Spring rate calculations

[luvemfast]

Who here knows how spring rates are calculated?

 

Out of curiosity, I measured the the forces of the new and old rear springs at free and compressed lengths. I used a tensile tester and it gives me a Newton measurement.

 

Now how do I use this information to give me a spring rate? In either lb or kg

 

Example

At estimated ride height, the spring force/power was 2,490N (2.49kN)

I found a conversion calculator online and it converted to 559lb

Now I can tell you that is not correct.

 

Help

[stevo_gj]

Sounds like your measurement was in the ballpark to me. 1 ton car divided by four springs = 1,000 kg X 9.81 m/s^2 / 4 springs = 2,450 N (kg*m/s^2)

 

Springs are typically simplified as a linear increase for each unit of compression or tension, but in reality near the free length they can be highly nonlinear. Spring formula is usually F = kx, where x is the change from free length in meters, and k is the spring constant in N/meter.

 

If you are really keen, compress your spring at 10 intervals from the free length to operating length, and plot the measured force versus the compression length and you should see a graph that is initially non-linear, then becomes linear.

[Six_Shooter]

There are calculations based on measurements, that include wire diameter, mean diameter, number of active coils and a few other parameters. I have it in a book, I'll see if I can find an online example.

 

-=EDIT=-

 

IIRC, this is the formula I have used:

 

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

[luvemfast]

There are calculations based on measurements, that include wire diameter, mean diameter, number of active coils and a few other parameters. I have it in a book, I'll see if I can find an online example.

thanks Shooter

 

[Zedman240®]

I'll be using a set of bathroom scales, a lever against a wall and a measure. Compress the spring an inch while it's on a set of scales with the lever against a wall and see the weight. Crude I know..

[dat2kman]

There is a very accurate formula in the really old fashioned outdated old school suspension book by Fred Puhn.

"How to make your car handle"

 

In todays modern world this wouldn't be right, as like we dont need encylopeadia's anymore, as everyone is a expert and knows all!

[luvemfast]

Gordo emailed me this link.

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

Now all I have to do is go measure my springs 

[Six_Shooter]

Gordo emailed me this link.

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

Now all I have to do is go measure my springs 

 

Also in my post.

[MaygZ]

I'll be using a set of bathroom scales, a lever against a wall and a measure. Compress the spring an inch while it's on a set of scales with the lever against a wall and see the weight. Crude I know..

 

Do you really have bathroom scales that measure up to 300 lbs????

[lightmaster240z]

Yep and a forklift to move them 

[Zedman240®]

Do you really have bathroom scales that measure up to 300 lbs????

 

Some can be found...  with the way the world is heading they may become common..hahaha