Progressively Wound Springs...

[macaroni 17 1 Cars]

Which way up should progressively wound springs go?

 

Tigher coils on the bottom or the top? Or does it even matter?

[PumaRacing 1]

What factors can you think of that would affect the way the spring works depending on its orientation?

[Bono 0]

from what i did in basic physics at gcse suggests it doesn't matter, however i get told time and time again it does

[jonnie205 1]

I got told different theorys about this too. I would have thought it would have made no difference but i cant say for sure

[Bono 0]

well you could argue the tighter coiled end would be slightly heavier so should go lower to keep the centre of gravity down

[GLPoomobile 958]

On the one hand I'm thinking it doesn;t matter, but on the other I'm thinking tighter coils at the top.

 

The compression is occuring in an upwards motion from the base of the spring. The force is acting upwards. So surely compression must occur at the base of the spring first, and therefore the softer end of the spring should be at the bottom to absorb smaller bumps more softly.

[Rippthrough 98]

On the one hand I'm thinking it doesn;t matter, but on the other I'm thinking tighter coils at the top.

 

The compression is occuring in an upwards motion from the base of the spring. The force is acting upwards. So surely compression must occur at the base of the spring first, and therefore the softer end of the spring should be at the bottom to absorb smaller bumps more softly.

 

 

Nope, the force acts equally from both ends otherwise there would be no compression. Other than the negligable effects on CoG and the like, which wouldn't be noticable even if the springs weight 100x as much, I don't think it matters.

[GLPoomobile 958]

Nope, the force acts equally from both ends otherwise there would be no compression. Other than the negligable effects on CoG and the like, which wouldn't be noticable even if the springs weight 100x as much, I don't think it matters.

 

 

Oh yeah, fair enough, the FORCE acts equally at each end, but wouldn;t compression occur from the bottom of the spring upwards?

[Rippthrough 98]

Oh yeah, fair enough, the FORCE acts equally at each end, but wouldn;t compression occur from the bottom of the spring upwards?

 

It'd occur where the spring is softest - at the most tighlty coiled part, doesn't matter where its mounted.

[GLPoomobile 958]

It'd occur where the spring is softest - at the most tighlty coiled part, doesn't matter where its mounted.

 

 

Oh yeah, that occurred to me after I posted I'm so gay sometimes

[macaroni 17 1 Cars]

So, it doesn't matter?

 

Is Mr Baker going to provide an answer, or just ask a question?

Strange, you'd think he knows the answer to this...

[Rippthrough 98]

I'm so gay sometimes

 

are we allowed to agree?

[petert 550]

Here's an even better one to think about - rear anti roll bars. If you had a 25mm ARB, which was necked down to 20mm to fit the splines on each end, what would be the resultant effective diameter? ie is the resistance to torsion the same along its length, so 25mm is the stiffest? Or will it fail at the thinnest section first, effectively being only 20mm in diameter? Or, does it behave like a progressive spring?

[Rippthrough 98]

Here's an even better one to think about - rear anti roll bars. If you had a 25mm ARB, which was necked down to 20mm to fit the splines on each end, what would be the resultant effective diameter? ie is the resistance to torsion the same along its length, so 25mm is the stiffest? Or will it fail at the thinnest section first, effectively being only 20mm in diameter? Or, does it behave like a progressive spring?

 

 

It would behave slightly like a progressive spring. But I imagine there'd be a fair amount of stress on the unsupported necked area, which could result in failure should there be a material defect, 25>20mm is a big step.

Hence the cost of torsion bar material

 

-Phillip

Edited August 8, 2006 by Rippthrough

[petert 550]

The torsional force must be equal along it's length, so therefore the stress must be greatest where the diameter is smallest - from I= d^4/32. As said, it can only behave like a progressive spring up to the point of plastic deformation or break point. A progressive spring will go solid, before the yield point is reached. An ARB, thus described, must surely fail at the smallest diameter. So why do people make and sell them like that? Am I missing something?

 

Torsion bar mat'l isn't expensive. It's the cost of machining and heat treatment.

[Rippthrough 98]

So why do people make and sell them like that? Am I missing something?

 

 

Because it will still give an increased overall spring rate.

[TEKNOPUG 3]

Surely it's progressive at both ends? IE: tighter coils at both the top and bottom of the spring. And therefore it doens't matter which way up it goes?

[macaroni 17 1 Cars]

No, these springs are only more tightly coiled at one end.

[Fuqa 0]

the coils that are closest together should be placed at the bottom

[tom_m 0]

it only matters if it is designed to fit a specific spring pan. as far as springyness is concerened it matters not

 

db's question is rhetorical is it not?

Edited August 8, 2006 by tom_m

[PumaRacing 1]

it only matters if it is designed to fit a specific spring pan. as far as springyness is concerened it matters not

 

db's question is rhetorical is it not?

 

Nope. I wanted to see how people apply their intellect to what is essentially a fairly simple physics problem before saying anything myself. Can't see much value in just handing out answers if people aren't prepared to think for themselves.

 

A progressively wound spring will certainly act differently depending on which way round it is fitted but only under certain conditions. Work out what those are and the answer should become self evident.

 

Hint. How might an engine valve spring, a suspension spring and a stationary spring designed to just apply a constant load differ from each other if they are progressively wound?

Edited August 8, 2006 by PumaRacing

[Batfink 201]

ok I would say the tighter coils will be at the bottom. This is because you only want the tighter coils to give a stiffer spring rate under the continuous compression under fast cornering and a greater load is applied. When the shock is acting to resist bumps you want it soft.

[Fuqa 0]

ok I would say the tighter coils will be at the bottom. This is because you only want the tighter coils to give a stiffer spring rate under the continuous compression under fast cornering and a greater load is applied. When the shock is acting to resist bumps you want it soft.

 

totally agree... thats why they are called progressive springs !

[PumaRacing 1]

ok I would say the tighter coils will be at the bottom. This is because you only want the tighter coils to give a stiffer spring rate under the continuous compression under fast cornering and a greater load is applied. When the shock is acting to resist bumps you want it soft.

 

You appear to think that a spring will compress at one end first depending on which end moves. How can the spring possibly know which end has moved and which hasn't?

 

Also you haven't even got the basics of spring rates the right way round. it's the widely spaced coils that give the higher spring rate not the tightly spaced ones.

Edited August 8, 2006 by PumaRacing

[Batfink 201]

hmm but then thinking about it - the force is applied to the whole spring and the spring does not react any different whether the force is applied from the top or bottom. The result will be exactly the same

 

So under small loads the tighter wound part of the spring will flex first and provide a softer ride, but under greater loads the increased load will cause the spring to compress more, the tighter wound springs will touch and effectively increase the spring rate.

 

Something tells me that the damper needs to be considered and if I add that into the equation I'd go with the tighter coils at the bottom though i havent really looked into the design of a damper - as compression of the rod is increased is there a greater resistance?

 

edit: Dave - sort of came to the conclusion about direction - slow typing means you posted before me lol - damn!

Edited August 8, 2006 by Batfink