What spring length?

I have recently purchase a set of coilover shocks and am having a disagreement with the spring supplier. The shocks have 7" of travel so I assume the spring should have at least that much travel too, which when calculated out works out to a 14" long spring. The supplier sent me a 8" long spring and this is his reasoning which i dont understand.............
"A 7" stroke shock travels 7" no more. If the shock is mounted with no rebound travel it will travel in compression 7". The 8cs275 coil binds at about 4.75". No shock is ever run with no rebound travel. Normally shocks are run at an installed height to allow 60% compression 40% rebound. Taking that into account 60% of 7" = 4.2" travel for compression and 2.8" for rebound. That means the shock will bottom out well before the spring. Of course the actual suspension travel will be more due to the shocks being mounted at an angle. Or the spring and shock travel will be less because the shock never mounts 100% vertical and this travel will depend on the angle of the coilover."
Am i missing something?? please help.

Eric
Just trying to clarify.
You mention 7" of stroke, but what is the distance between platforms when shock is closed? Does it have an adjustable platform? If so what is max and min length between platforms when shock is in full bump, and max and min length between platforms when shock is in full rebound? Is it a 275 lb/inch spring? What is max and min length between platforms when fitted and car is at rest on its own wheels at ideal ride height? I assume shock is angled at about 30 degrees from vertical?
Lee

I havent finished designing the frame yet so there is nothing to fit the shock to. The angle if i remember right is around 60 degrees (suspension is from a C5 vette). You lost me with the rest of the questions so i will tell you what i do know. The shock is adjustable ride height. The entire body of the shock is threaded. Compressed length is 12.7", extended lenght is 19.8". Spring rate is 275 lb/in and 325 lb/in. Go here to see a picture if that helps, it is the 63 series shock. http://www.carrerashocks.com/ProductGallery.htm

My CAV springs in the front are 8" long, unloaded. The solid height (fully compressed) is 3.65". The car has about 4 1/2" of ground clearence. You will not use the full shock travel. You want the car bottom out before it hits the ground, so in my case 3" of compression is plenty. Spring rate up front is 275lbs.

My plan is to use a bump stop on the shaft to limit compression. I was going to use the springs anyways but the adjuster nut for the height is only about 1/2" from the end of the shock when it meets the spring, let alone having to do any adjusting it higher. I managed to contact someone at Carrera shocks and he says the spring should match or exceed the travel ability of the shock so it is off to try and return these and get the 14" long ones.

FWIW, here is the damper & spring from the rear of my stock GTD.

The damper is pulled out to the end of it's stroke.

Hope this helps.... /ubbthreads/images/graemlins/smile.gif

Julian, I was just about to take a shock off my GTD but I see you have one apart. If you would, could you post the following dimenions.

Center of top shock mounting hole to center of bottom hole fully extended.

Same as above except fully compressed.

Top spring perch face to bottom spring perch face with bottom perch set to minium ride height as in picture.

Lenght of spring, free of load, off shock.

Thanks, I will need to replace mine. 3 out of 4 have blown all the oil out. I have the same spaxs as you do. I think I will going to Koni's.

Thanks, Howard Jones

Brother JONES,

I have taken the rears off of mine and they are sitting in my Garage /ubbthreads/images/graemlins/smirk.gif /ubbthreads/images/graemlins/smirk.gif

I replaced them with the QA1 from Summit. So far so good.
I will make some measurments tonight /ubbthreads/images/graemlins/cool.gif

Howard,

Measurments as requested, (to within 5mm or so /ubbthreads/images/graemlins/smirk.gif)

Center of top shock mounting hole to center of bottom hole fully extended = 375mm

Same as above except fully compressed = 295mm

Top spring perch face to bottom spring perch face with bottom perch set to minium ride height as in picture = 260mm (fully extended)

Lenght of spring, free of load, off shock = 300mm

Hope this helps!

Julian, Thanks for the info, You saved me a couple of hours of work.
Howard.

Faili F

I see you opted for QA1 Shocks.
I am in the process of deciding whether to use the QA1 12 position adjustable aluminum bodied ones.
What ones did you use and how did they work out?

Kevin,

I purchased QA1s HAL-DR4855B shock (14"- 10 1/8") and HAL 10-350 Spring (350lb,10") for the rears. The fronts are still SPAX (until it starts to leak!)

I got it from Summit, I like them. The only thing that is not good about them is the maximum height is 14". Idealy 15" is what I needed (That is what the Spax were for the rear). My car sits pretty low so the droop factor should still be OK. At the present the ride height is set at 12 1/2" (Eye hole to eye hole,in the car)

Using the the shock you quote the compressed length is 10 1/8".
Is that enough travel ?? It looks like about 2 3/8" inches ???

Kevin,

Perhaps I should have explained better. 10 1/8" is the shock fully collapsed (without the spring).

When the shock and the spring are installed on the car (Under load), you will never reach 10 1/8" because of the spring.
Go to Summit Racing website and check out the numbers I gave and you can see better what I am refering to.

All, my car was spec'ed with QA1 (used to be HAL) DR4855P-1 shocks that are 12 way adjustable and 250lb 10" front springs and 350lb 10" springs in the rear. I have heard that these aren't proper shocks. Any comments?

The shock number you mentioned is the same one I use on the rear except your number is -P (poly), -B (bearing). I am happy with mine.