Which way up for rear springs

[Landowner]

My old Disco rear springs are thicker at one end with tighter coils. I am going to fit them to my 90 but wondered if it made any difference which way up they are fitted.

Tighter coils to top when they came off

[Anderzander]

This was asked once before and the response that stuck in my mind was 'how does a spring know which way around it is ?'

So when I fitted progressive springs to the back of mine I made a point of putting them in how it best suited the spring retainer ..... But also explaining to then which way was up

[Landowner]

Thanks

I only asked so as I don't get slated for fitting them wrong way up when I put photos of built up chassis on

[Boydie]

Progressive rated springs are installed with the thicker coils at the axle and the thinner coils uppermost.

[Landowner]

Well...

I fitted them with the tighter coils at the bottom, tight fit for heavy duty retainers but sorted ok.

They were the other way up on the Disco with tighter coils at the top, dont know it that is standard fitment, perhaps someone could have a look at theirs for me.

they look ok anyway

[Ex Member]

I does not really matter... But the correct way is the tighter coils at the top. There are two reasons. 1) Slightly less unsprung mass.... 2) Less chance of rocks getting stuck inside the springs.

[Boydie]

The spring dynamics of progressive rated springs are that as the vehicle comes down, the tyres are onviously the first shock absorber to come in contact with terra firmer, as the chassis settles down the thinner (read upper coils) sections initially compress as the weight of the chassis and body obey the rules of gravity, as the rate of compression increases above that of the thinner coils so the thicker (read lower coils) come into play.

It does make a difference, if you install the springs thick coils uppermost you will loose a degree of the advantage of having progressive rated springs as, due to normal dynamics the upper coils which have been incorrectly installed uppermost will naturally try to compress first thus depriving you of the whole reason for having them.

[Ex Member]

Whether the coils are up or down will not affect the spring rate at all. All the coils move equally regardless. Once the closer coils touch, there are simply less coils being used in the spring and the spring rate increases. The spring rate is proportional to the number of active coils.

[Landowner]

I suppose the softer part of the spring will compress first which ever way up it is.

I only want to know which way up from the factory really as they were tight coils to the top on the Disco

I have put them tight coils to the bottom seeing as everything else on the 90 is not quite as it should be, give the rivet counters something to talk about :)

One is the front and cant see the back properly but never mind,

[Ex Member]

There is no "softer" part of the spring. All coils are the same and have the same stiffness. They all move together. The coils that are closer together run out of travel first and hit each other. Once that happens, those coils don't do anything and you simply have a shorter spring with less coils. Because it has less coils, it is stiffer. Those pictures are not showing progressive rate springs. Those are constant rate.

[Landowner]

Only the front ones are constant rate, I'll get a better picture of rears tomorrow

And I thought that it was stiffer because of the angle that the coils were to the horizontal and also the way in which it was tempered, the coils hadn't been touching when they were on the disco, there was no sigh of that at all even after heavy towing, the paint was still intact on the springs

[Landowner]

Right....

Just been out and bounced on the chassis at the back,

The tighter coils at the bottom did not move at all, the top part which has wider gaps compressed as I bounced

[Ex Member]

They all move the same amount relative to each other. It is just harder to see the bottom ones move as the top ones are moving the sum of all the coils. Trust me...I've been designing with springs for decades. The way coil springs work has been understood for a very long time.

Your photo shows a spring with even gaps.

[Landowner]

They all move the same amount relative to each other. It is just harder to see the bottom ones move as the top ones are moving the sum of all the coils. Trust me...I've been designing with springs for decades. The way coil springs work has been understood for a very long time.

Your photo shows a spring with even gaps.

Better picture of the springs.

I pulled the chassis down towards the axle today to compress the rear spring using a ratchet strap, the top half of the spring was compressing faster than the coils at the bottom, I will do it again and measure the two halves of the spring to show how much each has compressed under load when I get time.

If what you are saying is correct then when I add the body weight the coils will be almost touching at the bottom as the chassis will go down a fair few inches, that will leave me with just the top bit as a spring which would defeat the object of a progressive spring.I would be left with just the soft bit

[Landowner]

Have had a read up on springs and am now totally confused.

Progressive rate springs, they say, are softer where the coils are close together.

As the closer (softer coils) are compressed, then the wider spaced coils will come closer together and stiffen up.

So why are the close together coils soft but the wider spaced coils harder when close together ??

If the close together coils were soft then they would close together easily leaving just the wide spaced coils as a spring.

Standard springs are wide spaced and become harder when compressed

Whats the point of the close together coils if they do nothing but close together when weight is added??

I always thought that the spaced coils compressed at a faster rate than the close together ones, the close together ones acting as the harder spring.

Need input .....

[Ex Member]

The coils do not care about the spacing. The spring rate of each turn is fixed and constant. Once they touch, they are not springs anymore and do nothing.

Spring Rate = G * d^4 / N / D^3 / 8

N = number of ACTIVE coils (ones not touching each other)

G = modulus of the steel

d = coil wire diameter

D = pitch diameter of the coil spring.

Nothing in the equation has to do with length or angles of the coils. All that matters is the number of coils that are active, that can move. The coils all compress at the same time.

If you have a spring with 12 active coils and a spring rate of 240 lb/in. If 4 coils are close together, when they touch, you now have 8 active coils and the spring rate is 240 * 12 / 8 = 360 lb/in.

The coils you show above are dual rate springs (not progressive in the true sense). There are two distinct rates. One when all of the coils are free and one when the tighter spaced coils touch each other. The relative movement between each coil will be identical during compression. You would need a vernier to measure the change in spacing between the coils as they compress to see this.

Up or down does not matter. The springs are not affected by gravity and work the same way in any orientation. It does not matter which end you push from. The same thing happens.

http://www.engineersedge.com/spring_comp_calc_k.htm

[Landowner]

What I don't understand is .....

If when the nearer spaced coils are touching they do nothing, what is the point of having them?

I will have a normal spring when this happens.

If the whole spring compresses at the same rate then what is the point of having some coils closer together?

Where does the dual rate come in if the closer coils sit on each other, they might as well not be there?

The way I thought they worked was that under part load they act as softer spring but when under heavy load they act as heavy duty.

This cannot happen if the spring compresses at the same rate throughout, some part of it will have to be softer, (maybe the tighter coils) then when heavy load is introduced the tight coils sit on each other and the other (stiffer) part acts as the heavy duty bit.

Going out for a pint and to think about this, no use quoting equations to me, I don't understand the maths, just how they work in practice

[honitonhobbit]

Maybe this would explain it

A progressive spring is actually like two or three springs glued together

A soft spring glued on top of a harder spring - TD5 110 rear is 225lbs/"3 on top of a 400lbs/"3 (iirc); a TDCi110 has three weight levels...

So the soft bit - the top (as Red so decisively pointed out) acts as a comfortable cushion to the normal bumps of the road at normal load levels. Then when you have the vehicle loaded up to the gills you are running full time on the more manly bit of the spring

So they are not progressive as we would think of as truly progressive - more staged

[Ex Member]

What I don't understand is .....

If when the nearer spaced coils are touching they do nothing, what is the point of having them?

I will have a normal spring when this happens.

If the whole spring compresses at the same rate then what is the point of having some coils closer together?

At normal ride height they should not touch. They should be close. If you add a lot of weight or go hard over bumps, the higher spring rate comes into effect. The softer rate is there normally.

The problem with them is you have to have things at the correct weight "normally" so that the higher rate is only active at the right time. If your truck is too heavy or too light, they won't do what they are meant to.

My preference is a light spring with air bags inside the coils. You can adjust the height and spring rate as weight changes and they are truly progressive.

[Landowner]

Have to see when the body goes on then, Defender is about a half ton lighter than Discovery so the Disco springs may not suit. (fronts are Disco and have been great )

I am using them hopefully to stop the back end sagging when towing car trailer, time will tell

[Snagger]

A coil spring is just a torsion bar wrapped around on itself to save space. The work of compressing the spring twists the steel along the length of the bar, like a chinese burn.

The closer you pack the coils, the greater the length of the bar and the easier it is to twist (because each inch of spring is twisted less), so the softer the spring. Widely spaced coils mean less length of torque bar, so the twist and thus flex will be less. Also, the forces on an "open" coil tend to be closer tot he longitudinal axis oft he steel bar, rather than perpendicular, so more of the force is transmitted along the steel that with a "tight" coil.

I would lean towards putting the tight wraps at the bottom. Its not going to make much difference to CoG or unsprung weights, but having the softer end of the spring will mean that the upper springs will stay relatively straight for mild cross axling, with the axle pivoting at the bottom of the springs. Fit the other way up, and the axle movement will be orientated around the top of the springs, with all the undesired lateral and twisting movements that incurs and extra work for the bushes, A frame and trailing arms to keep it straight fighting eachother and the springs.

[Landowner]

A coil spring is just a torsion bar wrapped around on itself to save space. The work of compressing the spring twists the steel along the length of the bar, like a chinese burn.

The closer you pack the coils, the greater the length of the bar and the easier it is to twist (because each inch of spring is twisted less), so the softer the spring. Widely spaced coils mean less length of torque bar, so the twist and thus flex will be less. Also, the forces on an "open" coil tend to be closer tot he longitudinal axis oft he steel bar, rather than perpendicular, so more of the force is transmitted along the steel that with a "tight" coil.

I would lean towards putting the tight wraps at the bottom. Its not going to make much difference to CoG or unsprung weights, but having the softer end of the spring will mean that the upper springs will stay relatively straight for mild cross axling, with the axle pivoting at the bottom of the springs. Fit the other way up, and the axle movement will be orientated around the top of the springs, with all the undesired lateral and twisting movements that incurs and extra work for the bushes, A frame and trailing arms to keep it straight fighting eachother and the springs.

Very technical, thank you

If I were wanting axle articulation I would go for the softest standard springs I could get, the ones I have are for towing with a lot of weight on the towbar.

getting very informative this thread so thanks to everyone for that

Pete