Spring stretch ... ?

[Anderzander]

My X-Springs need new springs and plates - but I'm struggling to get the replacement parts from Foundry. So I've been thinking of what my alternatives might be.....

And it's either dislocation or spring retention (where I can't afford coil overs) .... So my question is can I calculate how much a retained spring will stretch ?

The spring calculator does static sag - so I guess I could play with that on negative values ? But of course under dynamic movement the springs compress a great deal more - so will presumably stretch a great deal more too ...

Anyone able to help educate me please ?

[bill van snorkle]

I understood that a non dual rate spring has the same rate in tension as it does in compression.

[elbekko]

Statically you should be able to work it out based on unsprung weight (axle weight).

Apart from that... a forklift and a tape measure?

[discomikey]

could you not contaxt Si directly?

i am of course assuming you mean X-eng X springs. in which case being the owner of the business he would be more able to sort you out than your supplier.

p.s. if you are planning on doing much off road, retaining the spring both ends will result in a fair bit less articulation as when past its natural state the spring will be pulling the axle back up again off the ground.

[Anderzander]

I think Si has handed sole distribution over to Foundry so he doesn't have to deal with sales and queries - so I've nowhere else to go.

I know what you are saying about less articulation - but I'm not sure how much less ?

I'm thinking the dynamic loads, the compression of the opposite spring, and the weight of the axle and wheel will variously provide leverage and weight to stretch the spring out ?

So I don't know how deep the restriction will be ? I think I'd rather some restriction than go the dislocation route.

[discomikey]

what shocks do you currently have?

i know you like to lane so i guess it depends on how much they currently limit you to as to wether it will make a difference.

[Bowie69]

Send him a PM on here, I'm sure Si would help.

[Anderzander]

OME +5's. There's a fair bit of travel on them - so I'm certain the springs would be the limiting factor. Just not sure how much ....

I don't mind losing some. At the moment I'm on some temporary retainers I made up for the bottom when I took the x-springs out. Perhaps what I could do is put some jubilee clips on the top and try it out. If it works out then I can get some of Gwyn's chunky spring retainers....

[discomikey]

yeah that sounds like a plan although im sure that Si will be able to sort you out even if he doesent handle stock usually. he will probably have test springs lying about etc?

p.s. maybe he would be interested in the details of why you need to replace them as it may provide some ideas for his product development. you never know.

[bill van snorkle]

See post below. I don't know what I did wrong!

[bill van snorkle]

If the Gods of engineering at LandRover knew that retained springs were a good idea, they would have retained them at the design stage.

Anyway, I would think it is reasonably easy to calculate how much weight the wheel on the drooped side still has, once the spring dislocates by looking at the axle assembly as a see saw with offcentre pivot points (centre of spring saddles). Someone clever is welcome to correct me, but here is a rough example based on the following values of rear vehicle weight, track width, and spring spacing. Track width =5ft. spring spacing = 3ft. see saw lever arm ratio = 1:4. Rear end weight = 2000 lbs. When the full weight of rear end is focussed on a single spring during articulation,,providing the compressed spring isn't coil bound, the 1:4 see saw ratio transfers 25% of that 2000lbs to the drooped wheel, so at the point of dislocation the wheel on the drooped side is still carrying 500lbs.For retained springs, if your coil spring rate is 250lbin then the drooped wheel can drop a further 2'' before it no longer has any traction.

Of course there are other variables that may come into play to either reduce or increase articulation, such as tyres fouling on body/chassis, or tyre pressures and diameter etc.

After that mental exercise I can see a small case for mounting the coil springs on pivoting saddles at the axle, so when the spring is coil bound, the see saw pivot point doesn't move out closer to the wheel and reduce the lever arm effect.

Note. the values and dimensions above don't necessarily apply to any Landrover. It's raining and I can't be arsed going out to take accurate measurements.

[Anderzander]

Bill - no need for getting wet, that is enlightening for an uneducated / inexperienced fellow like myself. Thank you !

I also wondered how a compression spring would cope with being stretched - but it seems that providing its not overstretched, which of course it wouldn't be, then it should be fine.

Mine has 1914 lbs on the rear, which I estimate to mean around 1500 lbs un-spung weight. I've also 'progressive' springs of 155 to 215lbs. Not an easy calculation there I think - though they may in fact be dual rate springs rather than a genuine progressive one ... either way - your maths is enough to point out that we are talking about a small number of inches.

[bill van snorkle]

I've heard it said that a coil spring is just a torsion bar made into a more convenient shape. So compression twists the torsion bar in one direction, and tension twists it in the opposite direction, so I would imagine that a spring say 17" long and capable of being compressed to 11" long, would also be capable of being stretched to 23" before the elastic limit is exceeded.

As I re read some of my first post I'm beginning to see how stiffer/stronger springs may not necessarily affect articulation, because they are less likely to become coilbound, and therefore the pivot point remains centred rather than moving 3" closer to the wheel.

These are small amounts as you say Stephen, but when chasing the limits of capability, every little bit can mean the difference between driving a section or dragging out the winch rope.