Better anti wrap ideas? (2 Viewers)
- Thread starter troyintahoe
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Been following for the same reasons as above. It looks like from a bang for the buck perspective a triangular bar with a shackle at the crossmember is preferred. A 4 link might be better, but requires quite a bit more thought and $$ into it's set-up. The overload springs used as anti-wrap might allow the axle to load up and slip repeatedly maybe causing shock loads?
So regarding the triangle type: I was looking at making the link the same radius as the front half of the spring. Make the bar as level as possible to reduce squat/lift. I was planning for hard mounting at the axle (hiem and/or poly) and use a softer bushing at the crossmember shackles. Try to center the arm on the axle from driver to passenger side. Maybe not use a jam washer at the shackle end of the bar to allow for rotation, not like it will unscrew...
The single link seems like it would concentrate a large amount of force onto a "small" section of the axle. Is this not a real concern?
Any real concern with axle housing and bracket that needs attention? Most of the ones you see are just 2 pieces of plate or 2" square tube.
Have to keep following along, maybe the light will come on for me...
So regarding the triangle type: I was looking at making the link the same radius as the front half of the spring. Make the bar as level as possible to reduce squat/lift. I was planning for hard mounting at the axle (hiem and/or poly) and use a softer bushing at the crossmember shackles. Try to center the arm on the axle from driver to passenger side. Maybe not use a jam washer at the shackle end of the bar to allow for rotation, not like it will unscrew...
The single link seems like it would concentrate a large amount of force onto a "small" section of the axle. Is this not a real concern?
Any real concern with axle housing and bracket that needs attention? Most of the ones you see are just 2 pieces of plate or 2" square tube.
Have to keep following along, maybe the light will come on for me...
Cruiserdrew
On the way there
I really don't know any of the engineering details behind an anti-wrap bar. What I do know, is that my FJ40 has been on some very hard trails with low gearing and a traditionally designed ladder type bar. My pinion is set up to run a c/v shaft, and there have been no issues with the wrap bar and a short shackle up front to allow it to move around a bit. My springs have not sagged prematurely and flex is decent but not as good as a coil-over 4 link.
I think this thread got side tracked a bit. Wrap bars work just great at preventing broken pinions. That is all that's needed for 99.9% of 4wheelers. It is easier on your springs to have a wrap bar, then to not have one. A strong cross member, a shackle and a well made ladder bar are all that's needed. Fancier set-ups can work well too, but are not needed in most cases. Ladder bars work.
In the end, no doubt 4 links are better, just not realistic for most driveway builds.
I think this thread got side tracked a bit. Wrap bars work just great at preventing broken pinions. That is all that's needed for 99.9% of 4wheelers. It is easier on your springs to have a wrap bar, then to not have one. A strong cross member, a shackle and a well made ladder bar are all that's needed. Fancier set-ups can work well too, but are not needed in most cases. Ladder bars work.
In the end, no doubt 4 links are better, just not realistic for most driveway builds.
ntsqd
technerd
I'm in crunch mode for Vegas to Reno & have a huge work project due tomorrow. I'll come back next week.
Waggoner5 (Gary) had the coolest link setup that I have seen yet. I don't know the ins and outs of the geometry but I bet it works great.
LINK (start at post #6)
Please post up pros and cons of this set up.
Dynosoar
Essentially no difference between a ladder setup and Gary's setup. Gary just has the two axle points inline like a 80 series suspension instead of top to bottom.
The big thing with one like Gary's. You have to make the single link very strong.. You are relying on that single bar to hold a lot of pressure.
FWIW...Here is what I came up with for tack bar and its worked really well for 2 years now.
I dont have much to contribute as far a tech regarding this, but I got the opinions for the folks who know better here on mud and whipped this lil bugger up. I DO have AAL's in my leaves at all 4 corners, but Im typically LOADED when wheeling too. I carry lots of tools and spare stuff, plus 10 gal of fuel (usually).
Its 1/4 in wall 1.5 OD tubing, weld in bung to home brew x member and shackle. The bracket I got from Ruff Stuff!
Chicago
I dont have much to contribute as far a tech regarding this, but I got the opinions for the folks who know better here on mud and whipped this lil bugger up. I DO have AAL's in my leaves at all 4 corners, but Im typically LOADED when wheeling too. I carry lots of tools and spare stuff, plus 10 gal of fuel (usually).
Its 1/4 in wall 1.5 OD tubing, weld in bung to home brew x member and shackle. The bracket I got from Ruff Stuff!
Chicago
Nice setup Chicago. What defines the geometry of the A Frame? How about shackle length? Are people just kinda guessing and throwing these together or is there a method to sizing these puppies. I have taken classes on stress, strain, buckling and the like but I'm not confident about geometry setup. I don't feel I have enough knowledge to make the correct assumptions about the movement of the suspension to design my own. So...
Why shackle length? Why not shorter or longer?
How about width of A-Frame / Truss?
I know there is probably not a definite answer but I'm interested in finding out as much as possible.
Clean install Chacago. I followed your SOA build and it looks great.
Why shackle length? Why not shorter or longer?
How about width of A-Frame / Truss?
I know there is probably not a definite answer but I'm interested in finding out as much as possible.
Clean install Chacago. I followed your SOA build and it looks great.
Mark W
Yep, I really don't really care that much I guess.
This is an important point if the rig sees a lot of variance in loading... a heavy load with lower the front mount in relation to the axle and the spring compress... forcing a preload on the traction bar... trying to s curve the springs. this will shorten the life of the springs... by a LOT in some cases... BTDT.
getting the geometry correct is a lot more complicated than just building you setup for max clearance or to match your driveshaft length.
In a rig that only does day trips in the rocks and doesn't carry much load it is not as big a deal
Mark...
Chicago
Why did you make your ladder bar the length you did?
Why did you make your ladder bar the length you did?
Mark W
Yep, I really don't really care that much I guess.
the simple addition of a full length overoad spring... not a flat one... and not one that angles down... but an extra, heavy, full length leaf to the pack will probably do all that a wagon will ever need. Few wagons are hard core rock crawlers bouncing on one rear tire up a ledge
and few are big block mud racers either
How often to FJ60s with OME heavies bust a pinion due to spring wrap? I imagine that is happens... but... how often have you heard of it?
I was having spring wrap concerns in my 350 powered FJ40 with 275:1 gearing
with th addition of a couple of full length leaves from an chevy half tone rear pack... I have no axle wrap any more and th ride is not enough stiffer to notice... gained about 2-3 inches of lift, which was my primary reason for th install.
a half length leaf will not work as well to reduce wrap... and it will be stiffer
a shorter overload that is straight will work great to prevent "too much" wrap... and will have little effect on he performance of the suspension.
I have built a few anti-torque bars... but for the heavy and varying loading that my rigs see... I have moved away from that and instead have found myself leaning toward properly set up springs instead.
Mark...
and few are big block mud racers either
How often to FJ60s with OME heavies bust a pinion due to spring wrap? I imagine that is happens... but... how often have you heard of it?
I was having spring wrap concerns in my 350 powered FJ40 with 275:1 gearing
with th addition of a couple of full length leaves from an chevy half tone rear pack... I have no axle wrap any more and th ride is not enough stiffer to notice... gained about 2-3 inches of lift, which was my primary reason for th install.
a half length leaf will not work as well to reduce wrap... and it will be stiffer
a shorter overload that is straight will work great to prevent "too much" wrap... and will have little effect on he performance of the suspension.
I have built a few anti-torque bars... but for the heavy and varying loading that my rigs see... I have moved away from that and instead have found myself leaning toward properly set up springs instead.
Mark...
Honestly...
It was based EXCLUSIVELY on where I was able to run the x member on the frame rails.
There is SOOOOOO much crap tucked up there, it was an act of GOD that I was able to find one little spot to run it and clear everything.
From there, I got the shackle dimension set with the brackets on the housing, and just ran the top tube to where the shackle sat about vertical.
Wether it was right or wrong....I donno.
Like Mark W is saying, the beef spring packs probably help a great deal.
I tend to go for the more agressive trails too, so its not like Im running pole line roads with it. Its held up pretty well thus far.
Chicago
Hate to say it, but I really eye balled everything and utilized the space that I had. Again, the x member location dictated almost everything. As far as the shackle length...I wanted it as flat as I could without it hanging down too low.
The way I looked at it, something in the flavor of what others here have had success with would be better than nothing.
Thanks for the kudos on the build!
Chicago
Hate to say it, but I really eye balled everything and utilized the space that I had. Again, the x member location dictated almost everything. As far as the shackle length...I wanted it as flat as I could without it hanging down too low.
The way I looked at it, something in the flavor of what others here have had success with would be better than nothing.
Thanks for the kudos on the build!
Chicago
This is one of the biggest things..
It is not always the best location that puts a bar somewhere. It is where it will fit.
Mark, You are still keeping stock axles alive with 42's and bigger as well right??
Did a search on pirate4x4 for awhile since they do more fab and custom work. Here is a good read with pics that I liked. No affiliation and I'm not an expert by far but this helped me out. The pictures didn't post but the read still helps if you've got a few minutes.
Axle Wrap Prevention
by: John Nutter
A look at axle wrap prevention devices
Don't let this happen to your springs. Springs can deflect to take this shape under load, when the pinion has rotated up in reaction to the torque applied to the tires.
Axle wrap is a problem that plagues leaf sprung vehicles with soft springs, particularly those that are set up SOA (Spring Over Axle). Axle wrap is something different than wheel hop. Wheel hop is when an axle on your 4x4 rapidly hops up and down. Axle wrap is unwanted suspension movement that allows the pinion angle to change. Wheel hop is annoying and could cause drivetrain breakage, but usually it's not the actual hopping that breaks parts, it's the axle wrap that results from the hop that causes drivelines to bind and breaks yokes, drive shafts and sometimes even pinions.
It's hard to reduce wheel hop without going to stiffer springs or shocks which can reduce articulation and change the ride and handling characteristics. Axle wrap can be nearly completley eliminated with no effect on articulation or handling.
Some of the basic concepts
There are few things to know and definitions to understand before we begin the discussion:
• Wheel Hop: Unwanted or uncontrolled suspension movement in the vertical plane, usually this problem seen most dramatically when a lot of torque is applied to the wheels.
• Axle Wrap : Unwanted change in the pinion angle.
• Ladder Bar: On each side : two bars connected from a point on the frame forward of the axle, to a vertical bracket or mount on the axle so it forms a triangle, meant to control pinion angle and sometimes providing forward-rearward location of the axle.
• 4 Link: On each side there will be two bars mounted from two different points on the frame to two different mounting points on the axle, generally in such a way that they do not form a triangle. A 4 link is meant to control both pinion angle and forward-rearward location of the axle. This is the suspension mechanism used in the newer factory coil sprung Jeeps like the Grand Cherokee or the TJ. It is possible to use a 4 link with leaf springs, however some device must be used to relieve the binding caused by the springs and 4 links traveling through different arcs if maximum articulation is to be achieved.
• Triangulation: The triangle is the most rigid geometric shape, this is because a triangle can not change shape without the length of one of the sides changing. Ladder bars attached at to the axle at two corners and the frame at the third obviously achieve triangulation, because the resulting structure is triangle shaped.
I'll talk about some of the types of products currently available that claim to reduce axle wrap or wheel hop on the rear axle, and possibly debunk a few. I'm not going to pick on any specific product or vendor because there are several companies who make or sell most of these. Note: We have generated these opinions by watching and using many of these suspensions over the years. These rules generally apply to each individual type of suspension. Each individual suspension behaves differently due to variances in spring rate, shock stiffness, shock attachment points, tire grip, and suspension geometry, but these basic rules generally apply. Stiffer springs and shocks reduce both wheel hop and axle wrap, but at the cost of articulation.
This is one of the more common 'anti wheel hop' setups. A mount is fastened to the spring pack by the U-bolts, at the other end is a bracket attached rigidly to the frame of the vehicle. There is often a radius arm type bushing at the forward end of the bar
Another setup, similar to the first except that it uses a single bar attached on top of the differential.
Reaction against the torque of a spinning wheel pulls on the bar and pushes on the spring. This tends to combine with the springs natural tendency to go into an "S" shape when under torque to cause more wheel hop.
The bar actually exerts more force on the spring as it gets farther away.
Single bar setups
Single bar setups are the most common that I've seen, probably because people are concerned with articulation and want to avoid limiting articulation by putting in a ladder bar or 4 link system that may travel through a different arc than the leaf springs and cause an articulation reducing bind. Most of the time rock crawlers locate the bar above the axle tube, differential housing or spring pack to avoid reducing ground clearance,
Fixed length single bar systems located above the springs.
In both of these systems the front half of the spring is going to be placed under compression as you accelerate because the pinion wants to climb in reaction to the axle torque being applied to the ground through the wheels. As most people know, when loaded like this, leaf springs tend to go into an "S" shape. This "S" shape makes the forward half of the spring shorter, and the compression effect from this type of single bar setup can actually make axle wrap worse by forcing the spring to get even shorter, putting it into more of an "S" shape and pointing the pinion higher. Obviously a stiffer spring would offer more resistance against going into an "S shape, but you wouldn't need any anti-wrap bar at all if your springs were that stiff.
In other words, this type of setup is depending on the spring to stay rigid in order to achieve the triangulation it needs to hold the pinion angle steady. This is a bad idea because springs by their very nature are designed to bend. It is made even worse because the compression effect from this setup forces the front half of the spring to bend even more in the way that it naturally wants to bend during axle wrap. This may even possibly increase axle wrap. The unwanted effects will get worse as the rear mount gets higher. The more common single bars that locate directly above the leaf springs don't really cause much more axle wrap, but they don't help it either. All of these fixed length single bars setups reduce articulation because they don't allow for spring length to change during compression and extension.
This systems simply doesn't work well. It allows motion in every conceivable direction, including housing rotation.
Variable length, single bar systems located above the springs
Take a good look at the diagram to the left. I recently ran across this system being offered for sale. I can't put a picture of the actual product in the article, but not reducing articulation is clearly the primary design intent and axle wrap control is a secondary consideration. It doesn't do anything for axle wrap control or wheel hop. It's a single bar attached over the top of the differential housing. It's got a heim joint at the rear, and a swing shackle with a pivot to allow for twisting at the front. This bar is allowed to change length by several inches due to the swinging shackle. The swinging shackle eliminates any bind because it allows the bar to change length as the spring length changes during compression or extension. There is not even an attempt to triangulate with the spring and prevent axle wrap. The heim joint where it attaches to the housing allows the housing to rotate as if the bar weren't even there. This type of bar won't make axle wrap worse, and it won't make it better. It does nothing but take up space and empty your wallet. The addition of a lower bar also attached to the housing by a heim joint and attached to the existing bar near the forward end would make this a very effective and attractive system, it would also make it a ladder bar.
This system is effective because it does the exact opposite of what a bar located above the springs does. This system puts the spring under tension during acceleration, which tends to pull it straight and prevent it from going into the dreaded "S" shape.
Single bar systems located below the springs
Single bars located below the springs actually help solve the axle wrap problem somewhat. Most rock crawlers avoid these setups because they don't want to reduce ground clearance, but they are fairly popular with mud boggers. These bars work by by putting the forward half of the spring under tension when axle wrap tries to occur. This tension fights the springs natural tendency to get shorter and turn into an "S" shape by pushing the axle housing back and pulling the springs straight. These bars are still not totally effective for axle wrap control because they depend on the spring to be rigid for triangulation, but they are more effective than bars located above the spring because they tend to straighten the spring when axle wrap occurs making the spring seem stiffer an generally reducing wrap by preventing the spring from going into an "S" shape.
These bars get more effective as the bottom mount for the bar gets lower, but they also lose more ground clearance as the bottom mount gets lower. These bars also somewhat limit articulation because the bar and the spring will swing through different arcs and bind. I'm happy to report that I've never seen anyone selling a setup like this with a swinging shackle at the front end of the bar, because that would make the system useless by allowing the length of the bar to change and preventing the bar from putting tension on the spring.
Double Bar Setups
Ladder bars and 4 links both fall into the category of double bar setups because they each have bars located above and below the axle tube. Most custom three bar setups or setups with a wishbone for the top bar also fall into this category. Double bar setups generally work well for controlling axle wrap.
A ladder cannot allow the pinion angle to change unless a bar bends or the height of the forward mounting point changes. The shackle holds the forward mounting point at a steady height in this example.
Ladder bars
A Ladder bar is a triangle formed by two long rods and the mount for the axle end. Because the ladder bar is rigid and firmly attached to the axle it doesn't depend on the springs for triangulation. Axle wrap can't occur if the end of the ladder bar away from the axle is held at a steady height because this prevents the axle from rotating and prevents the pinion angle from changing. The springs can't go into an "S" shape unless the pinion angle rises. This is probably the simplest system that will control axle wrap.
I've got a swing shackle on the leading edge of my ladder bar to allow it to follow the arc of the springs and prevent binding, and I've got a threaded portion to prevent bind as the axle articulates. Although the shackle can swing forward and back a few inches, it holds the forward end of the ladder bar at the nearly the same height throughout it's swing. The shackle moves less then an inch forwards and backwards throughout the entire travel of my suspension. I've done ramp testing with the ladder bar on and off and found no measurable difference. In theory there should be some bind because the forward edge of the ladder bar is held at a constant height by the shackle and this forces the pinion angle to change in a controlled manner as the axle droops. Ramp testing with the shackle disconnected showed that the forward end of the bar tended to stay within a few inches of the height where the shackle would hold it throughout the range of suspension travel, the bind is so minor that it affects nothing. Your results will vary in this depending on the design of the bar, the mount, and the suspension geometry on your vehicle.
A 4 Link cannot allow the pinion angle to change unless a bar bends. There are ways to avoid binding as the suspension cycles.
4 Links and similar designs
A 4 link is more complicated than a ladder bar and can also achieve more. Race car builders are capable of building many desirable handling characteristics into a 4 link set up. A 4 link system controls the pinion angle just as effectively as a ladder bar because it doesn't depend on the springs for triangulation. Instead the upper and lower bars triangulate off each other. Many people build 4 link systems where one set of arms is tapered inwards, or even with one end siamesed together to form a wishbone. This is an effective way to locate the axle side to side without inducing any bind in the suspension.
The problem with a 4 link is that it may not follow the same arc as the spring does throughout the range of movement of the suspension. It may possible to get it close enough that it wouldn't hurt much, but it would be difficult and might cause other undesirable handling problems. A shackle on any of the bars would render the suspension completely ineffective because a 4 link depends on the bars being a fixed length and the mounts being rigid for control. A good way to get around the spring bind problem on a 4 link setup is to put shackles at both ends of the springs or go to a spring floating system similar to what drag racers use. The spring floating systems attach the spring pack to the axle, but allow it to move forward and backward on the housing to eliminate bind.
Conclusions
Be wary of single bar systems when shopping for axle wrap control. All single bar systems depend on the spring pack itself to remain rigid in order to be effective, and this is contrary to the goal of most suspension designers. A ladder bar is always a safe bet because of it's simplicity and rigidity. A 4 Link may offer more advantages than a ladder bar, but you will have to put considerable thought into your system to take advantage of this.
Axle Wrap Prevention
by: John Nutter
A look at axle wrap prevention devices
Don't let this happen to your springs. Springs can deflect to take this shape under load, when the pinion has rotated up in reaction to the torque applied to the tires.
Axle wrap is a problem that plagues leaf sprung vehicles with soft springs, particularly those that are set up SOA (Spring Over Axle). Axle wrap is something different than wheel hop. Wheel hop is when an axle on your 4x4 rapidly hops up and down. Axle wrap is unwanted suspension movement that allows the pinion angle to change. Wheel hop is annoying and could cause drivetrain breakage, but usually it's not the actual hopping that breaks parts, it's the axle wrap that results from the hop that causes drivelines to bind and breaks yokes, drive shafts and sometimes even pinions.
It's hard to reduce wheel hop without going to stiffer springs or shocks which can reduce articulation and change the ride and handling characteristics. Axle wrap can be nearly completley eliminated with no effect on articulation or handling.
Some of the basic concepts
There are few things to know and definitions to understand before we begin the discussion:
• Wheel Hop: Unwanted or uncontrolled suspension movement in the vertical plane, usually this problem seen most dramatically when a lot of torque is applied to the wheels.
• Axle Wrap : Unwanted change in the pinion angle.
• Ladder Bar: On each side : two bars connected from a point on the frame forward of the axle, to a vertical bracket or mount on the axle so it forms a triangle, meant to control pinion angle and sometimes providing forward-rearward location of the axle.
• 4 Link: On each side there will be two bars mounted from two different points on the frame to two different mounting points on the axle, generally in such a way that they do not form a triangle. A 4 link is meant to control both pinion angle and forward-rearward location of the axle. This is the suspension mechanism used in the newer factory coil sprung Jeeps like the Grand Cherokee or the TJ. It is possible to use a 4 link with leaf springs, however some device must be used to relieve the binding caused by the springs and 4 links traveling through different arcs if maximum articulation is to be achieved.
• Triangulation: The triangle is the most rigid geometric shape, this is because a triangle can not change shape without the length of one of the sides changing. Ladder bars attached at to the axle at two corners and the frame at the third obviously achieve triangulation, because the resulting structure is triangle shaped.
I'll talk about some of the types of products currently available that claim to reduce axle wrap or wheel hop on the rear axle, and possibly debunk a few. I'm not going to pick on any specific product or vendor because there are several companies who make or sell most of these. Note: We have generated these opinions by watching and using many of these suspensions over the years. These rules generally apply to each individual type of suspension. Each individual suspension behaves differently due to variances in spring rate, shock stiffness, shock attachment points, tire grip, and suspension geometry, but these basic rules generally apply. Stiffer springs and shocks reduce both wheel hop and axle wrap, but at the cost of articulation.
This is one of the more common 'anti wheel hop' setups. A mount is fastened to the spring pack by the U-bolts, at the other end is a bracket attached rigidly to the frame of the vehicle. There is often a radius arm type bushing at the forward end of the bar
Another setup, similar to the first except that it uses a single bar attached on top of the differential.
Reaction against the torque of a spinning wheel pulls on the bar and pushes on the spring. This tends to combine with the springs natural tendency to go into an "S" shape when under torque to cause more wheel hop.
The bar actually exerts more force on the spring as it gets farther away.
Single bar setups
Single bar setups are the most common that I've seen, probably because people are concerned with articulation and want to avoid limiting articulation by putting in a ladder bar or 4 link system that may travel through a different arc than the leaf springs and cause an articulation reducing bind. Most of the time rock crawlers locate the bar above the axle tube, differential housing or spring pack to avoid reducing ground clearance,
Fixed length single bar systems located above the springs.
In both of these systems the front half of the spring is going to be placed under compression as you accelerate because the pinion wants to climb in reaction to the axle torque being applied to the ground through the wheels. As most people know, when loaded like this, leaf springs tend to go into an "S" shape. This "S" shape makes the forward half of the spring shorter, and the compression effect from this type of single bar setup can actually make axle wrap worse by forcing the spring to get even shorter, putting it into more of an "S" shape and pointing the pinion higher. Obviously a stiffer spring would offer more resistance against going into an "S shape, but you wouldn't need any anti-wrap bar at all if your springs were that stiff.
In other words, this type of setup is depending on the spring to stay rigid in order to achieve the triangulation it needs to hold the pinion angle steady. This is a bad idea because springs by their very nature are designed to bend. It is made even worse because the compression effect from this setup forces the front half of the spring to bend even more in the way that it naturally wants to bend during axle wrap. This may even possibly increase axle wrap. The unwanted effects will get worse as the rear mount gets higher. The more common single bars that locate directly above the leaf springs don't really cause much more axle wrap, but they don't help it either. All of these fixed length single bars setups reduce articulation because they don't allow for spring length to change during compression and extension.
This systems simply doesn't work well. It allows motion in every conceivable direction, including housing rotation.
Variable length, single bar systems located above the springs
Take a good look at the diagram to the left. I recently ran across this system being offered for sale. I can't put a picture of the actual product in the article, but not reducing articulation is clearly the primary design intent and axle wrap control is a secondary consideration. It doesn't do anything for axle wrap control or wheel hop. It's a single bar attached over the top of the differential housing. It's got a heim joint at the rear, and a swing shackle with a pivot to allow for twisting at the front. This bar is allowed to change length by several inches due to the swinging shackle. The swinging shackle eliminates any bind because it allows the bar to change length as the spring length changes during compression or extension. There is not even an attempt to triangulate with the spring and prevent axle wrap. The heim joint where it attaches to the housing allows the housing to rotate as if the bar weren't even there. This type of bar won't make axle wrap worse, and it won't make it better. It does nothing but take up space and empty your wallet. The addition of a lower bar also attached to the housing by a heim joint and attached to the existing bar near the forward end would make this a very effective and attractive system, it would also make it a ladder bar.
This system is effective because it does the exact opposite of what a bar located above the springs does. This system puts the spring under tension during acceleration, which tends to pull it straight and prevent it from going into the dreaded "S" shape.
Single bar systems located below the springs
Single bars located below the springs actually help solve the axle wrap problem somewhat. Most rock crawlers avoid these setups because they don't want to reduce ground clearance, but they are fairly popular with mud boggers. These bars work by by putting the forward half of the spring under tension when axle wrap tries to occur. This tension fights the springs natural tendency to get shorter and turn into an "S" shape by pushing the axle housing back and pulling the springs straight. These bars are still not totally effective for axle wrap control because they depend on the spring to be rigid for triangulation, but they are more effective than bars located above the spring because they tend to straighten the spring when axle wrap occurs making the spring seem stiffer an generally reducing wrap by preventing the spring from going into an "S" shape.
These bars get more effective as the bottom mount for the bar gets lower, but they also lose more ground clearance as the bottom mount gets lower. These bars also somewhat limit articulation because the bar and the spring will swing through different arcs and bind. I'm happy to report that I've never seen anyone selling a setup like this with a swinging shackle at the front end of the bar, because that would make the system useless by allowing the length of the bar to change and preventing the bar from putting tension on the spring.
Double Bar Setups
Ladder bars and 4 links both fall into the category of double bar setups because they each have bars located above and below the axle tube. Most custom three bar setups or setups with a wishbone for the top bar also fall into this category. Double bar setups generally work well for controlling axle wrap.
A ladder cannot allow the pinion angle to change unless a bar bends or the height of the forward mounting point changes. The shackle holds the forward mounting point at a steady height in this example.
Ladder bars
A Ladder bar is a triangle formed by two long rods and the mount for the axle end. Because the ladder bar is rigid and firmly attached to the axle it doesn't depend on the springs for triangulation. Axle wrap can't occur if the end of the ladder bar away from the axle is held at a steady height because this prevents the axle from rotating and prevents the pinion angle from changing. The springs can't go into an "S" shape unless the pinion angle rises. This is probably the simplest system that will control axle wrap.
I've got a swing shackle on the leading edge of my ladder bar to allow it to follow the arc of the springs and prevent binding, and I've got a threaded portion to prevent bind as the axle articulates. Although the shackle can swing forward and back a few inches, it holds the forward end of the ladder bar at the nearly the same height throughout it's swing. The shackle moves less then an inch forwards and backwards throughout the entire travel of my suspension. I've done ramp testing with the ladder bar on and off and found no measurable difference. In theory there should be some bind because the forward edge of the ladder bar is held at a constant height by the shackle and this forces the pinion angle to change in a controlled manner as the axle droops. Ramp testing with the shackle disconnected showed that the forward end of the bar tended to stay within a few inches of the height where the shackle would hold it throughout the range of suspension travel, the bind is so minor that it affects nothing. Your results will vary in this depending on the design of the bar, the mount, and the suspension geometry on your vehicle.
A 4 Link cannot allow the pinion angle to change unless a bar bends. There are ways to avoid binding as the suspension cycles.
4 Links and similar designs
A 4 link is more complicated than a ladder bar and can also achieve more. Race car builders are capable of building many desirable handling characteristics into a 4 link set up. A 4 link system controls the pinion angle just as effectively as a ladder bar because it doesn't depend on the springs for triangulation. Instead the upper and lower bars triangulate off each other. Many people build 4 link systems where one set of arms is tapered inwards, or even with one end siamesed together to form a wishbone. This is an effective way to locate the axle side to side without inducing any bind in the suspension.
The problem with a 4 link is that it may not follow the same arc as the spring does throughout the range of movement of the suspension. It may possible to get it close enough that it wouldn't hurt much, but it would be difficult and might cause other undesirable handling problems. A shackle on any of the bars would render the suspension completely ineffective because a 4 link depends on the bars being a fixed length and the mounts being rigid for control. A good way to get around the spring bind problem on a 4 link setup is to put shackles at both ends of the springs or go to a spring floating system similar to what drag racers use. The spring floating systems attach the spring pack to the axle, but allow it to move forward and backward on the housing to eliminate bind.
Conclusions
Be wary of single bar systems when shopping for axle wrap control. All single bar systems depend on the spring pack itself to remain rigid in order to be effective, and this is contrary to the goal of most suspension designers. A ladder bar is always a safe bet because of it's simplicity and rigidity. A 4 Link may offer more advantages than a ladder bar, but you will have to put considerable thought into your system to take advantage of this.
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Great article!
Mark W
Yep, I really don't really care that much I guess.
I am running 40s now... 39.5x18 boggers... FF rear... eating birfields too often up front.
On my other rig when I was running 42s and a coil spring suspension with a lot of anitsquat built in... I shattered three semifloating rear axles
I am swapping in FZJ80 axles with Elockers and the full longfield treatment up front over the next year sometime.
Mark...
ntsqd
technerd
Interesting that the author of that article condemns single bar systems for the loads placed on the springs (& erroneously states that it will force a 'S' curve when in reality it forces a bend, or tries to, in the natural direction of the spring's existing arc), yet completely fails to mention the loads that a ladder bar places on the springs or the 'S' curve that it will force unless the housing is allowed to rotate relative to the spring.
AFAIC the article is a regurgitation of conjecture, that has never been proved or disproved, and is presented as fact when it is not.
Just because it's on the net somewhere does not mean that it is true, correct, or even partially valid. Especially from that site.
Consider just an axle mounted on leaf springs. No other linkages of any sort.
Now compress that suspension. Does the pinion angle change? How much?
Extend that suspension. Does the pinion angle change? How much?
Once you understand where and by how much the pinion angle changes through the range of suspension travel, Then you can evaluate what linkages will work and last and what won't. Do not fall into the trap of allowing others to think it through for you. Think it through yourself. If you have to, mock it up using only the main leaf of a soft spring. The common assumption of how the pinion angle changes through the range of suspension travel of a leaf sprung suspension is wrong. It is wrong because it fails to account for the intentional bending of the leaf spring in it's normal function.
If that seems overly opinionated, consider that my job pays me to have a considered and thought-through opinion on many topics and this is one of those, then refer to my sig file.
AFAIC the article is a regurgitation of conjecture, that has never been proved or disproved, and is presented as fact when it is not.
Just because it's on the net somewhere does not mean that it is true, correct, or even partially valid. Especially from that site.
Consider just an axle mounted on leaf springs. No other linkages of any sort.
Now compress that suspension. Does the pinion angle change? How much?
Extend that suspension. Does the pinion angle change? How much?
Once you understand where and by how much the pinion angle changes through the range of suspension travel, Then you can evaluate what linkages will work and last and what won't. Do not fall into the trap of allowing others to think it through for you. Think it through yourself. If you have to, mock it up using only the main leaf of a soft spring. The common assumption of how the pinion angle changes through the range of suspension travel of a leaf sprung suspension is wrong. It is wrong because it fails to account for the intentional bending of the leaf spring in it's normal function.
If that seems overly opinionated, consider that my job pays me to have a considered and thought-through opinion on many topics and this is one of those, then refer to my sig file.
I am actually curious to know if anyone has run the single bar type link to the bottom of the axle housing.
That might actually do the trick.. As long as handling characteristics are not hampered too much by it..
That might actually do the trick.. As long as handling characteristics are not hampered too much by it..
