psychobillycaddy

iTrader: (4)

I need help setting the rebound on my D2's. How many turns and from right or left for the street? I keep rubbing every time I hit a dip in the road.

I had a corner balance done I just need to stiffen it up a bit

FuzzyLog1c

iTrader: (4)

Rebound doesn't control that. It's compression. Additional reading:

http://forums.nasioc.com/forums/showthread.php?t=150736

More advanced reading:

http://www.theoryinpracticeengineeri...sic_damper.pdf

Please note that compression and rebound damper settings (at least on the KW Variant 3, which has independent low and high speed valving) only affect low speed operation of the shock absorber (i.e.: less than 1 or 2 inches of travel per second).

If you're hitting bumps that are causing you to bottom out faster than that, you'll need stiffer springs, and higher damper settings to control them.

If your compression (read: compression damping) is set too high, or your springs are too stiff, it will feel like you're running no suspension at all (bumps will be harsh and punishing) because any upward motion of the suspension will be transmitted to the frame of the car. Conversely, if you don't have enough compression damping, the suspension will travel too far with little input, resulting in a floaty feeling. As a result, braking and acceleration will feel erratic and uncontrolled.

If your rebound (read: rebound damping) is set too high, or your springs are too soft, the suspension will not be able to return the wheel to its original position quickly enough to maintain traction. In other words, the springs aren't being allowed to move the wheel fast enough to follow the road. Conversely, if you have too little rebound damping, the springs will dominate the suspension; the wheel will carry too much momentum on the return path, overshoot, and come back. This will create a bouncy feeling, because your suspension (and by extension, the entire car) will tend to oscillate after each disturbance.

---

^The above was characteristic of my CTS-V with the Ground Control kit and 650-750 in-lb springs. Since the FG2 rebound was tuned for the OEM spring rates (350-450 in-lbs), rebound damping on my car with the GC kit was woefully insufficient. Regular, small-ish bumps in the road always resulted in 2-4 oscillations before the suspension reached static equilibrium. On certain roads, the car was almost always unsettled, and it drove me nuts.

Onefast V

iTrader: (3)

The d2 combines compression/rebound adjustment. I believe the springs provided with the kit are too soft (~550/550). I had the same issue as you with bumps causing rubbing and excessive suspension is oscillation. I purchased summit racing's 600/650 spring and they feel much better matched with the car. I am running 8 click back from hardest up front and 7 clicks in the rear.

Lt1junkie

iTrader: (9)

I'm fairly low just had fenders rolled & running 8 clicks back from all the way to right. Great ride

psychobillycaddy

iTrader: (4)

thanks guys Ill try that out. I put it at 3 from the right and its still rubbing. Ill try lifting the front shock a little to see if it helps. I might need stiffer springs due to the EForce weight on the front

psychobillycaddy

iTrader: (4)

Im guessing your running 600 up front and 650 in the rear.

I have some swift 680 (12kg) and 560 (10kg). I have a set of Eibach helper springs. 250-500

Im thinking that with the weight of the supercharger up front, I should use the 10KG with helper springs up front and the 12kg in the rear.

The other option is the 12kg up front and 10 in the rear. Im not a suspension guru and dont really desire to be one. If you are then please give me some advice so I dont have to go figure it out.

My corner balance came out to 1150 for the fronts with me in it and 975 for the rears. They had to lift the back up to get it there so I have major rake in the car. Hope that helps

FuzzyLog1c

iTrader: (4)

4250 lbs...wow. That's 400 lbs over stock. If you have a lot of rake, I'd consider trading that off (translation: lower the rear end) for better weight distribution.

psychobillycaddy

iTrader: (4)

Well I weigh 280 of it. The theres the E-Force and the GForce 9, spare tire and meth tank. It adds up.

He said he had to raise the rear to get more weight towards the back. Is that not accurate?

Onefast V

iTrader: (3)

10kg is exactly what the stock D2 spring are. I would get the summit springs ($35/ea). I am running 600 up front and 650 in the rear. I really think this is the absolutely minimum rate you can run and not have rubbing issue with big bumps. I have an mp112 up front which may not be as heavy as the e-force but im sure its not too far off. Is your major rubbing issue up front or the rear??

psychobillycaddy

iTrader: (4)

Up front. Can you send me a link to what you ordered. Ill go that route

psychobillycaddy

iTrader: (4)

I found the summit springs. The D2s are 10 inch springs correct?

Onefast V

iTrader: (3)

Based on a quick look using your corner weights. You should be running even a little stiffer than myself between 650/700 and 700/750.The D2s are 10 inches in the rear and 8 inches up front.

Here are some links for a 650/700 setup:
http://www.summitracing.com/parts/ei...0700/overview/
http://www.summitracing.com/parts/sum-92-5650



However to get the rates I wanted I went a little unconventional and went 10 inches up front and 9 inches in the back. Still allows me to go quite low with 275/35/18s up front and more than high enough in the rear (if i wanted too).

http://www.summitracing.com/parts/sum-102-5600 This is what I am running up front.

http://www.summitracing.com/parts/sum-92-5650 this is what I am running in the rear

FuzzyLog1c

iTrader: (4)

There's nothing unconventional about using 10" springs in the front and 9" in the back. Use whatever length/rate combination you need to arrive at the height you want with the rate you want.

That said, I would stay away from QA1/Summit brand springs. Reviews online indicate that their rates are known to deviate by up to 10% from the factory and they have a tendency to be inconsistent from inch to inch of compression by 10-15%.

Swift >> Hypercoil >> Eibach >> everything else.

psychobillycaddy

iTrader: (4)

Im going to go measure the swifts I have now and see how long they are.

I could use the 12kg up front and buy stiffer ones for the rear.

Would the eibach helper springs make a difference on top of the 10kg by increasing the rate?

FuzzyLog1c

iTrader: (4)

A helper spring is used to keep the main spring tight between the perches when the suspension is at full droop. It has effectively zero rate (actually more like 10 in-lbs). Having a stiffer helper spring is not going to change anything--it's designed to have no effect on the suspension.

A tender spring, on the other hand, is a spring that looks like a helper spring, but its purpose is different. It has a much higher rate than a helper spring (150-300 in lbs), and is designed to work in conjunction with the main spring to provide a progressive-like spring response. This works as follows:

Two springs in series always have a lower rate than either individual spring, as defined by 1/K3 = 1/K1 + 1/K2. In other words, a 600 in-lb main spring and a 250 in-lb tender spring stacked on top of each other would have a combined rate of 176 in-lbs until the tender reached coil-bind (locked out)--leaving you riding on only the 600 in-lb main spring.

As I found with my Eibach / Ground Control experiments, it's really hard (meaning: you'll land yourself in the poorhouse) to achieve a really nice ride this way--mostly because the weight and 54/46 weight distribution of our cars makes it hard to find the right spring rate and length combination. At that point, you're buying eight springs at a time, and if the weight of your car changes significantly, you've gotta buy them all over again.

Onefast V

iTrader: (3)

Anytime you add another spring your you effective rate is (Spring rate 1 * spring rate 2)/(spring rate 1 + spring rate 2). So two 550# spring in a dual setup would act like a 275# single spring. you can always run a dual rate setup but it would require more thought about which spring rates you want to use.

FuzzyLog1c

iTrader: (4)

Correct. That equation is a simplier version of the equation that I posted earlier. However, it only works for systems that have two springs. You could (and some people do) expand the earlier equation to account for systems of three springs or more:

1/Kn = 1/K1 + 1/K2 + 1/K3 ... 1/K(n-1)

psychobillycaddy

iTrader: (4)

I was just trying to figure out if I could use what I have. I have a set of Eibach tender springs that are like 250-500 (I would have to go look up what ichpen had). Ill just buy two more 750 swift for the rear and run the 12kg up front.