Factory Front and Rear Spring Rates???
 

Hi all,

I am trying to find what the factory spring rates were that came with the car (2560). I have a verbal that they are 600, but I am just trying to verify that.

Thanks,

Ken M 2560

Ken...give Dennis Olthoff a call at 800-297-6253. If anyone knows the modifications from car number to car number, it's Dennis. Tell him I sent ya...then be prepared for the lies he will tell about me. :3DSMILE:

Let us know the answer.

Thanks.

I find that hard to believe; my 351W SPF had 375# fronts and 375# rears, and they were stiff for the car. Weighed 2540#.
My current FRP460 SPF has 450 fronts and progressive rate 225/475# rears, 2750 lbs. Weights are with 3/4 tank and 160# driver.

The coil spring rates are usually stamped on the spring, either on top of the first coil (you'll have to take them apart), or screen-printed onto the side.

The 600# springs are way too big for that car IMHO.
Please let us know what you find out.

It sounded high to me too, but I did not know what the Motion Ratio was when I got the car and that's what the dealer told me it was.

I was advised today that springs that had been taken off other cars and tested, ranged from 350-375.

Ken M 2560

Just for a reference, after doing some extensive calculations and the use of some 4 wheel scales I am running 700# springs on the rear and 600# springs on my front. This was set up by a race team and to be honest with you the weights surprised me as well. But, the car handles very well at speed in the corners. Anyone want to buy some 500# springs :)?

Clois Harlan

Clois,

What other mod have you made to the set up? It seems you would get a lot of oversteer with those sprint rates. Did you install a larger front bar?

Thanks,

Ken

Explain to me the progressive rate spring idea.
Say a 225/475# described above. Does it operate closer to 225 for a more comfortable ride until pushed hard then you engage the stiffer part of the spring?
Would that mean a 500# unit like Clois is describing would ride really stiff and harsh?

Signed,
The Spring Idiot

PS - I've always wanted to change the AVO's for the Bilstein's and thought I'd change the springs at the same time but maybe the two aren't that intertwined.

I actually agree with Clois but for track use. QA1 has a progressive spring that's 180/600 that's recommended for front track use.

On the street, my progressives give me a nice comfortable ride over small bumps and undulations but grip tight when the springs compress probably around an inch or 2. Perfect for the street with the occasional stop sign bravado.:LOL:

Ray,

Who makes the progressive springs that you've got now?

I don't know what 2293 has, but I do know that SPF's come with the same spring rate regardless of the motor choice. If these new twin boys will ever let me get enough sleep to drive the car again new springs is on my list of things to do :3DSMILE:

Then again I'm pretty broke after all the diapers :CRY:

Daryl

Coil Spring Rate Calculator
 

This should help you get an answer to your question for your car. It is a coil spring spring rate calculator courtesy of jbl. It appears to be dead on from the tests I have given it.

Measure your spring wire diameter, the spring outside diameter and the number of coils. Enter the data in the blank fields push compute and shazam you have a spring rate.

Here is the link to the calculator => http://www.jblmotor.com/spring.htm

For what it is worth you might want to do a little lab experiment on a nice riding daily driver. Find a 200 lb friend, place him on the front fender of your nice riding daily driver. Measure how far the wheel well top lip settles with your friend on the car. Divide his weight (200 in this example) by the amount the fender lip settled in inches. You now have the spring rate for that wheel.

When I did this experiment I had a 4600# daily driver that was a little north of 1100# on the wheel I measured. My daily driver spring rate was about 220#/inch.

What you will probably discover is that your nice riding daily driver will also have a spring rate of about 225#/inch give or take 25 #/inch. This is no accident. This type of springing gives that comfortable around town ride on most 2 ton vehicles.

Now get yourself one of the progressive rate springs like QA-1's 200/600 progressive and you get the boulevard ride with race track handling when you woof on it.

By the way don't forget your Cobra is about a ton less massive than the nice riding daily driver so don't be squeamish about what seems to be a wimpy 200#/inch initial spring rate. The progressive will come in quickly maybe more so than you expect.

If you have access to a good suspension dynamics shop they can help you further tune the suspension including sway bar rates.

Enjoy.

Ed

QA1's website is http://www.qa1.net/motorsports.html

Daryl, here's the progressives page from QA1's catalogue (which you can download from their site). Congrats on the twins, they're a gift; enjoy them.
Get a better price from either Summit or Jegs after you get the SKU #s.
The 12" length for the rears was too soft. I used the 10" I intended to use for the fronts. I had a problem compressing them to install. Of course, I had already installed them in the rear with 2X 1" spacers from QA1 when I figured out how to do it..:LOL: So, I'll get another pair or maybe go for the 180/600 for the front.

[IMG]http://www.clubcobra.com/photopost/d...ogressives.jpg[/IMG]

Had mine done last year at CUSTOM ALLIGNMENT in mountain view CA. They specialize in race prep. Went with 350 fronts and 300 rears as the car was way oversprung. handles much better as it now bites in the corners and out of the hole hooks up much better as the weight now transfers to the rear. Running 351w cast block, alum heads. The car used to get real squirly in the corners as the back always wanted to pass the front and now it just turns. Still trying to test the limits as I know when it breaks loose it goes real quick! Make sure you have the car corner balanced also as this is a must for good handeling.

Fronts......EIBACH 8-350-225
Rears.......EIBACH 9-300-225

Just my 2 cents.
Greg

They come with 350# from the factory!

Another possibility is a "soft spring, stiff anti-sway bar" set up.

Somewhat related. I found an intersting tech bulletin on SCOF showing optimium suspension height adjustment. It even breaks it down depending on the size of wheels and tires you have.

Spings, bars, etc.
 

I hope this isn't too long and boring but maybe it will help. There are many other factors that effect handling like front and rear camber, weight distribution, tire and wheel size, geometry, toe, roll axis, CG ect. but this should help with spring selection.

The important factor is not the spring rate, it is the front and rear wheel rates that determine how any car behaves. The motion ratio of the suspension (the amount the spring moves vs. the wheel movement) squared times the spring rate gives you the wheel rate. If your car has a motion ratio of say .7 and a spring rate of 600 pounds your wheel rate will be 294 lb/". Anti roll bar rates are typically under 30% of the wheel rate to keep from lifting the inside wheel in a corner (at least in a narrow car like a Cobra). You can balance almost any spring rates front to rear so the car is neutral, the important factors are ride quality and grip on rough surfaces. The shock also needs to be matched to the spring rate and unsprung weight to achieve the best overall performance.
The anti roll bars and front to rear ride height ratio can be adjusted to achieve oversteer, understeer, or neutral handling if the front to rear rates are close to optimum for the particular car. My front springs are 200 lb/" higher than my rears but the wheel rate is higher in the rear than the front because of the higher rear motion ratio. A crude check can be made by placing the car on 4 wheel scales and then jacking the front and rear up with two floor jacks placed at the chassis center line simultaneously, one in front and one in back. You jack the front up .5", jack the rear up .5" and then take scale readings. The change in readings is what you want, if it goes from 650 pounds to 600 pounds in .5 inches of movement your wheel rate would be 100 lbs/ in
Repeat this process until you get 3-4 scale readings (1-2") and you can determine front and rear wheel rates. If you have a calculator you can then determine your motion ratio by dividing the wheel rate by the actual spring rate (printed on the coils of Eibachs and etched on the ends of Hypercoils). Take the square root of that number and that will give you the approximate motion ratio for the car at that location. Once you know your wheel rates it can give you a basis for making spring changes and keeping your car neutral when you make a change. All you need to do is select springs that maintain the existing front to rear wheel rate ratio. This is assuming you like the way your car handles. If you don't like it, upping the front wheel rate will increase under steer, upping the rear wheel rate will increase over steer, the reverse is also true. Shock rebound should also be increased with increased spring rates. All This is a very general and may not apply in extreme cases of wheel rates, but it should help guide your selection. There are a number of programs that will calculate anti roll bar rates, just keep in mind that they should be under 30% of wheel rate and should maintain the front to rear balance once you have an optimum number.