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 Post Posted: Sat Jan 01, 2011 6:54 pm 
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Just a question on how to figure out what spring rate to use on a coilover shock.I suppose weight scales will have to be used to figure it out or is there another way?
Thanks in advance for any input.


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 Post Posted: Sat Jan 01, 2011 8:13 pm 
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Most ppl that sell springs will work with you if what you get isn't what you need as long as you don't hork them up before you send them back. If memory serves, Chassisworks and Chassis Engineering (and maybe some others) have spring rate calculators on their websites so I'd go there and take a look. Also some of the guys here (gearhead1011 for one) have a background in car construction and may be able to help.

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 Post Posted: Sun Jan 02, 2011 12:26 pm 
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How much does the car weigh? This a stock type chassis? How much of the cars weight is going to be on the coil over shocks? Are the shocks going to be on the rear or the front?

Don

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 Post Posted: Sun Jan 02, 2011 10:36 pm 
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want-a-be,the car weighs 2640 lbs. It has ladder bar suspension with coilovers on the rear.Not sure how much weight there is on the coilovers at this time.I just noticed the ride height has dropped about an inch from sitting over the winter.I thought maybe the springs may be getting a little weak.There aren't any leaf springs on the car either.
Thanks


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 Post Posted: Sun Jan 02, 2011 10:51 pm 
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Are you sure the tires aren't flat spotted from sitting? That, and is the air pressure where it is suppose to be? Don't usually have much of a problem with springs.

My Camaro is about 2450 lbs or so with me in it and I've got a 125lb spring in the rear of it. Rear corner weights were about 600 lbs or so.

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 Post Posted: Mon Jan 03, 2011 2:11 am 
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The spring rate is the amount of force in pounds that it takes to compress the spring 1 inch. There is a formula for figuring the rate on a coil over that takes into account the distance from the center of the axle tube, the angle (if any) and location of the shock (in front or rear of the axle). Of course you need to know the corner weights and how much of that is sprung. You should be able to figure out what you need by what is on the car now. Almost all coil over springs have a tag with the spring rate in lbs. If you can't find a tag if you measure the wire diameter and count the coils you can calculate the rate. You will need to figure out the installed shock height. This is the center to center distance of the shock mounting points. The most common rear shocks are 14". If your car has really dropped an inch from sitting you must have a very poor or too light of a spring to start with. I would suggest going up at least one on the rate from what you have. I would guess you would be in the 140-150 lb range.

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 Post Posted: Mon Jan 03, 2011 5:35 am 
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Some coil springs that don't have tags with rate on them may have it scribed on the flat part of the spring... :-s

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 Post Posted: Mon Jan 03, 2011 9:34 am 
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The car is sitting on jackstands with the tires off the ground so not an issue with flat spotting the tires and air pressure.I will drag myself underneath the and see if there are any tags on the springs and if not I will take the shocks off and see if there are any markings for spring rates on them.
Thanks guys for the suggestions.


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 Post Posted: Mon Jan 03, 2011 6:28 pm 
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It is so hard to select a perfect spring/shock because there are so many variables involved. The first thing to understand is the function of your spring/shock. It has 2 basic functions. 1 To support the weight of the car. 2 Smooth out any oscillations, to maintain contact compliance of the tire to the ground.

About any spring that doesn't coil bind will support the weight. The maintaining tire compliance does modify this a bit. So we have to input a few related facts. Spring location= a spring in front of the axle has to be more rate than one behind, to get same spring rate at the contact patch. Springs installed at an angle can increase rate after about 10 degrees, but they will reduce travel. Springs mounted too far inboard can loose a lot of roll control. This is not a problem with a latter bar car.
The surface you are running on has input also= More bumps the softer spring package needed. The instant center has input also.= At launch your IC determines what weight is carried by the spring/shock and what is carried by your anti squat. ( too much anti squat and you didn't really use the spring. Not enough and you have abused the spring. Power has input on springs. Ideal is to transfer weight to the rear, with out starting any oscillation, and if you go across any surface irregularities, it can smooth them out. Even the front spring/shock can influence what rear spring/shock is best. If the front gives up weight quickly, the rear has to control it by means of spring and shock and instant center. All this to put pressure on the rear contact patch smoothly and give it up smoothly.

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 Post Posted: Mon Jan 03, 2011 7:16 pm 
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superprocamaro wrote:
want-a-be,the car weighs 2640 lbs.
Thanks


I would run the 125 pound springs for that weight. How long are your shocks from eyelet to eyelet when totally extended? How long are the springs you have now when they are on the bench? How much engine do you have? How much chassis separation do you have with the springs you have now?

Don

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 Post Posted: Sun Feb 13, 2011 9:56 am 
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I got a brand new set of Afco Coils with a 125 spring rate if you need this rate!!!!!! good price too and lower than new ;-)

I agree with these guys too, and I fell into a trap in a way by listening to what my chassis guy said to buy, and it was these 125lb springs I have for sale too, they held up the chassis just fine, but when I set it on the ground, set the ride heigth with all the simulated weight in place, I didn't have enough shock shaft sticking out from what I would have liked, and there is a specific amount you need of the shock shaft inside the body, and outside as well per shock length, so remember to think about that also.

I now have 150lb springs and they ended up being PERFECT! \:D/ \:D/ \:D/ They hold the chassis up as needed and the ride heigth is still able to be adj. if needed but is where I want it at current time, and I got the correct amount of shock shaft in and out of the shock body, plus, it holds the chassis very well on the launch as I have my I/C almost is in the spot my chassis likes and I have hardley any chassis seperation, or squat if you can believe that, but my video's tell all. Like these guys have said, you need weights to really get you close as possible. If you do buy new springs, tape them up with masking tape or painters body tape so they don't get one scratch on them as what Ken said is soo true, if you scratch them, there yours to keep because YOU wouldn't want to get them scratched springs if you baught them new right?, that's how they think.

Good luck and let us know what you have for weights(if you can) and what you end up getting.

John

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