Originally Posted by
DaveW
I figured you would like that pic... clear and concise.
I was trying to relate it to something simple looking. It seems most are confused by all the coils on a shock spring... so i figured relating to a simple swaybar would help.
I mean... i could have thrown a curve ball and mentioned that a sway bar is actually dynamic... since it ties in BOTH sides of the suspension... lol
1.
YES
2.
FAIL Lets look at one side of a swaybar... a simple spring. When you shorten the leverage points the rate doesnt change... you increase its efficiency. Lengthening the leverage points decreases its efficiency. The wire STILL BENDS (notice i didnt say torsional twist) AT THE SAME RATE.
This is relatable to a BB spring and why it feels 'plush' or more 'consistent' than a regular AE spring. The BB spring is less efficient at doing its job than the smaller AE spring (and also one reason why the AE spring tries to move off axis... which also addresses efficiency... but i digress). This is also why a shorter lever on a swaybar increases response... its using the same rate and doing its job more efficiently.
3.
FAIL "As the number of coils decreases, the spring rate increases."
Really? So... youre telling me you have changed your mind with your previously posted...
"... when the wire diameter increases, spring rate increases."
Im not even going to get into your active/inactive coil theory... ill just leave that for you to think about.
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As far as the amount of coils in a spring... you will notice as a general rule that the thicker the wire the less coils there are in a linear spring. Also as a general rule... the more suspension travel, the greater the number of coils that will be present in any given linear spring.
You will see mix matched versions of this in various applications. Trust me though... if wire diameter does not change... neither does the spring rate... regardless of the amount of coils present... or how they are linearly implemented.
I know you (and i say that collectively... not pointing any fingers) have been told over the years that 'this' means 'that' but this is an opportunity to get the facts straight... and get some real insight on why something works as it does.
There is quite a bit of misinformation being thrown around here as fact.
The truth is that a compression spring's spring rate will vary by
4 parameters!
1. Wire Diameter (As wire diameter goes up, spring rate goes up!
2. Mean Coil Diameter (As diameter goes up, spring rate goes down)
3. Number of active Coils (As Number of Active coils goes up, spring rate goes down)
4. The Material Modulus of Rigidity (Modulous goes up, spring rate goes up)
Here is a great online spring calculator to demonstrate how each parameter influences the spring rate:
http://www.efunda.com/DesignStandard...igner.cfm#calc
or this calculator:
http://www.planetspring.com/pages/co...calculator.php
The equation for calculating spring rate is:
Spring Constant = k = ((d^4)*G)/ (8*(D^3)*N)
d= Wire Diameter
G= Modulous of Rigidity
D= Mean Coil Diameter
N= Number of Coils
[This information can be found in "Mechanical Engineering Design, 5th Edition" By Richard G Budynas and Keith Nisbett] **Attached is a scanned copy of the page**
The anti-roll bar analogy actually helps further prove this. The length of the lever arm of anti-roll bar just allows you to apply more torque to the bar given the same force.
However, if you will notice when parameters that effect the total length of wire are increased...the spring rate goes down. This is because you have more material to absorb that same energy and this is anologous to having a longer (wider) anti-roll bar. Where given the same torque on the end of a longer rod will result in a greater angle of twist of the rod. If you shorten the rod for the same torque applied to the end you decrease the angle of twist. Similar to a compression spring if you increase the diameter of a anti-roll bar you will increase the resistance/ spring rate.
In regards to progressive and dual rate springs, I can get into that on another post. But here is a link that talks about springs and even uses the SAME image that people were debating over in the B4.1 thread.
http://motorcycleinfo.calsci.com/Suspension.html
I hope this is sufficient material demonstrating the parameters that give you your spring rate!!