Isaacs

iTrader: (1)

Video from the trackday at Atlanta Motorsports Park this past Sunday.

FuzzyLog1c

iTrader: (4)

That track looks like fun! Shame that there was such a massive disparity in the quality of the cars out there.

Isaacs

iTrader: (1)

There were a few really impressive cars in the other run groups. It was a blast regardless, but now I feel the need to upgrade my suspension etc lol. It'll never end

AAIIIC

iTrader: (19)

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.

FuzzyLog1c

iTrader: (4)

What do you have right now?

01_SuperSlow

iTrader: (7)

Looks like a blast! I have to do that some day.
Willow Springs is about 1.5 hrs from me, I heard it's a good track.

Isaacs

iTrader: (1)

Stock Suspension

FuzzyLog1c

iTrader: (4)

Oof. No sway bars, bushings, or alignment?

Isaacs

iTrader: (1)

It's got an aggressive alignment and michelin supersports so it responds a little better than stock.

FuzzyLog1c

iTrader: (4)

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. Preview images:





- 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.

Onefast V

iTrader: (3)

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.

FuzzyLog1c

iTrader: (4)

I agree--my statement was subjective. I value the longevity of the FG2 shocks over the D2 shocks more than I value rebound adjustment.

NIKDSC5

iTrader: (10)

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?

Onefast V

iTrader: (3)

http://www.pirate4x4.com/tech/billav...lovers/Part_1/

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.

Onefast V

iTrader: (3)

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.

tmonttt

iTrader: (10)

I've contemplated going up to ATL a few times for this. Can you chime in on how much it was and about how time you physically spent on the actual track?

NIKDSC5

iTrader: (10)

+1 Man I have watched it 2 times now (high quality and low) and I cannot wait to be able to do this with my V someday. Especially after all the suspension/handling mods planned. Then again when I'm making more power!

Also you need the high wind cover for your go pro!

FuzzyLog1c

iTrader: (4)

If you already have FG2s, the cost of my setup is about $100 more expensive than the D2 Coilovers. I prefer Eibach springs, which have a million mile warranty to never change height or rate--a serious problem for cheaper products (like anything made by H&R). In total, there are probably less than 10 D2 coilover sets on CTS-Vs, so I'm loathe to spend $1000 on something with unknown reliability data. If they die on you 5 years down the road, it's unknown whether you'll still be able to buy replacements. Granted, we have similar issues with every product other than KW V3s, but at least I know my springs will work with any shock or coilover I buy. For almost every kind of car. I look at it as an investment.

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)

Isaacs

iTrader: (1)

This was a Toys for Tots event so it was very cheap($85) however there was probably close to 130 cars total. That equals very little track time since there were 6 different run groups. After a couple people went off into the sand trap and someone lost an oil line(all the way back to pit rd) we only got 3 20min sessions total. Usually its around $250, but you get WAY more time and it is WAY less crowded. You get what you pay for..