Looking for opinions on what to do with a linked TJ long arm suspension. My initial thoughts were to go with a standard long arm system, but instead of mounting them further back on the frame from the axles, I would kill two birds with one stone and mount them at or near the stock locations and move the spring perches and shock mounts forward to stretch the wheelbase. Is this a mistake? Would it be better to just get longer arms, mount them further towards the center of the rig, and do away with the stock mounts altogether? I still want the stretch (6" front, 4" rear) and I want alot of suspension travel(thinking coilovers)...do longer arms mean better angulation for longer travel? Or is there such a thing as too long?
I've heard that the only difference between long and short arms, granted the lift is under 5", is that the arm geometry results in a better ride, but doesn't help flex(determined by spring and shock length in either case). I disagree with this because shorter arms will bind sooner, especially in a flex situation.
Also, What's the benefit to a triangulated suspension other than removal of the track bar? triangulated 4-link compared to a true 3-link? Radius Arm? I thought I've had my mind made up for me but I want to make sure I know everything I need before I start to spend time and money on it.
And if anyone tells me to get leafs.....:mad:
You would want the links as long as possible(within reason) to help keep them fairly flat when viewed from the side, this creates an instant center in front of the truck which helps with anti-squat...So if you are going to be lengthen the WB by 10 or so inches you still might be able to use the stock mounts.
Tri-4 link vs. Three link with panhard...a couple reasons, 1. higher roll axis. 2. To minimize roll induced rear steer. 3. More stable, etc. etc.
AK20 Wrote:You would want the links as long as possible(within reason) to help keep them fairly flat when viewed from the side, this creates an instant center in front of the truck which helps with anti-squat...So if you are going to be lengthen the WB by 10 or so inches you still might be able to use the stock mounts.
Tri-4 link vs. Three link with panhard...a couple reasons, 1. higher roll axis. 2. To minimize roll induced rear steer. 3. More stable, etc. etc.
All true. But you don't want too much anti squat. You want (forgive this) the right amount, you know, the whole three bears thing. Too much and it can create really odd handling and can hurt ya' on hill climbs. too little and it can unload your tyres.
Joe, you are up on your trig... envision how things work in your head. the longer the link, the less the axle will move forward or rearward. Therefore the chance of less flex steer. You will still want to thoroughly plan it out, there are a lot of key factors to keep in mind, especially being that it is going to be a dailey driver. There are some really good books to study four link geometry and theories... I will have to check what the names are. I have also found a few good things online as well...I'll try to find the link and post it.
mousee Wrote:All true. But you don't want too much anti squat. You want (forgive this) the right amount, you know, the whole three bears thing. Too much and it can create really odd handling and can hurt ya' on hill climbs. too little and it can unload your tyres.
Right, that should read the an instant center in front of the vehicle with help will help achieve anti squat upon acceleration...I totally agree to much anti squat can be a bad thing, I was more refering to longer links and instant center.
See if this helps. It's from Rock Krawler...
Long Arm Tech and the Rock Krawler Advantage
![[Image: re_system.jpg]](http://www.rockkrawler.com/spages/images/long%20arm%20tech/re_system.jpg)
![[Image: ft_system.jpg]](http://www.rockkrawler.com/spages/images/long%20arm%20tech/ft_system.jpg)
![[Image: rk_system.jpg]](http://www.rockkrawler.com/spages/images/long%20arm%20tech/rk_system.jpg)
System A:
System A is a long arm system that uses a radius arm front conversion with a track bar and a 4 link rear with a track bar.
Benefits:
1) Very smooth highway ride quality when accompanied by appropriate springs and shocks.
2) Excellent for full axle droop conditions or desert racing type situations.
3) Easy to install and uses stock factory mounts on the axles.
4) Does not require any exhaust modifications.
Draw Backs:
1) For the front end; the torque plain of the axle is over constrained. As mentioned above for full axle droop conditions this is fine. However; for articulation conditions the front axle is treated like a torsion tube. The only way to get articulation out of this type of system is to displace bushing material at the connections where the lower control arms attach to the axle, where the upper control arms attach to the axle, and where the upper and lower control arms meet. This causes premature wear of the bushings used in the system for heavy off road use. The more rigid the components are made, the less articulation you will get.
2) For the rear end; again we see the torque plain of the axle is over constrained. For articulation conditions the rear axle works in the same fashion as an OEM system, but does move a little more freely since all the control arms are effectively longer thus yielding larger radii of curvature.
3) Both front and rear axles side shift through articulation because of the effects of the track bars.
4) You have only two connections points holding the axle radially in place to the frame.
5) The front lower control arms are getting an extra bending stress due to the fact that the upper control arms attach directly to the lower control arms.
6) This type of system neither front nor rear is found in the highest levels of rock crawling.
System B:
System B is a long arm system that uses a four link front end with track bar and a tri-link rear.
Benefits:
1) Very smooth highway ride quality when accompanied by appropriate springs and shocks.
2) Excellent for full axle droop conditions or desert racing type situations up front.
3) The rear end is perfectly constrained by three points and functions well in all types of conditions.
Draw Backs:
1) For the front end; again we see the torque plain of the axle is over constrained. For articulation conditions the front axle works in the same fashion as an OEM system, but does move a little more freely since all the control arms are effectively longer thus yielding larger radii of curvature. Some of the manufacturers that use this type of front end are using mid length or effectively short arm upper control arms. This yields castor and pinion angle changes throughout the suspension cycle. If the front upper control arms are still "triangulated" this also causes a problem. The triangulation of the front upper control arms tries to maintain the axle centered in the vehicle. This fights the function of the track bar which causes a harsher ride and again impedes articulation.
2) For the rear end; the only draw backs are the axle is only connected to the frame by 3 points and in the most common company using this now has no adjustability of their rear triangulated member.
3) The front axle side shifts through articulation because of the effects of the track bar.
4) The rear axle can articulate more than the front end which is not preferred by most common rock crawlers. The ideal split is 60/40 front to rear.
5) Requires major exhaust modifications according to the most common manufacturer of this type of system.
6) This type of front end system is not found in the highest levels of rock crawling. The rear end design has been used effectively.
System C:
System C is a long arm system that uses an independent 3 link front end with track bar and a triangulated 4 link rear end.
Benefits:
1) Very smooth highway ride quality when accompanied by appropriate springs and shocks.
2) Excellent for full axle droop conditions and high articulation conditions on the front and the back.
3) The only front and rear end design with no natural binding points or premature wear points if implemented properly.
4) The front end can articulate as much if not more than the back end which provides excellent vehicle balance.
5) This type of system either the front end or the back end is found in the highest levels of rock crawling.
Draw Backs:
1) For the front end; the torque plain is only attached by 3 points.
2) For the rear end; the rear end is over constrained, but a properly implemented triangulated 4 link design functions like a tri-link design.
3) The front axle side shifts through articulation because of the effects of the track bar.
4) May require exhaust modifications.
Krawler Tech and Krawler Facts
About our X Factor Long Arm Systems
[SIZE=3]Rock Krawler's New X Factor are based on the same basic principals the old Gen I Systems were based on. How many points does it take to constrain a plane? The correct answer is 3. If a plane is constrained by any more than 3 points you have natural binding. Natural binding prevents flex and contributes to harshness of ride. With our 3 point or effective 3 point principals we have done what was once thought to be impossible; combining awesome highway ride quality and handling with unbeatable off road performance. [/SIZE]
Front End: The front end has three long arms pointing straight forward. The two lower control arms are below the axle and the front upper torque arm is above the axle. These members control front axle torque under braking and acceleration. All of this is done with no wear or bind at any joint. The front upper torque arm attaches to the axle housing where the original front upper control arm did. We give you the components to make the original cast upper mount into a greasable/serviceable spherical joint so there is no binding at that location. Then the front upper torque arm attaches to new brackets that bolt to the frame through another spherical joint. The new lower long arms attach to the frame via spherical joints through our new long arm brackets. The new lower long arms attach to the axle to the frame via spherical joints to the OEM axle brackets. All that means is no bind and no wear. The front end is controlled laterally via our track bar. All track bar geometry has been worked out to provide bump steer free operation. We switched to the X Factor design from our original GEN I design for ease of assembly.
Rear End: Rock Krawler's New X Factor rear end uses triangulated 4 link assemblies versus the GEN I tri-link assembly. A triangulated 4 Link assembly is an engineering representation of a tri-link assembly. This was done for ease of assembly. The functionality is exactly the same. The upper control arms are either straight or have bends in them to clear OEM exhaust systems. All connections for the upper arms are made through spherical joints for freedom of movement. The rear lower control arms attach at the frame through spherical joints at our new long arm brackets. The rear lower control arms attach at the axle through spherical joints at the OEM axle brackets. No bind - No wear. Perfect Suspension.
Strength of Materials
All of our X Factor lower long arms are made 1.75" diameter solid 1018-1020 cold rolled steel except for the TJ/LJ/YJ which are 2.0" Solid. We commonly use 1018-1020 cold rolled for it's excellent properties. Let's compare some strength of materials shall we?
The biggest concern customers have is the control arms bending. The easy way to take a look at bending properties of material without being concerned over arm length etc. is to compare the cross sections resistance to bending.
Here are a couple examples of the most commonly used materials.
For 1.75" diameter solid material I = 1/4pirexp4 = 1/4*3.14*.875exp4 = .460
For 2.00" diameter solid material I = 1/4pirexp4 = 1/4*3.14*1.000exp4 = .785
For 2" diameter 1/4" wall tubing I = 1/4piroexp4-1/4piriexp4= 1/4*3.14*1exp4 - 1/4*3.14*.75exp4 = .537
For 2" x 2" square tubing 1/4" wall I = 1/12bohoexp3-1/12bihiexp3 = 1/12*2*2exp3-1/12*1.5*1.5exp3 = .908
Cold Rolled 1018-1020 Steel's yield strength = 76,000 pounds
2" diameter 1/4" wall low carbon DOM tubing's yield strength = 26,100 to 34,800 pounds depending on mill.
2" x 2" 1/4" wall thickness electric resistance welded low carbon tubing's yield strength = 26,100 to 34,800 pounds depending on mill.
What does all this mean to you. Well, it is simple. According to the resistance to bending equations above anything 1.75" will bend easier than something 2" (1/4" wall) which will bend easier than 2" x 2" square tubing 1/4" wall. However this is only a geometric property and does not account for what material the arms are made from. Now, when you factor in the material properties of what the arms are made from you can see that the yield strength of 1018-1020 cold rolled steel is over twice the yield strength of our competition's material. For simplification to figure out which one is the strongest let's assume each control from each company is the same length and has the same end configuration. This will simplify things a little bit. So now we can compare apples to apples and figure out which control arm can carry the largest bending load.
stress = MC/I. For now we will consider the stress level to be the yield strength of the material since any stress above the yield strength will allow the arm to bend. M since we said each arm is the same length will simply be the bending Force (F) times a constant which we can throw out for comparison sakes. C for will have a specific value for each cross section and I will be as stated above for each material.
1.75" Solid Cold Rolled Steel
76,000 pounds = F * .875/.460 therefore F = 76,000*.460/.875 = 39954 pounds
2.00" Solid Cold Rolled Steel
76,000 pounds = F * 1.000/.785 therefore F = 76,000*785/1.000 = 59660 pounds
2" Diameter 1/4" Wall Low Carbon DOM Tubing
let's assume the highest yield stress of 34,800 pounds
34,800 pounds = F *1/.537 therefore F = 34,800*.537/1 = 18688 pounds
2" x 2" 1/4" Wall Low Carbon ERW Tubing
let's assume the highest yield stress of 34,800 pounds
34,800 pounds = F *1/.908 therefore F = 34,800*.908/1 = 31598 pounds
This means that 1.75" Solid Cold Rolled Steel can take the highest load of any material commonly used by manufacturer's today. That is a Rock Krawler Advantage.
What are Rock Krawler's control arms made of?
All of our " Long" lower control arms are 1.75" or 2.00" diameter solid 1018-1020 cold rolled steel. Each control arm is drilled and tapped versus having a bung welded into it for a joint. This yields a much simpler arm with one less step. Simpler is Better! That is a Rock Krawler Advantage.
How come on some of the triangulated 4 link systems Rock Krawler has use the stock upper control arm mounts? Wouldn't that make it function like a short arm system?
On some systems we do use the stock upper mounts to locate our rear triangulation members. Some we do not. We try to do what is best for the particular application and the end consumer. On the systems that we use the stock upper mounts for our triangulation member for example our TJ 5.5" X Factor Long Arm System here is why we do it; first of all the upper arms are raised up and go above the differential. This levels out the upper control arms in the horizontal plane while the long lower control arms are still at a downward angle. What this does as the axle goes into a full droop condition is since the lower control arms are pulling away at a larger angle than the top control arms the pinion angle does not go into a binding condition. As far as articulation is concerned our triangulated 4 link conversion has no binding conditions up until the joints run out of movement which is +/- 30 degrees. That is a ton of wheel movement. Another benefit is we can bend the uppers so they clear the factory exhaust routing so you do not have to replace the exhaust system which on TJ's is stainless steel from the factory. In our triangulated systems where we use the factory mounts we also give reinforcing mounts to ensure they are extremely robust. In other instances where we had to use longer rear uppers do to pinion angle changes or whatever, then cat back exhaust modifications will of course be required. We feel the benefits of being able to maintain a factory exhaust or readily available performance aftermarket exhaust system far out weigh the longer rear upper links. If it robbed the vehicle of performance we would not do it!
Can you safely weld to a unibody vehicle?
First off, the factory welds all of the OEM brackets on to the frame so why can't you? Welding is much more structural than conventional fastening with hardware. You do not have to worry about drilling holes or bolts coming loose. Where all of our long arm brackets weld to the unibody frame, the frame is actually double or triple wall thick to ensure a good weld is possible. We also spec out stitch welding which has less heat build up than full seam welding and better stress distribution.
How strong are Krawler Rod Ends?
All of our Krawler Rod Ends are rated for 55,000 + lbs. +/- 30 degrees of misalignment. They have a Teflon liner for maintenance free use.
How strong are the Krawler Joints?
All of our Krawler Joints are rated for 60,000 to 65,000 + lbs. radial load with +/- 20 degrees of misalignment. They are rebuildable and serviceable for extended usage.
How does Rock Krawler's X Factor long arm brackets mount for the long arm systems?
All mounting brackets are made of 1/4" thick steel that has been laser cut to guarantee accuracy. The long arm brackets mount to OEM skid plate or cross member mounting bolts. This ensures you that the brackets are in the proper location which guarantees the assembly is done correctly.
Can Rock Krawler systems be used for other applications or types of driving other than Rock Crawling?
Absolutely, the biggest difference in setting up one of our systems for anything other than rock crawling is the shock specs. Our shocks are spec 'd for rock crawling. By that we mean we give as little compression as possible which gives the most stability for rock crawling. All of our systems will function great in other environments, but we do recommend ordering the systems without our shocks and finding shocks that will function well for your intended usage.
If you have any questions; comments or concerns not addressed on this page feel free to contact us and we will be more than happy to help you.
All content including text and photos © Rock Krawler Suspension, Inc. 2005
© 2005 ROCKKRAWLER.COM
ahah!! a search of the forums will work. i remembered this was written up once and i thought i could bring it back. you know, beat the dead horse a little more... haha
but i have been looking through the internet for good examples of well built rear long arm/coil over suspension setups OVER 5 INCHES! im just tired of scrolling through thousands of procrap kits for looks. i have the front (for the better part of my idea) figured out.
but i dont like the small amount of flex that leaf springs offer on full size trucks when paired with front spring setups...
counterpoint anyone?
i am pretty mathematically inclined, so i dont think i will have a problem understanding it, ... once, i , .. understand it...?
but figuring out how to "use" some of the 3 / 4 link calculators...
they all call things different names
ANGLER!!
if you dont mind, if you could just let me know when you are going to be doing yours so that maybe i could sit-in/help-out, id appreciate it...
I used to have a 4 link calculator on my computer somewhere. I'll search for it. It even had the instructions for how to use it. If I can't there are many out there. First you better learn how to weld and get a garage, if you do it during the winter months.
hey, if you can weld, then i feel pretty confident. and i think i have a garage to use somewhere in the northpole vacinity :whistle:
i just dont like going there cause the owner is STINGY about the beer
:lol:
i can weld, just not very well