How to best determine spring rate on an unmarked spring?

[Chris_Swearingen]

I have a set of springs with NO/NADA/None markings on it. I was told they are 400lb springs. So to verify this can stand on it and measure the amount of compression and divide by my body weight. Assume for a moment that I weigh 200 lbs, should a 400lb spring compress 1/2 inch? The spring does not appear to be progressive so that should work right?

[Donnie]

try this

http://www.stockcarproducts.com/pstech10.htm

[Randy]

For a spring F=kx where F is the force of the spring (i.e. your weight because its producing an equilibrium with your gravitational force), k is the spring constant (spring rate) and x is the displacement from equilibrium of the spring. So yes, your right a 200 lb load on a 400 lb spring should cause a compression of 1/2 inch. Hope this helps.

[Chris_Swearingen]

try this

http://www.stockcarproducts.com/pstech10.htm

Thanks,

Wire Diameter Spring OD ActiveCoils Rate
.4375 3.1875 6 412.88..... Unknown spring
.4375 3.375 7 290.36.... Eibach 250lb spring

So allowing for my calipers to be off and me to round the 16ths a little it looks like the spring is indeed at or near my 400 lb target.

[00 SS]

The number of active coils can be tricky. You need to count partial coils as well to be accurate. So your 7 active coils on the eibach could be 7.3 or 6.9 etc. Basically start at one end and begin counting full revolutions from the first part of the wire not touching the perch and add the partial revolution at the other end to the last point not touching the perch.

Hopefully your not calculating progressive springs, they get weird and have to be calculated at each .25" or so of compression and plotted to approximate the progressive curve. And if some of the coild start to go into coil bind be sure to recount the active coils at each interval.

[Jake Latham]

I've got a little JavaScript app to help with this:

http://www.jakelatham.com/radical/info/misc.shtml

-Jake

[geoffbp58]

Well, I personally think the most accurate way is to install the spring on the passenger seat of your car, then drive it to RPM Motorsports (13th and Wadsworth). Matt or I can put it on the spring checker! Works for me, anyway....(except my car has leaf springs)

[Chris_Swearingen]

Well, I personally think the most accurate way is to install the spring on the passenger seat of your car, then drive it to RPM Motorsports (13th and Wadsworth). Matt or I can put it on the spring checker! Works for me, anyway....(except my car has leaf springs)

That is probably the most sensible. Thanks for the offer. Unfortunately in this case, I live in the Springs, and have to assemble the car tomorrow. Based on the decidely error prone methods of stepping on it and measuring it, it appears to be close to what was advertised. At the very least it will be stiffer than the stock 164f/97r. The target was 425/250 but 400/250 will be close enough.

[EGbeater]

Well, I personally think the most accurate way is to install the spring on the passenger seat of your car

How many muffler bearings are required for proper installation? Oh shoot, that's probably going to be dependent on spring rate . . .

[Donnie]

it all depents on what turn signal fluid you use