Here is the post I was working on dumping all the various info I found as I went. I know some of this will be a repeat of info I already posted but I do not want to have to go thru all of this again and I doubt it hurts anything.
My main goal thru all of this has been to learn given I was pretty much sold on the dual ladder bars before all of this. Obviously I needed to learn a lot more.
What I have found in doing some basic CAD stuff and working out geometrically as well as spending hours and hours over on pirate4x4 and dezert racing forums the last week researching nothing but traction bars:
(I may or may not get some of this wrong and I am not certainly in now way stating that what I post is in any way definitive. It is only what I have or think I have come to understand about the workings of the traction bars etc.. The best thing that can come from this is it generating questions possibly debate and best of all ideas possible completely new or old proven technical understanding. )
If you desire to run bars on each side of the axle and want reasonable amounts of articulation with travel then you MUST only run a 2 link system. This is how the OUO is made. The real issue is that when you do not use a shackle mount that allows for the leafs travel it will cause travel binding of the spring but it can get close and the bushing does take some of the bind. You can get very close but there will be some binding. Now the fact is the leafs are flexible themselves. Just look at what they do when you run thru some obstacles etc. So being strong enough the bars can force the area of bind into the leafs and make them flex to allow for it.
This is not ideal but it does work and does allow for in general the easiest install and symmetrical look to the system. That is why the OUO is so popular. They add welding gusset to help limit the weakness of single bar setups which is bar flex. The post frame mount with bushing allow for 360 degrees of limited travel. Also being so long it minimizes binding thru the travel range and articulation. The one issue with this system is to get maximum performance the axle mount point needs to be below the axle and the farther below the better the bars performance. This does create lower ground clearance and a place to get hung up or slam into objects. No way of getting around this other than to make it so things slide over in in the forward direction but its still a clearance reduction. But again this is something obviously many can live with as most are not seriously off roading these full size rigs but some are.
Now if you want absolutely no bind in even some of the very extreme travel and articulation of the leafs and rear axle and also want the utmost in control over wrap as well as being able to actually have some control over antisquat of the rear end you need to look at a 3 point A frame traction bar. Notice I said bar not bars. You need the traction bar run as close to the center line of the axle as physically possible. This means right up against or actual on the differential. It you can picture this the shackle front will allow for the frnt -rear movement the leaf spring cycles in and becasue its only a single bar very close to center it will allow for extreme articulation without binding. By using jonny joints or other similar joints that allow allow of lateral rotation at or near center will allow for all the flexibility you need.
This type of single A-traction bar is what dominates leaf sprung long travel/articulation off road rigs. It can be made plenty beefy as well. The issue with these for a company to offer is they require some creativity in finding or fabbing a front mount location. One of there other benefits though is they can be designed so not only do they offer complete suspension travel and articulation without binding but also can protect your drive line and pinion from damage with only the very minimal of ground clearance loss. Many times far less than a number of dual traction bar setups do.
In side this single arm A frame traction bar basic design there are a number of ways to achieve each of the points. Each have there pros and cons. I will farther down to list the various types I have found and try to list what I have learned about them. In no way take this as I have any kind of real world expeirnce with them. I can only go off what I have read been told and have seen with my own eyes as some of these rigs were put there their paces with these different setups in use. I can tell you this out of all the really serous off road rigs that are using leaf springs for what ever reason none of them use dual traction bars ( one for each side of the axle) They ALL use a single traction bar in some version of the A frame design. That shoudl be very telling for those looking for the utmost in performance when it comes to suspension travel and articulation.
Obviously for position the goal is as close to the center( pinion location) as possible for the 2 axle mount points. How you fab you mount points both on the axle as well as up front will dictate whether it goes next the differential on one of the axle tubes or actually on the differential itself.
For the front mount if there is no cross member to attach mount points to some thing will have to be added which can be a full or partial cross bar. It can be bolt or weld in.
How you setup but both the length of your A bar setup as well as the shackle or whatever front pivot point used will effect how the rear end reacts when torque is applied i.e. Anti squat. So it really does matter how you setup these things up based what you are looking for in performance. IMO unless its for mud bogging or some competitive sport where you really want to plan the tires hard (high positive anti squat) you want to get as close to a neutral balanced point as possible. As this is a leaf sprung system this will not be an exact science like it woudl be with a 4 link for example. With a leaf spring locating the axle, there is a lot of flexibility and the axle doesn't really move in one perfectly defined path. But leafs do work well its just there is a bit more slop to the calculations.
The assumption is that the leaf spring's contribution to locating the axle can be represented by a horizontal link at the axle center line. Given that to find the side view instant center, you draw a horizontal line through the axle center line. Then you draw a line through the pivot points of the shackle. It doesn't matter if the shackle is in tension or compression or whatever angle. Where those two lines intersect is the instant center.
Picture copied from "Gordon" on pirate4x4:
Squat/antisquat effects on vehicle
SO while it seems lowering the bars connection to shackle point will lower anti-squat the reason for this is becasue it moves your instant center forward. What really makes a difference is making your bar traction bar longer. While as you can see from the first pic making the shackle angle longer will also more the instant center forward keep in mind the farther you slope the shackle from vertical the more stress(horizontal force) you will put on your springs. If you were to have a flat shackle it would be just like having a one link. It is best to keep shackle angle at 90 degrees to bar so force is directly upward and there is less stress. Given that changing the bar length is the best way to effect anti-squat.
So what does all this mean? Heck if I know!! No but seriously it can get confusing as we are dealing with a number of different factors.
* We are dealing with primary concern that got everyone needing traction bars to begin with: stopping pinion rotation from axe wrap.
* Then you are needing to set it up to prevent any binding thru the suspension travel.
* Lastly how the directing of force effects how the rear axle reacts when torque is sent thru to the wheels. Anti-Squat We want a neutral setting IMO. This will prevent wrap but also any wheel hop.
So in general you will want your traction bar to be at least as long to mount where your leaf springs front mount is. Actually a bit longer is better and certainly much better than being shorter. Its best if using a shackle to try and keep it perpendicular to the top bar.
With a shackle design the use of jonny joints gives the needed twisting to allow for all the articulation of the axle. The shackle allows for natural arc of the axle travel to happen with out binding and flexing the leafs and stressing the joints.
There is another type of front mount setup that also works calling a "slip and twist". It works similar to the slip joint on the driveshaft but also allows it to spin free (no teeth) So instead of high degree jonny joints and a shackle The slip joint can length and compress for front to rear travel and rotate for the twisting from articulation. It can be a simple hemi joint or bushing setup for mounting then. The main drawbacks with this type is friction, clunky you will fee it when you get on the pedal. It takes making sure the shaft is always well greased. Out tubing needs to be able to take the stress as well.
I will try to post up as many varying setup of the single ladder traction bar. Everything from shackle, fixed, slip and twist, various hybrids, etc.
One thing for sure if a traction bar setup can somehow take the place of a sway bar its gonna have issues with binding it has to same as with a sway bar.