Progressively Wound Springs...

[Jrod 7]

Tighter coils at the bottom according to the manual for my progressive springs.

 

(they were for a motorbike though)

[petert 550]

Because it will still give an increased overall spring rate.

 

why though?

[PumaRacing 1]

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?

 

For starters you can't make a material in torsion behave progressively. Only a material in compression can do that. Well technically you can make a material in tension behave progressively but only by taking it past the yield point so kind of pointless if you want it to work more than once.

 

The torsion bar that's 25mm diameter along most of its length but 20mm at the ends will be stiffer than one that's 20mm all the way because the effective length of the bar has been reduced and spring rate is inversely proportional to bar length. However the stresses in the regions of reduced diameter will be high and prone to reaching their yield point. That reduces the life of the bar and it will eventually fail at the thinnest section.

[PumaRacing 1]

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?

 

Seems we're not going to get far on this unless I answer it. The answer depends on whether the spring is stationary or moving.

 

Under a given stationary load, any compression spring, however it's wound, will have only one resultant length. It makes no difference which end is moved. The amount of compression will always be the same under a given load because the forces are evenly distributed along the length of the spring. The spring rate curve might be linear if the coils are evenly spaced or progressive if the coils are unevenly spaced but once motion has ceased and the spring is at equilibrium there is no way the spring can know which end has just been compressed and which held static.

 

This all changes when the spring is moving rapidly under a varying load. For example a valve spring controlling the mass of the valve and lifter. Part of the spring force is being absorbed into controlling the moving mass of the spring itself. That's why a lighter spring material (titanium) will outperform a heavier one (steel) for the same static spring rate and allow higher rpm before valve float.

 

In this situation we want to minimise the amount of mass that's moving so that as little of the springs own force is being wasted controlling the motion of its own mass. We can achieve this with a progressively wound spring by having the closely wound coils at the stationary end and the widely spaced ones at the moving end.

 

In the case of a car suspension spring then the moving end would be considered to be the wheel and the stationary end the body of the vehicle. The spring would therefore be fitted with the closely wound coils at the body end (the top in a normal strut system) and the widely spaced ones at the wheel end. This maximises the amount of sprung weight in the system and minimises the amount of unsprung weight which is the ideal goal in any suspension system.

[petert 550]

For starters you can't make a material in torsion behave progressively. Only a material in compression can do that. Well technically you can make a material in tension behave progressively but only by taking it past the yield point so kind of pointless if you want it to work more than once.

 

Different mat'ls will behave differently in compression or tenion (eg cast iron or brass) but steel behaves exactly the same in compression as it does in tension. ie. the stress/strain curve is a mirror image. Thus you can have a tension spring or a compression spring.

 

But the formula for max. shearing stress, fs=TD/2J does not involve length, so please go on.

 

It is possible to determine the angle of twist, from angle=TL/GJ, but torsional shear occurs between "disc planes".

Edited August 9, 2006 by petert

[PumaRacing 1]

Different mat'ls will behave differently in compression or tenion (eg cast iron or brass) but steel behaves exactly the same in compression as it does in tension. ie. the stress/strain curve is a mirror image. Thus you can have a tension spring or a compression spring.

 

But the formula for max. shearing stress, fs=TD/2J does not involve length, so please go on.

 

It is possible to determine the angle of twist, from angle=TL/GJ, but torsional shear occurs between "disc planes".

 

The reason you can have a progressive rate compression spring by spacing the coils differently is because the closely wound coils eventually close up to leave only the widely spaced ones working. You can't do that with an extension spring because none of the coils stop working while they are below their yield point. However if you take a coil past its yield point and it straightens out to leave just a straight wire then you will achieve a higher spring rate in the remaining coils but the spring won't return to its original length.

 

The relevance of your various formulae to the point of the question eludes me.

Edited August 9, 2006 by PumaRacing

[Rippthrough 98]

But the formula for max. shearing stress, fs=TD/2J does not involve length, so please go on.

 

 

Because thats assuming a shear will occur across a flat plane.

 

Torsional stiffness is a function of diameter and length for a given material/shape. Essentially its stiffness is related as change in angle/unit length.

Hence the small length of the necked area + the 25mm area still gives a stiffer arb. The 25mm section will still twist because the small length of 20mm section esentiall renders it much stiffer than a full length 20mm section.

 

Not very well explained though, perhaps someone will have better luck with the wording.

[petert 550]

The relevance of your various formulae to the point of the question eludes me.

 

Sorry, the formulas relate to shafts in torsion, not helical springs. I mixed topics.

 

Torsional stiffness is a function of diameter and length for a given material/shape. Essentially its stiffness is related as change in angle/unit length.

 

Can you find a formula to support this? I haven't been able to find one.

[petert 550]

The internet has everything. After reading through all my books at work, it took me 2 secs. to find what I was looking for. Section 6.4: http://web.mit.edu/emech/dontindex-build/f...t/emechbk_6.pdf

[GLPoomobile 958]

I'm so gay sometimes

 

are we allowed to agree?

 

 

Certainly. But I'll come around your house and bugger you into next month

[Ahl 4]

This maximises the amount of sprung weight in the system and minimises the amount of unsprung weight which is the ideal goal in any suspension system.

I had that in mind. Wasn't sure if it was bollocks or not though.

[Rippthrough 98]

The internet has everything. After reading through all my books at work, it took me 2 secs. to find what I was looking for. Section 6.4: http://web.mit.edu/emech/dontindex-build/f...t/emechbk_6.pdf

 

 

The internet knows everything.

 

Certainly. But I'll come around your house and bugger you into next month

 

 

I'm washing my hair.

[Rob Thomson 6]

I was hoping the answer was because of unsprung weight because that was my assumption when I fitted mine, but I also assumed that because of the unsprung weight the closely wound coils should be at the wheel end of the strut.

 

I thought the progressiveness was due to the steel (differences in how it's been tempered along the spring etc) more than just the coils closing up.

 

I'd better go home and turn those springs round...

 

[subliminal]Dave, please build me an engine....[\subliminal]

[Rippthrough 98]

I was hoping the answer was because of unsprung weight because that was my assumption when I fitted mine, but I also assumed that because of the unsprung weight the closely wound coils should be at the wheel end of the strut.

 

I thought the progressiveness was due to the steel (differences in how it's been tempered along the spring etc) more than just the coils closing up.

 

I'd better go home and turn those springs round...

 

[subliminal]Dave, please build me an engine....[\subliminal]

 

 

If you've already got the strut together then i can see the point, the difference between the two is never going to be noticed, not with the unsprung weight the pug already carries around.

 

-Phillip

[Henry Yorke 269 3 Cars]

I just went the easy way on this... Eibach springs are progressive (and hot wound as well I believe). They have writing on the side so I figured, the Germans know what they are doing and they would find it illogical to have upside down writing, so fitted them that way!! Hey presto, small coils at the top and more spaced at the bottom.

 

Another reason to fit the smaller coils at the top is that if they get filled with dirt, then they will be less likely to get clogged up between the spring coils (which could impact performance) if the closer ones are nestled away in the top of the strut! (Guess who has had a rock stuck in a Landrover spring before )

[Rippthrough 98]

(Guess who has had a rock stuck in a Landrover spring before )

 

 

Every single Land Rover owner, ever?

[Henry Yorke 269 3 Cars]

Every single Land Rover owner, ever?

 

Now you know as well as I do that the majority of Landrover Discovery's never go off the road (or the school run!)

 

Oh and the answer was me

[Rippthrough 98]

Now you know as well as I do that the majority of Landrover Discovery's never go off the road (or the school run!)

 

Oh and the answer was me

 

 

Well it feels like it every time I hitch a lift in one

[mfield 20]

Guess who has had a rock stuck in a Landrover spring before

 

 

They have springs ?????

 

Every one ive been in feels like they have water bags for stability and the door handles serve two purposes, firstly to open the door and secondly when on the move they're there to protect the paint work from the kerbs.

[PumaRacing 1]

They have springs ?????

 

Every one ive been in feels like they have water bags for stability and the door handles serve two purposes, firstly to open the door and secondly when on the move they're there to protect the paint work from the kerbs.

 

Some years ago my car broke down and a friendly chap in the house I happened to break down outside gave me a lift back home in his Range Rover. It's the only vehicle I've been in where I've been s*it scared at speeds under 30 mph. It rolled so much round every corner I thought it was going to fall over. I have no idea why anyone would want to drive one of those things. They are desperately slow in both a straight line and round corners and carry less than a van. What's the point?

[Batfink 201]

because they are virtually indestructable

[macaroni 17 1 Cars]

That was probably before they were fitted with a rear anti-roll bar. Quite why they weren't from the outset is a mystery!

 

The only good Land Rover ever is the 90/110/Defender. One of the coolest, most single-minded-of-purpose vehicles ever. All 4wds since the LR are just poor imitations and, in my opinion, the latest rash of high powered poncy Chelsea tractors are just a bad, and expensive joke.

[Rippthrough 98]

That was probably before they were fitted with a rear anti-roll bar. Quite why they weren't from the outset is a mystery!

 

The only good Land Rover ever is the 90/110/Defender. One of the coolest, most single-minded-of-purpose vehicles ever. All 4wds since the LR are just poor imitations and, in my opinion, the latest rash of high powered poncy Chelsea tractors are just a bad, and expensive joke.

 

 

We pushed a bunch of trees down with a 90 to make room for someones garage, without causing any damage to the landie, try that with a poncy cayenne.

[Batfink 201]

Seems we're not going to get far on this unless I answer it. The answer depends on whether the spring is stationary or moving.

 

Under a given stationary load, any compression spring, however it's wound, will have only one resultant length. It makes no difference which end is moved. The amount of compression will always be the same under a given load because the forces are evenly distributed along the length of the spring. The spring rate curve might be linear if the coils are evenly spaced or progressive if the coils are unevenly spaced but once motion has ceased and the spring is at equilibrium there is no way the spring can know which end has just been compressed and which held static.

 

This all changes when the spring is moving rapidly under a varying load. For example a valve spring controlling the mass of the valve and lifter. Part of the spring force is being absorbed into controlling the moving mass of the spring itself. That's why a lighter spring material (titanium) will outperform a heavier one (steel) for the same static spring rate and allow higher rpm before valve float.

 

In this situation we want to minimise the amount of mass that's moving so that as little of the springs own force is being wasted controlling the motion of its own mass. We can achieve this with a progressively wound spring by having the closely wound coils at the stationary end and the widely spaced ones at the moving end.

 

In the case of a car suspension spring then the moving end would be considered to be the wheel and the stationary end the body of the vehicle. The spring would therefore be fitted with the closely wound coils at the body end (the top in a normal strut system) and the widely spaced ones at the wheel end. This maximises the amount of sprung weight in the system and minimises the amount of unsprung weight which is the ideal goal in any suspension system.

 

would this be the same for coilover helper springs? I just have a set built by eibach and they have the tighter coiled helper spring at the bottom

[johnrobertgordon 0]

Another Flex my brain muscles thread. Dont you find that when you follow them your baffeld and try your best not to post and ideas for fear of sounding like a twat. Then dave hits us with his answer and you sit there thinking "ohhhh yeeaaaa"

I love to hate these kinda threads, or should that be hate to love!?