the debris collection truck.

    Need to get a bit more neutrality back in, maybe soften up the spring rates also and get the rear under control. Right now car is a bit unsettled (front and rear).

    I'm thinking of breaking the pattern of rear to front spring rate bias and going with 500lbs shorter springs in the rear and 550lbs in front (move up to 12 or longer springs to take up some shock acreage that's going to waste right now).

    Unfortunately can't quite ditch the rear hotchkis sway bar (threw away the factory one) so need to work with it in place.


    I'll get the car properly aligned and corner balanced.

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    tommy compton's Avatar
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    Re: Dump your spring rate and suspension advice here

    I'd trade you my rear Eibach sway for your Hotchkis rear. EIbach has extra holes for ajustability and is just over stock diameter. Have to wait until its a tad warmer out for me to remove it.

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    rand49er's Avatar
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    Re: Dump your spring rate and suspension advice here

    Unfortunately, it's been forty years since I took vehicle dynamics (ME 498) while an undergraduate in engineering, but IIRC it should be able to be corrected by anti-sway bar (torsional) rates and coil spring rates alone (assuming no changes in tires, bushings, ride height, etc.). I know, I know ... I'm not a bit of help.
    '05 CTS-V, Maggie, Kooks, Hotchkis, Ground Control, Corsa, B&M, DSS/Hendrix, Full 3M Clear Bra, Autovation, V Headrests, CTS Console, STS-V 55w Fogs, Black Vette FRCs, Specter Werkes, Katech LS9 Clutch, SS Brake Lines, Heavymetals U-Turn Fuel Line Eliminator, Momo Combat Evo Shift Knob, Wldwhl Clear Sidemarkers, Linea Corse LC855 Wheels or OEM wheels w/'06-'07 Center Caps, plus a couple more. 472 RWHP/411 RWTQ (Mustang Dyno).

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    Re: Dump your spring rate and suspension advice here

    Cheers rand... Send me a book or two to read.

    I'll play around with my adjustable endlinks a bit as I've not checked them out thoroughly. Swaybar is supposed to be neutral with no preload with car down on flat ground, right? Maybe they're preloaded as I've not adjusted them since I started this whole ride height circus.

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    Re: Dump your spring rate and suspension advice here

    Quote Originally Posted by ichpen View Post
    ... Swaybar is supposed to be neutral with no preload with car down on flat ground, right? ...
    Anti-sway bar and preload are mutually exclusive on flat ground. Only during body roll does one side pull down while the opposite pushes up to resist body roll.

    Am I right to think that while turning, you want the rear axle to move in a manner that effectively steers the rear toward the outside of the turn thereby causing the car to rotate about it's CG better thereby (again) lessening understeer (i.e. going toward neutral steer). Too much would obviously cause oversteer, a condition that can work better than caffeine to wake you up at anything approaching triple digits (metric OR Imperial units).
    '05 CTS-V, Maggie, Kooks, Hotchkis, Ground Control, Corsa, B&M, DSS/Hendrix, Full 3M Clear Bra, Autovation, V Headrests, CTS Console, STS-V 55w Fogs, Black Vette FRCs, Specter Werkes, Katech LS9 Clutch, SS Brake Lines, Heavymetals U-Turn Fuel Line Eliminator, Momo Combat Evo Shift Knob, Wldwhl Clear Sidemarkers, Linea Corse LC855 Wheels or OEM wheels w/'06-'07 Center Caps, plus a couple more. 472 RWHP/411 RWTQ (Mustang Dyno).

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    Re: Dump your spring rate and suspension advice here

    I am not an expert on the subject but what I gather from things I've read you're on the right track with reducing the rear spring rates. I always thought the rears were purposely lower than the fronts in most set ups. That along with adjusting the rebound on the dampers and playing with tire pressure might also be helpful. I heard some internet chatter (take it for what it's worth) that you should try to get away with the lowest spring rates in the rear you can. Maybe finding out what the actual wheel rates are from front to rear may help as well. Not sure how to do that, but it is a better correlation of the front in relation to the rear than spring rates. Heres an interesting article from GRMS on tire lateral load transfer distribution and wheel rates. The front seems to be a higher percentage than the rears in most cases. 50/50 is a loose set up. Just remember that spring rates can act like a sway bar. It does cover over and under-steer. The last two paragraphs kind of sum it up. Good luck, I'm sure you'll sort it out.

    http://grassrootsmotorsports.com/articles/lean-less/

    PS zzila's thread says he started with 750 in front and 450 in back. That's in sharp contrast to your set up.

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    Re: Dump your spring rate and suspension advice here

    Quote Originally Posted by crankedupforit View Post
    PS zzila's thread says he started with 750 in front and 450 in back. That's in sharp contrast to your set up.
    For what it may be worth - I just ordered a set of Penke 7500s from Anze. I will be running at stock ride height and the set up is more street than track. The spring rates are to be 700 front and 400 rear. I questioned the rear srping rate, because without the nivomat effect the spring alone will need to accommodate the occasional passenger or luggage weight. Anze's answer was that the coilover 400 lb was closer to a 500 lb spring in the stock location.

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    Re: Dump your spring rate and suspension advice here

    Quote Originally Posted by darkman View Post
    For what it may be worth - I just ordered a set of Penke 7500s from Anze. I will be running at stock ride height and the set up is more street than track. The spring rates are to be 700 front and 400 rear. I questioned the rear srping rate, because without the nivomat effect the spring alone will need to accommodate the occasional passenger or luggage weight. Anze's answer was that the coilover 400 lb was closer to a 500 lb spring in the stock location.
    Makes sense since the further inboard the spring is located the more leverage the wheel has on it. The coil over spring being furthur outboard can have a lower spring rate and still have the same wheel rate.

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    Re: Dump your spring rate and suspension advice here

    Quote Originally Posted by rand49er View Post
    Anti-sway bar and preload are mutually exclusive on flat ground. Only during body roll does one side pull down while the opposite pushes up to resist body roll.

    Am I right to think that while turning, you want the rear axle to move in a manner that effectively steers the rear toward the outside of the turn thereby causing the car to rotate about it's CG better thereby (again) lessening understeer (i.e. going toward neutral steer). Too much would obviously cause oversteer, a condition that can work better than caffeine to wake you up at anything approaching triple digits (metric OR Imperial units).
    Yep, that's what I figured. Will check that the sways aren't loaded. Thanks.


    Quote Originally Posted by crankedupforit View Post
    I am not an expert on the subject but what I gather from things I've read you're on the right track with reducing the rear spring rates. I always thought the rears were purposely lower than the fronts in most set ups. That along with adjusting the rebound on the dampers and playing with tire pressure might also be helpful. I heard some internet chatter (take it for what it's worth) that you should try to get away with the lowest spring rates in the rear you can. Maybe finding out what the actual wheel rates are from front to rear may help as well. Not sure how to do that, but it is a better correlation of the front in relation to the rear than spring rates. Heres an interesting article from GRMS on tire lateral load transfer distribution and wheel rates. The front seems to be a higher percentage than the rears in most cases. 50/50 is a loose set up. Just remember that spring rates can act like a sway bar. It does cover over and under-steer. The last two paragraphs kind of sum it up. Good luck, I'm sure you'll sort it out.

    http://grassrootsmotorsports.com/articles/lean-less/

    PS zzila's thread says he started with 750 in front and 450 in back. That's in sharp contrast to your set up.
    Good article and a sharp sharp contract in rates back to front from what everyone is running. I'll get a 500 spring out back, maybe an inch shorter (give a bit more flexibility to drop the rear a little more). Probably stay with my current spring or go down to 600 out front. Just guessing here.

    Quote Originally Posted by darkman View Post
    For what it may be worth - I just ordered a set of Penke 7500s from Anze. I will be running at stock ride height and the set up is more street than track. The spring rates are to be 700 front and 400 rear. I questioned the rear srping rate, because without the nivomat effect the spring alone will need to accommodate the occasional passenger or luggage weight. Anze's answer was that the coilover 400 lb was closer to a 500 lb spring in the stock location.
    Quote Originally Posted by crankedupforit View Post
    Makes sense since the further inboard the spring is located the more leverage the wheel has on it. The coil over spring being furthur outboard can have a lower spring rate and still have the same wheel rate.
    Interesting, maybe they're onto something.

    Need to get myself some quality springs, hyperco ok?

  11. #10
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    Re: Dump your spring rate and suspension advice here

    Where are your springs in the rear? Are you running the rear coil-over setup that zzilla had ANZE put together, so the rear springs are on the rear dampers? Or are your rear springs in the stock location, like my KWs and (I think) like the Ground Control setups? As crankedupforit and darkman already mentioned, the difference in spring locations will make a significant difference in the rates you should be running. If you're running coil-overs in the rear then it's no surprise that the 12kg/mm springs are making it tail-happy - that's a lot of rear rate!

    FWIW, 12kg/mm is actually ~670#/in, and 10kg/mm is about 560#/in. In other words, your front/rear stagger is even bigger than your post indicates.

    I'm running the "stock" KW V3 springs up front (10kg/mm) and 10kg/mm springs in the rear (stock location with adapters to fit the 60mm springs). The "stock" KW rear springs were 9kg/mm, but I figured that GM chose to put matched front/rear springs (400#/in) on the car, so I would do the same. I'm running a stock front swaybar and a Hotchkis rear swaybar, which feels quite a bit more nimble than having both the front and rear Hotchkis swaybars installed. The car is (IMO) still prone to understeer in slower corners, but not horribly so.

    My understanding is that pretty much all of the coil-over springs are good to go. SSS seems to be the only exception - I've read more that people have more issues with spring sag, rates not matching from one spring to the next, etc. Hyperco, Sprint, H&R, Eibach all are very good quality.
    '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...

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    Re: Dump your spring rate and suspension advice here

    "Need to get myself some quality springs, hyperco ok?"


    They are a top tier manufacture.

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    Re: Dump your spring rate and suspension advice here

    Quote Originally Posted by ichpen View Post
    Need to get myself some quality springs, hyperco ok?
    My coilover setup from Anze comes with Hypercos.

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    Re: Dump your spring rate and suspension advice here

    Quote Originally Posted by AAIIIC View Post
    Where are your springs in the rear? Are you running the rear coil-over setup that zzilla had ANZE put together, so the rear springs are on the rear dampers? Or are your rear springs in the stock location, like my KWs and (I think) like the Ground Control setups? As crankedupforit and darkman already mentioned, the difference in spring locations will make a significant difference in the rates you should be running. If you're running coil-overs in the rear then it's no surprise that the 12kg/mm springs are making it tail-happy - that's a lot of rear rate!

    FWIW, 12kg/mm is actually ~670#/in, and 10kg/mm is about 560#/in. In other words, your front/rear stagger is even bigger than your post indicates.

    I'm running the "stock" KW V3 springs up front (10kg/mm) and 10kg/mm springs in the rear (stock location with adapters to fit the 60mm springs). The "stock" KW rear springs were 9kg/mm, but I figured that GM chose to put matched front/rear springs (400#/in) on the car, so I would do the same. I'm running a stock front swaybar and a Hotchkis rear swaybar, which feels quite a bit more nimble than having both the front and rear Hotchkis swaybars installed. The car is (IMO) still prone to understeer in slower corners, but not horribly so.

    My understanding is that pretty much all of the coil-over springs are good to go. SSS seems to be the only exception - I've read more that people have more issues with spring sag, rates not matching from one spring to the next, etc. Hyperco, Sprint, H&R, Eibach all are very good quality.
    My rear shocks/springs are not coilovers (I've not done the conversion yet) so everything is in stock locations. The only addition is the ground control perch at the rear.

    The only other observation is that the front 10inch long spring I was running seems a tad short installed on the Penske's (given it's a full proper coilover so spring is fully contained within shock) so I'm thinking of sticking with the same rate but getting something longer. I don't think the shock is bottoming out (though I get a nice clunk on heavy comp/rebound, still unsure where that's coming from).

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    Re: Dump your spring rate and suspension advice here

    Quote Originally Posted by ichpen View Post
    Gents,

    Hoping to get some feedback on how to get back to some more neutral handling after I overhauled my suspension.

    Currently running Penske 7500 shocks on 4 corners, Sprint springs (10kg/~570lbs front (10 inch length), 12kg/640lbs rear (10 inch length). Have all other suspension mods inc. beefy swaybars, trailing arms, beefy rear tie rods. Obviously with the S/C up front we have a bit more extra weight to deal with.

    Given that I slapped these on without much thought car's handling has changed quite drastically. From being somewhat neutral to understeer happy, it's now very tail happy. Not necessarily a bad thing for the fun factor but really a nuisance when you're trying to get around a track quicker than the debris collection truck.

    Need to get a bit more neutrality back in, maybe soften up the spring rates also and get the rear under control. Right now car is a bit unsettled (front and rear).

    I'm thinking of breaking the pattern of rear to front spring rate bias and going with 500lbs shorter springs in the rear and 550lbs in front (move up to 12 or longer springs to take up some shock acreage that's going to waste right now).

    Unfortunately can't quite ditch the rear hotchkis sway bar (threw away the factory one) so need to work with it in place.


    I'll get the car properly aligned and corner balanced.
    Are the 7500's non adjust /single adjust/ double adjust? as far as spring rates the rear are going to be lower due to most of the weight of these cars are in the front 60% front 40% rear(these numbers are from Cross weighting the car before any improvments ie stock) ." Hyperco "springs are excellent springs and are run on many different race series. I dont' know where you bought the shocks from if they were from "ANZE ENGINERING" he can and will help with any type of set up you need. Or you can purchase the Hyperco springs from him and he will still help you set your car up. Angelo at Anze have set up many cts v race cars and knows how to get it right( 516) 671-3960 as far as my set up 750 front 450 rear spring rate is perfect so far, but I have not had the chance to use them much due to the fact the car is in the fabrication shop for a widebody kit. So when I get to the track things might change(weight /wing/etc..)

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    Re: Dump your spring rate and suspension advice here

    Thanks sir. I'll give them a call. Out of interest, how long are your front springs (length wise).

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