Dual spring rate K5....Coilovers and Torsion Bars???

[Greg72]

The discussion we had about airbags and coilovers didn't really seem to bear fruit....I'm with you guys who responded, it's not likely to be an elegant (or simple) solution......and when it comes to 4x4 building, complex is NOT the correct direction to be headed!!!

As I thought about it, the concept of adding torsion bars with a "disconnect" on the torsion "arms" might be a lot simpler and more elegant. Imagine that the torsion bars are installed laterally underneath the frame and "in-line" with the suspension links on the frame end. (In my mind I'm envisioning a converged "V" 4-link with parallel "uppers") Those upper links are basically parallel to the ground and would make a nice place to attach a torsion arm and a disconnect system.

The theory is that the torsion bar could be fairly small in diameter (or I could use a long torsion arm to soften the rate)...this setup in tandem with the coilovers would provide the stiffer "street" rate....and then by pulling the disconnect pins/bolts, the torsion bars would effectively be removed from the equation to get the softer "offroad" rate.

What I like about this idea is that the setup could be quite simple, and the disconnects would be easy to reach from each side when you get to the trailhead.


....anyway, it's something I've been mulling over for the last couple of weeks, so I thought I'd throw it out for discussion or rebuttal. I can post a sketch of what I'm talking about if the description above is not clear.

 

[6.2Blazer]

I'm not seeing how this would work. Torsion bars need to "twist", or rotate, to provide any spring rate. Therefore I would think the only way to make a torsion bar with a solid axle would some sort of complicated linkage system that converts the linear "up and down" motion of a solid axle suspension into a rotational movement.

 

[Greg72]

See if this helps...... thanks MS Paint!

In reality, the torsion bar wouldn't be above the upper horizontal link (as pictured in side profile), it would have to be in exact alignment with the link pivot to prevent binding. The end with the "disconnect" on it would need to have some sort of heim end on it to allow it to twist with the articulating link arm.

Make any more sense???

 

[ntsqd]

One of the downsides to the Early Bronco hinged, or "Wristed" Radius arms is that they are a pain to lock for pavement driving. Most use a second pin to lock out the hinge. Alignment of the two holes is almost always problematic. See where I'm going with this?

For the system to be relatively painless to lock or unlock you will need something that forces the alignment so that the pin(s) can drop in. If you have OBA that could be as simple as a double acting air cylinder(s) and a control valve to force the anchor to line up so that the pin(s) can be inserted. The valve would need to be an open center type so that the anchor(s) could rotate w/o compressing air while 'unlocked'.

No matter what you do, in some mode of operation you are going to have compromise shock valving.

 

[bgreen]

To help the alignment problem, just drill a second set of holes that you can use to stab a pry bar, or alignment bar into.

 

[6.2Blazer]

Okay, understand your design now. It still looks like it would be pretty complicated to implement by the time you fabricated the torsion bar mounts (solid mount on one end, and some sort of bearing it could ride on at the other end).

What is your reasoning for wanting higher spring rates for road driving? Is it just to control body roll.......if so, wouldn't a really big quick-disconnect swaybar do the trick.

 

[Greg72]

Okay, understand your design now. It still looks like it would be pretty complicated to implement by the time you fabricated the torsion bar mounts (solid mount on one end, and some sort of bearing it could ride on at the other end).

What is your reasoning for wanting higher spring rates for road driving? Is it just to control body roll.......if so, wouldn't a really big quick-disconnect swaybar do the trick.

A swaybar could solve the problem for body roll, but the squatting and pitching during acceleration and braking gets annoying too.....something that a swaybar can't address.

I'm sure the switch to a high-quality coilover will be a dramatic improvement over my current setup, but I'd like to be able to mess with really soft spring rates on the coilovers and then have the ability to play with the torsion bars as a way to substantially stiffen up all aspects of the ride for street driving.

Now that I think about it, having a torsion arm with multiple mounting holes for the disconnect means that I can have design a decent range of effective "extra" spring rates. I'll have to spend some time with the calcs to see how to optimize that. Swapping out torsion bars for thicker or thinner ones to adjust the rate is nowhere NEAR as easy as moving the attachment point around on the torsion arm!!!

 

[6.2Blazer]

It will be interesting to see what you come up with. However, my gut feeling tells me that if the spring rate is so soft that braking and accelerating on the street cause problems, then you will also have problems on the trail........sounds like it would be very interesting climbing or descending hills with that much body pitch forward and back.

 

[ntsqd]

Keeps coming back to position sensitive damper valving i.e by-pass dampers. Soft thru the middle, progressively stiffer at each end. Fox does internal by-passes that may take c/o springs, can't recall.

 

[Stephen]

I think a lot of your pitch/roll problems will go away if you stick with a low CG height and stiffen up the springs just a little by going with triple rates on the C/O springs.

That and a small swaybar might just do it for you and not require messing with on and offroad suspension settings.

 

[surpip]

Swapping out torsion bars for thicker or thinner ones to adjust the rate is nowhere NEAR as easy as moving the attachment point around on the torsion arm!!!

Actually it isent as had as you might think, mabye a little more expinsive, but sprint cars Use this same set up, they use little torsion bars, and switch them out depending on the track, I cant really describe it very well but if you can find a sprint car to look at youll see what im talkin about

 

[BAJA_BLAZER]

Greg, I went back and read your original post about using Air Bags and the read through this thread and am a little confused as to what you are trying to accomplish.



“I have been mulling over the idea of building a softly-sprung vehicle (kind of like I already have!) maybe something with around 250Lb-in springs for offroad use....then use an airbag setup to increase the spring rate for street driving...up to maybe 500Lb-in (or whatever I choose)”



If I understand you correctly; you want your suspension to be soft (compliant) when off road. By off road I assume you mean low speed “wheeling” and Rock Crawling, because you do not want your suspension too soft for high-speed offroading, as it will constantly bottom and have very poor handling characteristics. And, you would like to be able to stiffen the suspension when driven on the street. You talk about adding spring rate dynamically by using an air bag or torsion bar to accomplish your objective, but don’t want to add ride height. Restated, these are your objectives:

• Soft flexible ride off road when rock crawling.
• Firm stable ride on road and in high speed off road driving.
• Maintain same ride height in either mode.

Now I’m no engineer, but I have been setting up suspensions and rebuilding and tuning shocks for years, so here is my 2 cents worth of knowledge.



The primary purpose of a spring is to carry or support the sprung weight of the vehicle. If you place 1000 lbs of force on a 250 lb constant rate spring (meaning the spring’s rate is 250lbs per inch of deflection) it will deflect 4 inches. If you add a secondary spring in the form of an air bag or torsion bar attached between the load and the unsprung weight, it will add spring rate and raise the ride height.



Spring rate is the amount of weight needed to compress a spring one inch. If you increase the spring rate at all it will raise the ride height if everything else is kept constant. You could maintain the same ride height with a shorter (flatter in the case of leaf) spring with a higher spring rate, but that would not be what you are after. The only reason for increasing the spring rate in your case would be for higher load carrying capacity, which you did not state as an objective.



What I am confused about is your desire to change the spring rate to accomplish your goals. I’d suggest that you change your mind set away from spring rates and added springs (air bags, torsion bars) to ride control and damping, a function of the dampers (shocks).



Typically a high quality rebuildable mono-tube shock has both low speed and high speed damping adjustability. Low speed and high speed refer to the shaft speed of the shock not the speed of the vehicle. Examples of low speed dampening would occur over gradual undulations in the road, body roll around a corner, and rock crawling. Examples of high speed damping would occur while driving over washboard roads, landing from a jump, hitting a bump in the road.



In rock crawling you want very little low speed damping, and mostly rebound, only slightly more than necessary to control the osculation of the springs and weight transfer. High speed damping rarely comes in to play in rock crawling.



Ironically the firmer control that you are seeking on the road is also primarily a function of low speed damping. The difference is that you want greater low speed control to eliminate that wallowy mushy feeling. Firmer low speed control can help to eliminate body roll, and weight transfer.



One way to accomplish your goals is to use a reservoired shock with an adjustable flow restrictor between the shock and the reservoir. When a shock is compressed, the shaft travels into the shock displacing shock fluid, equal to the volume of the shaft, into the reservoir. When the shaft is withdrawn, the same volume of fluid is returned from the reservoir to the shock body. As a side note, this exchange of shock fluid between the shock body and the reservoir aids in cooling the shock. Restricting the flow of fluid between the shock body and reservoir will “stiffen” the damping characteristics of the shock in both compression and rebound. Some manufactures may still offer the “Clicker” style reservoirs that allow you to adjust the flow. There are also various ball valves and flow restrictors available that would work for you.



Another possibility is to use a bypass tube. Without getting into a lot of detail, an open bypass tube has more impact on low speed damping than it does on high speed damping. In a low shaft speed situations the bypass could be open, allowing the shock fluid to go around (bypass) the valve stack. Closing off the bypass would force the valve stack to come in to play, increasing the low speed damping characteristics of the shock. Off the shelf bypass shocks would give you the adjustability that you desire and provide progressivity with multiple tubes.

 

[Greg72]

Ramsey,


WOW! After a detailed response like that, I feel compelled to respond with as much information as I can...


I will admit to never having ridden in a well setup coil-sprung rig, and that may in part, explain things. My experiences are based on a relatively small sample of leafsprung trucks and a few short years invested thus far in this hobby.

When I first bought my K5, it rode on some Rough Country 4" lift springs. They were something like 700 Lb/in springs up front and you can imagine the ride "quality" . Once I realized that the springs were at fault (I was very green at this point) I had Stephen at ORD make me up a set of custom 9-leaf springpacks that were rated at 237 Lb/in. Talk about a dramatic difference in ride quality!!! Along with that came some undesireable street manners....namely the pitching and bucking and a LOT of bodyroll in corners. Enough in fact, that my fellow K5 brothers were terrified to watch and follow me on the twisty access roads to Hollister or Frank Raines!!!!

I played around with shocks briefly....my entire experience thus far has only been with the Rancho 9000s. I could add a few clicks for street driving and get a modest improvement, but bodyroll is still bodyroll.....albeit s-l-o-w-e-r body roll with a stiffer shock setting. BTW -> I recently came into possession of a set of Bilstein 7100 resevoir shocks (for cheap!) and was looking forward to swapping them into the existing setup to give myself some extra insights into what role shocks (especially a quality shock, since I don't feel the Rancho really is!) play in improving the street handling of my K5.

(FOOTNOTE: If you happen to know how to re-valve shocks like the 7100 and are willing to share that info, we have LOTS to discuss! )

The idea for a dual-rate K5 came from many discussions on CK5 where people lamented the loss of streetability when converting their truck to serious rockcrawling capability. Clearly it seemed, the behaviors for those two functions were on opposite ends of the handling spectrum and no SINGLE setup could be expected to do both WELL..... ?

As most of the old-timers here know, I'm a stubborn bastard when someone tells me something isn't possible....to me, that simply means that the problem needs more thinking, and/or more money and resources than anyone has been willing to invest. I reasoned that there HAD to be a way to setup a secondary set of springs to stiffen the truck....airbags were an interesting choice, but as you already noted....adding air, not only adds "rate" but also "height"....and more height was not what I wanted. The torsion bar idea came about as a way to add "rate" without adding height.... I envisioned the torsion bar as having no preload at static ride height (that is 0 lb/in) so conceivably there is nothing additional pushing the vehicle upwards....the primary springs (in my case I'm expecting this to be King Coilovers) are holding the sprung weight of the truck, and would be rated somewhere in the 250 Lb/in area. The idea of the "disconnect" is to allow the truck to run only on the Kings for offroad use, and only when on-road would I "couple" the torsion rate to the coilovers.

Now at this point, you may very well be saying..."this guy really just needs to experience a good quality shock setup..." and in fact you might be right. The only reason for all these up-front strategies is that I'm embarking on a new "from scratch" buildup of a '69 Blazer, and at this point I'm looking at a clean sheet of paper......if there are considerations to be incorporated, THIS is the time to identify them. Adding torsion bar mounts to the design now is easy. Retrofitting them later will be a LOT more work. I'm really just trying to explore all of the available options beforehand so that I don't design myself into a corner.


.

 

[BBchevyMAN]

Spring Rate

As far as I know you should have a soft spring rate and control the truck with the shock valving. On the front of my truck I have a tender spring on top with 12" 200lb ontop of a 16" 350lb, on a 16" travel racerunner coilover. On the rear I have a 50lb tender on top, them a 150lb 14" then a 200lb 16". Also 4" travel 2" King hyd bumps all around.

 

[sreidmx]

Sounds like you are a prime candidate for a shock with a flutter stack to control your lower speed damping, then blows off on the higher speed hits(speed is relative to shaft velocity). You can have really soft springs that flex well at low speeds but you need to back them up with bumps and quality shocks.

There are two schools of thought to accomplish the same thing.
Soft springs heavy valving
stiff springs light valving.

This is realitive of course, progression plays a huge part which is why leaf springs are kinda nice because you can build much more stiffness later in the stroke kinda like a coilover.

7100s are not hard to rebuild at all, this valving isnt that complicated especially if you are making small changes to understand how they affect the chassis. If I were you buy a pair and the tools to revalve them and try it based on bilsteins valving charts, they quantify damping force in Neutonmeters so the 360/80 is 3600 neutonmeters of compression damping force and 800 for the rebound.

Do some more research, you have the right springs for what your doing.

 

[sreidmx]

Oh and dont over think it. you will feel if you are getting close or not.
You mainly need to understand the basics of the types of bumps your trying to tune out. video helps a ton.

 

[Greg72]

Oh and dont over think it. you will feel if you are getting close or not.
You mainly need to understand the basics of the types of bumps your trying to tune out. video helps a ton.

Thanks for the reply (and the trip down memory lane!)

I'm not sure if you noticed, but that thread is 8 years old! I gave up on that idea a long time ago.... You can see more recent stuff by following the build thread link in my sig.

By the way, if you know about tuning ORIs (struts) feel free to jump in!


-G

 

[sreidmx]

HAHAHAHA damn I didnt even see the date...ROFL.