Lapping AtlantaMotorsportsPark in the CTS-V...Video
#4
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That looks like a great track! First video I've seen from there. I might have to see about making a trek down there for an event next year.
Last edited by AAIIIC; 12-04-2012 at 10:01 PM.
#5
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#10
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For what it's worth, I'll be posting a Ground Control build thread in the next couple of weeks with an aggressively tweaked dual rate Eibach spring package. Total cost will be about $1100 ($600 over the cost of the $500 Ground Control kit), but you'll be able to use the entire library of Eibach 2.5" springs to tweak the kit and use the springs that you don't need now later. And it's better than the D2 kit. Preview images:
![](http://img.photobucket.com/albums/v219/QuicksilverG4/CTS-V/DSC00402.jpg)
![](http://img.photobucket.com/albums/v219/QuicksilverG4/CTS-V/DSC00432.jpg)
- 3820 lbs without me in the car
- 4000 lbs with me in the car
54/46 weight distribution creates front corner weight:
- 1080 lbs front and 920 lbs rear
Assuming compression and spring rate change linearly for conservatism:
- 600/1300 progressive tender springs have 1.75" travel, starting at 3.55" unloaded to 1.80" at coil bind
- 600/1300 progressive springs require 1552 lbs loading to coil bind
- 1080/1552 = 0.6959 --> 1.75*0.6959 = 1.2178" compression, leaving 0.5" travel before coil bind
- 920/1552 = 0.5928 --> 1.75*0.5928 = 1.0374" compression, leaving 0.75" travel before coil bind
- 1300-600 = 700 lbs change in progressive rate
- 700*0.6959 = 487.13 + 600 = 1087 lbs effective initial rate
- 700*0.5928 = 414.96 + 600 = 1015 lbs effective initial rate
80 durometer Steele black X-hard spring rubbers inserted: somewhere around 50-100 in-lbs initially, ramping aggressively until full block. Generalizing: front is 1150 and rear is 1100 in-lbs with spring rubbers.
- 1150*800/1950 = 472 in-lbs effective front initial spring rate (800 in-lbs final front spring rate)
- 1100*850/1950 = 479 in-lbs effective rear initial spring rate (850 in-lbs final rear spring rate)
During that 0.5" front progressive spring travel, which requires 400 extra pounds load, the 800 in-lb front spring will also compress 0.5". This gives 1" travel before coil bind, less whatever the spring rubber provides. During that 0.75" rear progressive spring travel, which requires 600 extra pounds, the 850 in-lb front spring will compress 0.7" also. This gives 1.5" travel before coil bind, less whatever the spring rubber provides.
Theoretically, with the CTS-V's 4000 lb weight, 1800 mm width, and (if lowered) 600 mm center of mass, a 1.0G turn would transfer 1G*(600/1800) = 0.3G --> 1200 lbs load transfer (30% of vehicle weight) from one side to the other. Solving to figure out how hard I have to turn to lock out the progressive springs completely:
Greq_front = [400*(1800/600)]/4000 = 0.3G
Greq_rear = [600*(1800/600)]/4000 = 0.45G
I consider this an acceptable situation in a rear wheel drive vehicle, since I want to encourage a little bit of rear weight transfer to enhance grip while accelerating, and I want to keep the nose of the vehicle controlled to prevent air from getting underneath and bottoming out on bad roads.
Last edited by FuzzyLog1c; 12-05-2012 at 12:10 AM.
#11
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Better than the d2 kit is a very subjective comment. The Fe4 and fg2 shocks both lack compression and rebound adjustment. The d2 could be run with dual rate springs as well.
#12
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I agree--my statement was subjective. I value the longevity of the FG2 shocks over the D2 shocks more than I value rebound adjustment.
#13
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At the very least, you need to get the Hotchkis sway bar kit and adjustable end links. $600 and you'll feel like you have an entirely new car.
For what it's worth, I'll be posting a Ground Control build thread in the next couple of weeks with an aggressively tweaked dual rate Eibach spring package. Total cost will be about $1100 ($600 over the cost of the $500 Ground Control kit), but you'll be able to use the entire library of Eibach 2.5" springs to tweak the kit and use the springs that you don't need now later. And it's better than the D2 kit.
For what it's worth, I'll be posting a Ground Control build thread in the next couple of weeks with an aggressively tweaked dual rate Eibach spring package. Total cost will be about $1100 ($600 over the cost of the $500 Ground Control kit), but you'll be able to use the entire library of Eibach 2.5" springs to tweak the kit and use the springs that you don't need now later. And it's better than the D2 kit.
Edit:Wish I knew as much about springs as you, maybe in time. But what springs and rates did you settle on?
#14
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Ok so 1100$ for the ground control kit with the better springs and dual rate. +800-1000$ for new Fe4 or fg2's=1900-2200$ for this set up in reality. Which at that point you might as well go with some KW's (2400$) and have it all.
Edit:Wish I knew as much about springs as you, maybe in time. But what springs and rates did you settle on?
Edit:Wish I knew as much about springs as you, maybe in time. But what springs and rates did you settle on?
Everything you could ever want to know about coil overs, truly the coil over bible. they also have a great excel sheet to help you decide on spring rate for your car based on its geometry and corner weight, etc.
#15
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While i cannot comment on D2 longevity. I do know many FG2 have a propensity to begin leaking prematurely often <30K miles. I just cannot justify have to spend a minimum of $600 bucks to replace 1 shock because the FG2s are never sold individually. However your setup does look very intriguing and I commend you spending the time to find a good dual rate setup.
Last edited by Onefast V; 12-05-2012 at 01:43 PM.
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Also you need the high wind cover for your go pro!
Last edited by NIKDSC5; 12-05-2012 at 01:56 PM.
#18
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Ok so 1100$ for the ground control kit with the better springs and dual rate. +800-1000$ for new Fe4 or fg2's=1900-2200$ for this set up in reality. Which at that point you might as well go with some KW's (2400$) and have it all.
Edit:Wish I knew as much about springs as you, maybe in time. But what springs and rates did you settle on?
Edit:Wish I knew as much about springs as you, maybe in time. But what springs and rates did you settle on?
And I haven't settled on a recommended parts list yet, though I'm close. Right now, I'm running:
2x Eibach 0800.250.0800 linear primary springs (front)
2x Eibach 0600.250.0850 linear primary springs (rear)
4x Eibach 0175.250.1300 progressive tender springs (all)
4x Eibach COUPLER250 (forms primary/tender interface)
8x Eibach ISOLATOR250 (top and bottom of each coupler)
4x Steele 80A 2.50" spring rubber (locks out tenders earlier)
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