Cut Springs- Stiffer? Softer? Same?

If a spring is cut in half what happens to the spring constant for the half spring

  • Total voters
    7
Noddie

Noddie

So i think this is an interesting discussion...
Maybe we could have a poll?

If one was to cut my springs in half, would they become stiffer or softer or just stay the same?

Answers below please (with reasons!!!)
links to websites with proof also welcomed

I plan to do a physical test within the next few days so maybe that will answer the question but until then maybe this thread will be a bit of fun.



I will start with my short workings (using the equations for adding springs in series).
where Kf is the spring constant of the full spring and Kh is the spring constant for the half spring...

yzy5ube9.jpg
 
So that maths/physics states it will get twice as stiff if they are half the size? Still a part of me that thinks they will have the same spring rate.... :/ Join MicraPro in being confused haha
 
I'm such a tit, you guys are right... doh. New game, spot the amateur mistake I made in the above sketch.
Hint: YOU CAN'T ADD TENSION OR COMPRESSION TOGETHER
:oops:
Energy in a coil adds that way, not force. In my defence, it's been what... 7? 8 years since I did my A levels?

On the energy note, the spring is only capable of absorbing half the energy if cut in half, so it's still only half as good at doing its job :rolleyes:
 
Enuo said:
I'm such a tit, you guys are right... doh. New game, spot the amateur mistake I made in the above sketch.
Hint: YOU CAN'T ADD TENSION OR COMPRESSION TOGETHER
:oops:
Energy in a coil adds that way, not force. In my defence, it's been what... 7? 8 years since I did my A levels?

On the energy note, the spring is only capable of absorbing half the energy if cut in half, so it's still only half as good at doing its job :rolleyes:
Click to expand...
Only just saw this lol. You spotted your own mistake so can ignore my post on your blog :). Though hats off for keeping it simple and avoiding kx etc... I haven't used that in ages either :p
 
Oh I did in some of the PM's I sent, feel like a right numpty now. Can hear my mechanics lecturers smug voice as he corrects me all over again haha
 
Never mind the maths....

Get a long bit of bar, bend one end 90 degrees to make a handle, put the other end in a vice and use your "handle" to wind it up. What did you manage, 90 - 180 degrees of turn on the handle? Now cut the bar in half and see how much you can wind it up, bet you cant wind it as far? So.... for the same force applied, there is less deflection - the torsion spring that you created and then shorted has a higher rate after shortening.

A coil spring is just a torsion spring wrapped up in a neat helical package, shorten it, you raise its rate.
 
Back to the spring thing ('cos I'm keeping Ginger for myself whatever you think), even though cutting them is fine and works very well, some cars just don't ride so well on cut springs. Generally, larger, heavier cars are more comfortable on cut springs, smaller cars do seem to be a bit more prone to jumping about on the road.
 
That's cause the change in stiffness is greater compared to the mass of the car and the original damping is way too soft to control it
 
In reality you want the softest possible spring rate without bottoming out the car, that way you can maintain good contact with bumps in the road surface:) anti roll bars are another matter.
 
That's the thing, mines on polo 6n and not even slammed, grips like magic but still scuffs on some bumps. But any stiffer would kill the handling... Humph!
 

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