How do you interpret spring rates?

[PeeBee]

I am curious to understand how the definitions of springs on the market are defined. For example when I purchased my 1997GQ Patrol, new, I upgraded the very soft factory suspension to ARB 'Medium to GVM' coils. These turned out to be fine around town with a young family and no load in the vehicle.
The first time we went away with all the 'stuff' the vehicle sagged in the rear. I returned to ARB and was advised to install the 200kg 'constant rate coils', which were firmer and carried the load reasonably well, however over time, after adding more 'stuff', these were upgraded to 400kg 'constant rate coils' - not ARB.( which I sort of regret)
I thought I had sorted out my suspension for my needs, and the vehicle articulated well and drove beautifully, bearing in mind the front coils are still the original ARB Med-GVM springs.
A stint in the QLD mines on FIFO put an effective end to any trips of consequence for 4 yrs. During this time the vehicle sat in the garage, and the rear end dropped within a year and I was back with the 'nose up stance'. ( I did go back to the supplier of the coils and was told ' tuff luck, thats what happens when you abuse a spring???//) I added air bags and this is the current config, however quickly followed by coil tower strengthening and cross tower linking as the stress has to go somewhere. I am now in the process of planning to remove the airbags from within the coils and replace then with the style that works between the axle housing and chassis as I believe the tower stress will reduce.
My vehicle is getting an engine transplant in WA and also a GVM upgrade. I would like to have some say in what the front & rear spring solution should be, however the industry marketing does not seem to give me an understanding of what 'style' of spring I should be leaning towards, or what their desriptions will deliver.
My driving these days is limited, Victorian high country stuff mainly and nothing axle busting. The longer haul trips are the goal.
I understand the issue that the springs sag because of the weight, and I am now on a path to cutting back on the excessive crap i think I have to haul around each trip, so the vehicle mass will come down.
Can I get some explanation on the various styles , such as variable rate, constant rate, flexy etc, specifically with regards to spring rate itself and how it is determined. From my engineering design days we specified spring rate in n/mm deflection and then worked with a box of sample springs supplied from a manufacturer to try and match the effect you needed - this is machinery design, not automotive. The process started out 'all technical' however basically that was just the starting point. I guess its hard to understand what 400kg constant rate really means from a user perspective, or should i be trying to find some sort of progressive rate spring that firms up with deflection, and how do you specify that to a manufacturer/supplier/vendor? I don't tow a trailer but intend to in the future, along the lines of a Tvan or similar.
Apologies for the long intro, just trying to hone in specifically on the subject area.
Thanks guys, Phil.

[threedogs]

You should weigh your axles front and rear, armed with that go to an 4x4 shop
with that knowledge and accessories fitted like dual battery, bull bar and winch
The drivers side is slightly longer to compensate for the driver, different spring mobs
may have a different formula to work out whats required. you may need 150lbs in the front
and 200lbs in the rear.
You would need to communicate with the vendor what your intended use would be.
They are pretty good these days matching up coil springs @the evil twin would know

[BigRAWesty]

Unfortunately you'll have no input with the gear used with the gmv upgrade.
But imo if your not running fully loaded all the time it's going to be rough as guts..
(Personally experience)
We've now gone a coil which suits it's daily setup and kevlar to assist when needed.. we have the 3.5t gvm.

[threedogs]

Unfortunately you'll have no input with the gear used with the gmv upgrade.
But imo if your not running fully loaded all the time it's going to be rough as guts..
(Personally experience)
We've now gone a coil which suits it's daily setup and kevlar to assist when needed.. we have the 3.5t gvm.

I think he's getting a 6.5td implant shortly, at brunswick diesel

[PeeBee]

I think he's getting a 6.5td implant shortly, at brunswick diesel

Thanks Guys,
currently have 400kg rears with airbag assist. The ride is fine because of the load, but I need the airbags to level it up. I will wait and see what Brunswick come back with after the upgrade. How does the 'engine doing the ugrade' quantify the actual increase? Is it a combination of springs and brakes and the type of tow hitch fitted? Putting it simply, I can't see them going higher rated than what I am running now - not sure if anything is avail.

[PeeBee]

'engineer doing the upgrade'

[GeeYou8]

From what I understand, 4x4 springs are rated at how many extra kg you can add to get back to original (standard or raised) height, as opposed to race car springs which are rated in pounds which appears to be the actual spring rate.
Even if overloaded, springs should not sag, they are called springs because they spring back.
Graham

[BigRAWesty]

From what I understand, 4x4 springs are rated at how many extra kg you can add to get back to original (standard or raised) height, as opposed to race car springs which are rated in pounds which appears to be the actual spring rate.
Even if overloaded, springs should not sag, they are called springs because they spring back.
Graham

All springs are still rated in weight capacity.
The whole +xxx kg is a lazy scale.
Any good suspension supplier will get actually weights, not a list of accessories.
Although the list of bolt on's will get you close enough it's still very rough..