I'm a designer/tweaker by nature, and by no stretch of the imagination am I a skilled fabricator. Consequently I wanted to throw this idea out there for a while now and see what folks think. Posted it to the Snort4x4 board but hoping to get some wider input here too.

I’ve spent a fair amount of time on understanding the basic advantages and disadvantages of coilovers vs. leaf springs.

Basically coilovers generally allow more travel, are easier to adjust ride height without changing spring rates, allow for easy and simple spring rate changing when needed, allow for fairly simple dampening modifications and are typically rebuildable. Since they use coils they also have minimal integral spring friction (no leaves to rub against each other) and tend not to sag as much over time if you get good coils. More importantly from a fabrication and articulation standpoint they are pretty tolerant of somewhat inaccurate placement (at least to a point) as the coils don’t have any extra resistance in particular planes of movement as they are after all, coils, and there are only 2 mounting points rather than 3 on leaf springs.

But the biggest drawback I can personally see is that they have very little resistance to unloading as the coil springs themselves are not truly captive; the coils just sit loosely on the shock body unless loaded. The spring seat design also means you typically have to have enough spring extension to extend at least as much as the shock body itself (or as much as any limiting strap allows it to extend) to keep the lower spring cup from getting misaligned, rattling around or even dropping off, at least on designs like the King Technologies shocks and several popular others I hear. So any resistance to suspension unloading is strictly due to the internal dampening and that is only as a function of time and movement (zero resistance unless the shaft is in movement) and the resistance to unloading via this dampening is actually decreased in effectiveness by the need for the follower coils needed to keep the lower spring cup retained (they are trying to extend the shock.)

The key point I am trying to make here is that there is no tendency to "return to center" like a leaf spring.

Leaf springs, quarter elips, etc. when used with conventional mounting points have the advantage of having a static rest point that offers resistance in both directions: they offer resistance to both compression and extension. That effect is even more pronounced and well balanced if you are running springs and or mount configurations that allow you to use a fairly flat spring. This helps keep the suspension from overly unloading. The point here is that this "return to center" has a distinctly predictable and progressive tendency to return to center (progressive in that depending on how far the axle is from the rig, the force pulling the axle and rig back towards each other is progressively greater.)

That return-to-center effect coupled with the increasing trend to build lighter and lighter rigs and use heavier and stronger axles should generally result in pulling the rig back towards the axle rather than vice-versa, which in turn keeps your center-of-gravity down when going uphill, downhill or sidehill steeply, thus reducing the chance of a roll over.

With coilovers since they want to unload to full extension by design, to keep you COG down you end up needing to run limiting straps so that the suspension doesn't overly unload, your COG get too high and then you get into a roll over. Also because there’s no tendency to return to center it seems reasonable that you need to essentially overly limit the suspension so as to keep the rig from gaining negative momentum as it relates to COG: namely again because the coilovers by design want to unload and there is likely to be an increasing velocity of the rig away from the axle, which you want to arrest as early as reasonably possible. So the problem as I see it is for coil-over rigs is that you often end up running limiting straps that hold the suspension back a bit more than you’d really like to arrest that momentum before it occurs. Also there's the very distant secondary issue that with current limiting strap designs under rapid extension (especially with light shock valving and/or smaller diameter shocks on a heavy rig) there’s a fair amount of jolt to the frame and mounts/link bars/whatever when the limiting strap becomes taught too quickly.

So the question (finally, I know): has anyone ever thought about or ran across a limiting strap that has a substantial and progressive amount of stretch? What I am thinking is say something that would stretch for possible 4 - 6 inches at a rate of say 150 pounds/inch. Then the suspension really could even be arrested by a second seperate strap, wouldn't have to complicate finding a material by needing something with more complicated characteristics (i.e. stretching for distance X at Y pounds/inch force for a distance of Z at which point the stretch stops altogether.)

Anyway, that's why I am having a difficult time - locating a material like that. I'd like to find something with say 150 pounds/inch stretch for say 5 inches for example that would be resistant to a change the material characteristics under repeated use.

I'm all ears if someone knows of a source for materials that might fill the bill or any leads on where to start!

Seems like there could even be a smaller but reasonable market for custom order straps (just like folks order custom springs) that allow you to choose custom lengths of stretch and particular stretch “spring rates”.

Thoughts?

Bungee cord. :)

J. J.

"I'm a designer/tweaker by nature"
I heard that :rolleyes:

Run a swaybar and walla your done!!!!

Or you can take the idea of a sway bar and incorborate it into your limiting strap, have the limiting strap tight at ride hight and the end attached to a lever off a torsion bar or to the end of a short leaf spring. torsion bar setup would be more compact and lighter also would be progressive and easy to adjust by changing the length of the lever and length of strap

You could do it like how they have bungees for bungee jumping and have a bungee with a limit strap zip tied to it every couple inches with extra slac in each segment of strap to allow the bungee to stretch.

Or another idea is to have a device that houses a small spring with the desired rate, and the bottom of the spring would be conected to the frame and the top of the spring conected to the axle so that when the suspention un loaded it would compress the small sring creating the droop resistance. I can picure this one in my head and it would work good i thind but i can't explain it well but i hope that makes sence.

Good topic, i too have thought about this, when designing 1/4 elliptic setups and thinking it would be cool to have a coulpe of leafs under the main leaf to create droop resistance, as well and having the typical pack obove.

Ian-

Originally posted by NE-RokToy
Run a swaybar and walla your done!!!!

Or you can take the idea of a sway bar and incorborate it into your limiting strap, have the limiting strap tight at ride hight and the end attached to a lever off a torsion bar or to the end of a short leaf spring. torsion bar setup would be more compact and lighter also would be progressive and easy to adjust by changing the length of the lever and length of strap

I likes that idea, SIMPLE.
But sometimes doing something different can be fun and you may run across something that works better.

Ian-

You need some of those rubber band things from a SOLOFLEX;)

Originally posted by Scout Dude
You need some of those rubber band things from a SOLOFLEX;)

:laughing: Soloflex hahaha, you have seen way too many infomersials.

Ian-

Originally posted by KrustyKruiser


Or another idea is to have a device that houses a small spring with the desired rate, and the bottom of the spring would be conected to the frame and the top of the spring conected to the axle so that when the suspention un loaded it would compress the small sring creating the droop resistance. I can picure this one in my head and it would work good i thind but i can't explain it well but i hope that makes sence.

Ian-

Something like this?
http://www.safarigard.com/Droopkit1.gif

That is kind of what i was thinking of using, but in that picture that spring seems to be a bump stop or something. Also since we are talking about coil overs it could not be an internal piece, but that is a good pic to get some thoughts started.

Ian-

Originally posted by KrustyKruiser
Or another idea is to have a device that houses a small spring with the desired rate, and the bottom of the spring would be conected to the frame and the top of the spring conected to the axle so that when the suspention un loaded it would compress the small sring creating the droop resistance. I can picure this one in my head and it would work good i thind but i can't explain it well but i hope that makes sence.

look here-

http://www.safarigard.com/Droopkit.htm

adam

That looks like an added droop feature to me, also in that desiegn the small spring only gets compressed when the coil reaches full hight, what we are looking for is something that ads resestance even beforethe spring completely unloads, so that it could ad resistance at the very begining of the droop cycle.

Ian-

I will somday try my two way air bag that will have one to carry the load, and one on top to push or pull the other way to add compresion. What this will do, is alow you to raise the hight on the trail by running high psi on the bottom and low on top then when back on the highway, you can run high presure on top and just enough on the botom to get it off the bumpstops (about 2") and the rate will be high to have good control on the road. The problem with running just the botom bag as traditional is that if you try to lower it on road, you also lower the rate making it ride like a boat.

How about a hybrid suggestion I've made before (regarding something I've thought would be cool to try some day). Use a quarter elliptic setup front and rear that normally ride on bump stops like most QEs do. However, beside the bumps would be a second bump that rides on an air bag. You could inflate the air bag to raise your ride height for break-over or whatever you need, and lower for street, off camber, etc. to have the relatively higher rate of the leaf packs. Added bene is that if you blew a line/bag, you still got suspension that works just fine, all you loose is the adjustability.

Now, starting from that, it’s not too big a jump to limit the down travel so that the leafs are responsible for soaking up excessive droop. Easiest would be a manually adjustable limit strap affair located out board (opposite the anchor relative to the bump(s)). Only problem is you would need to “manually” adjust it in order to let the bags work for significant lift. Never really thought about that angle before. Hmmmm…