Grassroots spring rate measuring?

I've got some mystery 2.5" springs, I want to see if they're of a rate that might be useful to me. What's an easy way to measure these with common tools?

And yes I've thought of "put some weight on them and measure how much they compress" but putting weight on them in a safe way is the tricky part.

First off, you hope that they are not rising rate...

Second, lever arm, a ruler, a calculator, and a known load.

Load it up with a known load and measure the deflection.

They're regular linear springs. Maybe I do just need to find a convenient lever arm.

Did some searching and found a formula to get a ballpark figure just by measuring the spring:

http://grassrootsmotorsports.com/forum/grm/how-do-you-measure-spring-rates/31227/page1/

GameboyRMH wrote: And yes I've thought of "put some weight on them and measure how much they compress" but putting weight on them in a safe way is the tricky part.

Use barbell weights and a length of pipe through the center of the spring.

k = Gd4/(8nD3)

k = constant, pounds of load per inch of deflection
G = modulus of rigidity of spring material, pounds per square inch (use 30k for steel)
d = wire diameter, inches
n = number of active coils, which is the number of coils that will flex It will always be less than the # of coils.
D = mean coil diameter, inches = Outer Diameter - Wire Diameter

That will work for any spring with a linear rate.

MadScientistMatt wrote:

GameboyRMH wrote: And yes I've thought of "put some weight on them and measure how much they compress" but putting weight on them in a safe way is the tricky part.

Use barbell weights and a length of pipe through the center of the spring.

Smart! That'll do the job.

Less work. http://www.pontiacracing.net/js_coil_spring_rate.htm

If you know the diameter of the wire, the diameter of the spring, and the number of coils (note this is independent of free length!) then you can calculate the spring rate.

I've used the spring rate calculators with pretty good success. I have also used a bathroom scale and a lever. Set the scale on top of the spring and use the lever to compress the spring 1". Read the scale.

Of course, if you have a 500-lb/in spring, a bathroom scale won't do much for you, but you could compress it 1/2" or 1/4" and calculate from there with varying degrees of accuracy.

No, no, no.... Just stand on it, against a wall so you don't fall off and have someone measure how much it compresses:

Spring rate = your weight / how much it compressed.