Shortening a Car Coil Spring

[Nomad]

Reducing the maximum extension will not change the static height. That is governed by the spring alone (unless you have air shocks, not the case here).
Restricting extension is nothing to do with the problem.

Very true - I restricted extension when I fitted shorter springs but it was done to stop the springs becoming loose at full extension (and possibly jumping off the spring seats)

Reducing static height is the first challenge, only then can you tell if you also need to restrict full extension to keep the springs in place.

 

[Kram]

Stick a G clamp on the spring, no need to cut it

 

[Screwdriver]

Reducing the maximum extension will not change the static height. That is governed by the spring alone (unless you have air shocks, not the case here).
Restricting extension is nothing to do with the problem.

Very true - I restricted extension when I fitted shorter springs but it was done to stop the springs becoming loose at full extension (and possibly jumping off the spring seats)

Reducing static height is the first challenge, only then can you tell if you also need to restrict full extension to keep the springs in place.

Then you must be using the word "extension" differently to me. I only used the word to respond to @Morris who said you couldn't "pull down" the suspension mechanism to change the ride height without "restricting extension".

Now I am being deliberately vague in my description (e.g. pull down, mechanical stop) because the OP has not defined the precise mechanism by which this suspension system operates. Far as I know it could be coilover, leaf spring, air bags, wishbone, dog bone or whatever. Doesn't matter. There MUST BE some mechanism which stops the suspension system from falling apart if the wheel leaves the ground.

I am using "extension" in the vernacular here because when the suspension extends to it's maximum extent there has to be some sort of stop to prevent it from extending too far and falling off! If on the other hand if there is some sort of secret meaning to the word "extension" that suspension gurus use at their Masonic lodge then please explain why reducing maximum "extension" does not change ride height...


PS I am having some sort of "moment" this morning and find myself in extremely good spirits as if a fog has lifted so please accept my apologies if I am coming across as combative. I am enjoying this conversation and rather hoping I will learn something from it!

 

[Morris]

Forget the extension! At it's core it's a mass on a spring. The spring compresses until equilibrium is achieved. That is the ride height. To change it you can shorten the spring or change the spring rate eg softer or stiffer. Indy4x wishes to lower the point at which equilibrium is achieved. Changing the spring rate would affect the ride (which we must assume he is happy with) so the alternative is to reduce the spring height. The extension/compression is part of the dynamic characteristics of the suspension, we are only dealing with the static conditions re ride height.
Extension is a consideration with 4x4's as it is what keeps the wheels in contact with the ground and therefore maintains traction.
Extension

Compression

 

[Morris]

Addition to above post
@Screwdriver it says coil springs in the OP.

 

[Smallfry]

How many bags of sand or cement would it take to lower by 55mm ?

When you need load levelling facility, you can take some out. Ta ra .........

No MOT or insurance problems, no cutting or bespoke springs needed, and no risk of displaced springs.

I should send this to "Viz" to tips

 

[Screwdriver]

Forget the extension! At it's core it's a mass on a spring. The spring compresses until equilibrium is achieved. That is the ride height.

Doh! Of course I should have seen that. You're right of course. I somehow forgot the vehicle doesn't sit at the maximum available extension.

 

[hotponyshoes]

That spring has smaller diameter coil(s?) on at least one end so it's not a linear rate spring.
If you restrict the extension you'll pre-load the spring over the softer part so it will give a harsher ride.

On the other hand, if you chop it in the location shown in the photo you'll maintain ride quality but might bottom out /bind it up over bumps/heavy loads.
If you cut it check the bumpstops come into play before the coils bind.

 

[Gareth J]

The engineer/metallurgist in me can't help think that chopping a spring is going to alter the spring characteristics and potentially introduced stress concentrations. Heating, bending and heat treating it is going to risk unknown new temper.

I know it's not a race car but none of the above are good things to have in anything, let alone suspension components.

A less sketchy solution, if possible, might be to raise the top mount. Or scour parts for a close match in terms of vehicle weight and desired suspension characteristics and use shorter springs from that. But that's a bit of a difficult thing to do!

 

[hotponyshoes]

If you are not in a rush you could get some custom springs made up.
I've used a place before, you just send them the spring and tell them what you want changed and they send you some new ones that just work.
Not particularly expensive either..

 

[octo0072000]

that alloy block does not seem factory fit have you checked with jeep if it's standard or not that could be your 55mm if it 's lower

 

[Blobber]

Seems a lot to cut off, I reckon it will drop more than 55mm if you cut that much off