Cadzilla

iTrader: (3)

Really? What was the issue with it?

I considered it only to possibly suspend the upper mount and get less clunk against the body ...the clunking drives me nuts!...

Skidmarcx

I'm learning something about the GC gear haha... Nice I guess I didn't read enough into the part numbers. Yea I'm not worried about being slammed I just want a more firm and planted ride...

And to add to the conversation I think KSport is garbage I've known people to use their coilovers on imports and had failures, noises, adjuster rings seizing, etc

NeverSatisfied02

iTrader: (12)

I'm learning too. This thread should be a sticky. Lots of good info!

FuzzyLog1c

iTrader: (4)

Prerequisite:

http://performance-suspension.eibach...gratesheet.pdf

The above document implies that you should be trying to preload your springs to 80% of their stock height and avoid compressing them to more than 30% of their stock height.

What I believe Eibach did when they originally came up with this kit was to round the 3850 lb curb weight of the CTS-V to 4,000 lbs and distribute it equally amongst all four springs. With their stock 500 lb, 10" long springs and 1000 lbs applied per spring, that would create the perfect 2" drop or 80% preload.

Since the rear springs are mounted separately from the rear shocks, the springs should experience more force compared to the front springs and therefore compress more during bumps (paraphrasing what one of the GC guys told me on the phone). That's why GC utilized 50 lbs more rear springs.

Unfortunately, I think they made a couple of mistakes. The weight of the CTS-V with 17.5 gallons of gasoline and a 180 lb driver is actually 4130 lbs. And it has a 54/46 weight distribution (2230 lbs front, 1900 lbs rear). Divide those numbers in half and you have 1,115 lbs applied to each front spring and 950 lbs on each rear spring.

Here's where it all comes together:

1. Assuming 1,115 lbs preload per front spring, if you select 650 lb springs, your front springs will compress 1.72" when you set your car on them. That's only 83% preload on a 10" spring, but it's 78.5% preload on an 8" spring.

If you had selected the standard 10", 500 lb springs that come with the kit, you would've been fine, but with the higher spring rate, you won't have the correct preload and as a side effect, the car will ride higher.

Fortunately, here, the GC kit gives you plenty of adjustability, so if you don't care about the finer points discussed above, you can definitely get away with 10" springs (as I have for years).

2. Assuming 950 lbs preload per rear spring, if you select 650 lb springs, your front springs will compress 1.46" when you set your car on them. That's only 85% preload on a 10" spring, but it's 82% preload on an 8" spring.

3. Based on the weight distribution and rear suspension design, I think it could be argued that CTS-Vs should be running equal-sized springs on both front and back wheels. As identified in #2 above, preload is still out of spec when with the 8" springs when you're simply looking at weight. Once the design of the rear suspension compensates, you're closer to an optimal design.

4. You're slightly further away from coil bind with 8" springs than 10" springs. Then again, coil bind might save you from damaging a fender during a big hit, but you have bump stops for that.

10" 650 lb spring - 1.72" preload = 8.28" spring height
30% of 10" is 3"
8.28" - 3" = 5.28"
5.28" @ 650 lbs = 3432 lbs (static load) before coil bind

8" 650 lb spring - 1.72" preload = 6.28" spring height
30% of 8" is 2.4"
8.28" - 2.4" = 5.88"
5.88" @ 650 lbs = 3822 lbs (static load) before coil bind

http://bump-drafts.com/2010/01/12/na...nd-bump-stops/

garrettg

iTrader: (1)

KW V3 set is similar comes with 250mm(~10inch) rear springs 60mm ID 90N/mm or 514 pound/inch so 575/514. After towing bikes a few times the rears were more than slammed so I have decided to order a set of 110 N/mm (628 pound/inch) so 575/628 f/r setup similar to the popular 600/650 GC setup. No worries about rear jacking it self up with KW v3 however that may be helpful when loading up the trunk and towing. These kits are great given the spring rate choices out there for flexibility. I would highly recommend the GC or KW kit over buying the hr sport springs.

CTSV_510

iTrader: (1)

No, that's just wrong. I installed hotchkis sway bars and they had a small noticable effect on body roll. I installed the ground control with 600/650 springs and it reduced body roll by at least 2 times that of the sway bars.

Sway bars help to compress the inside spring of the car when the outside spring is being compressed from weight transfer in a turn. They help compensate for body roll, I agree.

Stiffer springs are more resistant to compression, so when cornering and the weight transfers to the outside springs, stiffer springs do not compress as much and so the car does not lean/roll as much.

Sometimes I think you get so caught up with your research and reading that you forget to think.

Can you explain how springs have nothing to do with body lean?

FuzzyLog1c

iTrader: (4)

Your statement about the GC 600/650 springs reducing body roll more than the Hotchkis sway bars is puzzling. I had exactly the opposite experience, but I ran the modifications the opposite way (springs first, sway bars second).

I feel bad about posting a Wikipedia quote here, but I've got to be at work in 30 minutes:

http://en.wikipedia.org/wiki/Sway_bar

"A sway bar increases the suspension's roll stiffness—its resistance to roll in turns, independent of its spring rate in the vertical direction."

As I understand it, three things resist body lean: your shocks, springs, and sway bars. Shocks are primarily intended to dampen movement. Springs contribute to resisting shock compression, but are primarily intended to return shocks to their nominal position, and sway bars transfer differential load through torsion (which is why thicker bars deflect less and transmit more load) away from the heavily loaded axle.

Personally, all I noticed with the stiffer Eibach springs was a reduced tendency for my CTS-V to squat or nose dive under acceleration and braking. When I lowered the car by 1.5" using the GC kit, body lean was significantly reduced, but that wasn't a function of the springs themselves. It was because of the vehicle's new, lower CoG. When I added a sway bar on top of all of that, the car became very resistant to body lean and made it possible to "comfortably" (relatively speaking) exceed the traction provided by the 245/45-18 KDW 2's on my wheels during continuous cornering.

In summary, kudos to you for reminding me (/facepalm) that springs contribute to resisting the compressive loading of shocks during cornering.

Skidmarcx

Great discussion guys... I like the specific info. Another thing I'd like to ask is how lowering the car affects the swaybar? I understand the angle changes and there are adjustable endlinks, but what is the optimum angle?

On the spring topic I'm wondering if I shouldn't try a 600/600 combo since I have a pretty extensive audio setup putting my car at roughly 4100 without me in it. My weight distribution has to be close to 50/50 now

branland

iTrader: (2)

How are you measuring your preload? Are you loading the spring in the perch and measuring the compressed distance?

I didn't read your whole post. Scratch that last statement.

What starting point did you use for spring in the perch is a better question? Or are you just adjusting to get the ride height based on your calculations above?

Onefast V

iTrader: (3)

The KW is completely different than the GC because it maintains the stock rear suspension where as GC converts it to coilovers. And because GC relocates the spring to the shock mount, you cannot compare their spring rating because you have changed the elver arm and therefore two different spring could have the same effective wheel rate. therefore a 650# spring from KW is different then running a 650# GC spring.

CTSV_510

iTrader: (1)

Ground control doesn't relocate the rear springs. It just adds an adjustable collar to the upper spring mount, the shock remains separate

Onefast V

iTrader: (3)

For some reason i thought it convert the rears to true coil overs..oh well. my mistake

garrettg

iTrader: (1)

Just the high dollar penske and the LG Bilstein setups convert to rear coilovers. I don't know what rear springs those setups come with but would expect it to be much lower than the kw and gc kits.

Onefast V

iTrader: (3)

they up the front to 700# i believe and the rear to 400# on the LGs

Cadzilla

iTrader: (3)

Well I put the 600/650’s on this weekend. First, I was way wrong about slamming it in the rear with a 10” spring. I can’t get any lower than 26.5 with this 650# spring and I know im not riding on the bumpstop, so fuzzy is right about the shorter spring if you are going that high on the rates and want a ridiculous drop...personally 26.5 is as low as I’ll go anyway, the fender is right at the tire edge but not overlapping, so I’m happy with it. Just wanted to change that feedback in case someone took it as fact.

Anyway, huge improvement over the 500/550 with the qa1s. I’m still not set on keeping the qa1s unless I can get it dialed in better but at least I don’t feel like they are completely worthless now. I spent most of my lunch today driving around and adjusting them stiffer and stiffer…still not right yet. I have about 50% more clicks to go before they are on full stiff. I’m running out of patience for these f*** adjustable shocks. I still can’t see the benefit unless perhaps I lived in central Kansas, and the rebuildable aspect…but that doesn’t help if you don’t like the product to begin with. With fg2s, the gc 500/550 is a VERY good compromise between stock and firm. I would NOT recommend qa1s with a 500/550 setu (or “stock” qa1s with any setup for that matter).

I still can’t take a ‘quick’ corner hard, it just isn’t balanced. For whatever reason, I can’t get the rear to rotate at all, and the back end hops/skips some... I know this is due to the firmer springs and of course im on city streets most of the time so I can’t get too crazy, but it understeers more than I expected. The one thing I liked about the stock, or pseudo stock setups, was that 100% safe, predictable rotation…now it feels like I’d be glued until it let go and I would fly off the road. I’m going to switch the rear sway to the stiffer setting and see if that helps, but it may just be a characteristic of the firm shocks/springs. I need to hit some “closed” roads and discover where it lets go now.

One other thing I did is firm up the cradle bushings pretty good…I love the feel….but it may just be too stiff with everything else going on. Luckily what I did is reversible so I might have to change that too..

So shocks aside, the 600/650 spring rate isn’t too firm or rough at all, but it is quite different than stock and might be too “stiff” for some. I believe the V was meant to have a ride this firm and I happen to love the road feedback you get from these stiffer springs… I just hope I can get it dialed in with the qa1s or I might find myself wasting almost another grand just to get the ride I want from the car. With the fg2s, I feel the 500/550 was just as firm from a body roll perspective, as the 600/650 and qa1s, probably because of the

Skidmarcx

Thanks for the feedback I'm on the fence about getting stiffer springs or just waiting a while for some KW or LG coils... I realize my shocks are going to be an issue

Cadzilla

iTrader: (3)

Nevermind

furbe

Only thing unreliable is the info you provide here. lol
Did you own a set of K-sport coilovers for the 2003-07 CTS and had some
problems?
People seem to trust you on this fourm so you should grt your facts kinda straight before you lay bogus info out there. Just my opinion.

I have the K-Sport coilovers (actually I have the D2 Coilovers which are EXACTLY the same as K-Sport. Same manufacture, same plant, same product) on my V1 and have had ZERO issues with the preformance OR reliability. Only thing I changed was the front springs to a 10 inch Hypercoil #625. [IMG][/IMG]

And I wouldn't say i'm easy on them,
[IMG][/IMG][IMG][/IMG]

I have no idea why you would have to buy End-Links?
My car came with end-links. Don't most come with end-links?
I have the STOCK end-links and have has ZERO issues!

As for K-Sport being incompatible with aftermarket rear sway bars, I have the stock sway bars but I seriously doubt you will have any problems with ANY rear sway bars

K-Sport (D2) are a good prodict for the money. You can get these for under
$1000 and I would recomend them.
And I actually HAVE THESE ON MY CAR!
Before these I had KW V3 on the same car.
Don't listen to unreliable info from someone who has never used them.

Cadzilla

iTrader: (3)

nice pic in the middle there!.. so your car doesn't bounce like a fkn pogo stick? Must be nice. And Ksports are <$1000?
Seems like you get what you pay for??: $250 Springs,random shocks < $500 GC kit, random shocks < K sport-$1000 < kwv3 $2xxx < LG $2xxx < Penske $4xxx <V2 $70,000 ?

The missing link is ride ride ride….can any of these produce a comfortable ride? Who knows. There’s a tradeoff with every change you make to the car.

You are right, there is all kinds of jacked up info in here, including mine....but I don’t claim to be right about anything so I’m exempt from responsibility for bad info.

--
So just to follow up, after researching more, I came to the conclusion that perhaps my sway bar might be binding, which apparently can greatly exaggerate the spring rate. Then I remembered that a couple months ago, instead of reordering more stock bushings for my stock front bar (I lost one), I used the new energy suspension ones I had for my eibach bar. Their inside diameter was too large for the stock bar, so I wrapped gorilla tape around the stock bar to take up the slack. In addition, I overtorqued the sway bar brackets, which, in combination with unlubed bushings, might have resulted in a bar that wasn’t rotating freely within the bushing. To test this theory I unbolted the endlinks from the swaybar and rode around. It steered like a zamboni but it was definitely WAY smoother and was ALMOST tolerable…at least it didn’t bounce like a slammed 1992 toyota truck anymore…

I returned home and ended up just putting the eibach bar back on along with lubing the hell out of the bushings. Took it for another drive. Much sharper steering than with the stock bar….good-, but as I remembered from before, effort to steer was greatly increased (in a bad way- ruts, crown, bumpsteer, etc), and worse, the pogo was back…so I clearly need the least intrusive bar setup possible so I’m going to order new bushings for the stock bar and see how that feels. Or, maybe leave it and swap a 550 in the front and try to contain it with the qa1, or put the 650 up front and 600 in the rear.

At any rate I’m convinced the sway bar is the root of at least 75% of the problem. The rear just doesn’t pogo like the front . I read a lot about endlink angles and bar angles- - something to the tune of “ you not only want the bar neutral according to the rested ride height, the links should ideally be perpendicular to the frame, to make certain that the bar flexes only vertically when the car turns. If links sit at a lower angle, you’re then creating added spring rate with a horizontal flex” (or some **** like that). Also important that we lube the inside of the bushing (especially with poly) so the bar can move in its limited operating range without binding.

Im thinking I might have put the links on backwards at some time or another…IE on the driver side, staring directly at the link from the wheel well, should it be anged like this “ / ” or this “ \” ? same for the passenger side. Seems if I switch them the other way, the rested angle of the link might would be more up and down rather than angled. I presume this is what the main benefit of the z06 links is since once you lower, the distance between the mounting points dictates that you need a shorter link to maintain the optimal operating position.

I did notice that my eibach bar’s mounting points are a good bit lower than the stockers since the bar is angled differently, meaning that even when loaded, there’s less preload on the bar with the stock links. Maybe if I replace the stock links with z06 on the eibach bar, it will level out…too tough to call. I still want to try the stock bar with new links to see how that feels.

I just don’t want to ride on a fking pogo stick anymore. If it costs me $1000 to fix it, ok. If it costs $2000, ok. But I don’t want to F with it again for a WHILE. I just had a baby and my wife is getting very impatient with me,…women don’t understand when you spend 8 hours on your car, drive it, then say…,,”it’s just not right” LOL… I may have to resort to putting tools in my trunk and working on my car during my lunch time :/

FuzzyLog1c

iTrader: (4)

If you need 550 pound 10" springs, let me know. I've got a pair.