saw this on another forum might be usefull.. sorry if this thread was already posted before...


Thought this migt be useful to you guys.

The spring rate = (1406250 x d x d x d x d) / (N x D x D x D)

d = wire diameter in inches

N = Number of active coils.
The flattened coils at the ends are not considered active.

D = Mean diameter of spring.
Half way between the inside & outside diameter.

I've tried it for a few odd springs and it generally comes within 10% of what the manufacturer reckons it's supposed to be.

 

Such calculations only work when comparing different springs made out of the same alloy. It lacks a variable to account for material used.

 

I use a rate tester.

 

or u can use this http://hondaswap.com/reference-mater...n-chart-30786/

 

That is a conversion chart. That won't help you if you have an unknown spring in your hands.

 

How many springs are made out of alloys that aren't steel? The modulus of rigidity is the same within a fraction of a percent for every common steel alloy that springs are made of.

Here are a list of steel properties if you're interested: http://www.engineersedge.com/manufac...s_strength.htm

Modulus of Rigidity "G" is the same as Modulus of Elasticity in Shear which is shown in the table.

The spring rate equation with all variables is k=(G*d^4)/(8*n*D^3)
where k is the spring rate, G is the modulus of rigidity, d is the wire diameter, n is the number of active coils, and D is the average diameter (inside diameter plus wire diameter).

Given that G is about 11.4 million psi for steel alloys, that reduces the equation to:
k=(1425000*d^4)/(n*D^3), which is about 1.4% different than what the OP stated.

I'd say they were pretty close. This equation is good if you dont have a rate tester, but the tester that Bailhatch mentioned would be the most accurate in all cases (unless the force or length gauge on the rate tester is out of calibration).

-Tony

 

http://www.hypercoils.com/Suspension...Advantage.aspx

How common it is to use non-standard materials for springs for cars, I can't say, but it is something that needs to be considered if trying to calculate spring rate based only off of external dimensions.

 

This is why I gave the actual equation, which includes "G". The equation can only be simplified as shown if the material is assumed to be affordable steel.

Nice job with the citation, but if I had the money for titanium suspension parts, I wouldn't be modifying a Honda.