School me on mid-arm vs long-arm

mrblaine said:
What do longer arms do for you? You are coming at it from the direction that one needs a longer arm equivalent to the length commonly used on a long arm kit. Why do you think you need an arm that long?
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I am actually coming at it from a different direction altogether. I am working the 4-link calculator and trying to get the anti-squat to be as close to 100% as possible. I know that this is a single metric and perhaps not the holy grail but I am focused on it the most because it appears to be the metric that I can change the easiest. That being said, my axle mounting points are fixed. I have committed myself to 37" tires and I have 4.5" springs. The CG Height is what it is (assuming around 34" for my TJ) and that leaves placement of the frame side mounts as the only variables. So the longer the arms, the closer I get to 100%. Shorter arms yield me a higher percentage. So in a nutshell, that's why I'm advocating for longer arms. But I'm definitely not a suspension expert and am trying to get an answer as to why I might prefer a shorter arm. For example, I could see that have shorter lowers keeps the links out of the rocks and shorter uppers might triangulate the axle a little better and prevent it from wandering at higher speeds?
 
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Jerry Bransford said:
My former long arm suspension was absolutely superb at just one thing..., getting constantly hung up on the rocks.
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OK, clarify. How long were your arms? 4 link or 5 link? Trailered or street driven? So are you saying that you no longer get hung up on rocks because your links are more vertical and out of the way? Throw me a bone here....
 
Jerry Bransford said:
My former long arm suspension was absolutely superb at just one thing..., getting constantly hung up on the rocks.
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How does the 4 link calculator account for dynamic movement and steep climbs where the poor behaviors of lifted short arms start to manifest themselves?

Again, what behavioral problems are you trying to solve?
 
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toximus said:
View attachment 158393
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toximus said:
This seems to have traded the problem of clearance for the problem of not allowing for much up travel.
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Well seeing as folks are just responding with pictures and not data/words, what's the difference? A picture of a stuck jeep tells me nothing. A picture of a jeep that is not stuck tells me the same. Not trying to be a dick here but we are on page two and nobody has responded to a single question that I have asked :rolleyes:. Now I already know that Savvy is the best and that long arms suck but I can't find out what everyone considers a "long-arm" and why a 27" rear LCA is the best.
 
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jjvw said:
How does the 4 link calculator account for dynamic movement and steep climbs where the poor behaviors of lifted short arms start to manifest themselves?

Again, what behavioral problems are you trying to solve?
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Right.....now we are talking. Lifted short arms ARE a problem. At least in the front......I am not 100% sure about the rear. So the question is HOW much longer should the arms be before they start getting too long. And if you ignore the calculators, what are you relying on? Trial and error? Are you guys going out with different length arms and swapping them out until you get the perfect length? Something that climbs well and also does well going 70mph down the road/through the desert.
 
Rock Toy said:
Right.....now we are talking. Lifted short arms ARE a problem. At least in the front......I am not 100% sure about the rear. So the question is HOW much longer should the arms be before they start getting too long. And if you ignore the calculators, what are you relying on? Trial and error? Are you guys going out with different length arms and swapping them out until you get the perfect length? Something that climbs well and also does well going 70mph down the road/through the desert.
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What is the problem with the front? Understand that your answer (and I know what it will be) is going to tell us where you are in your understanding of all of this.
 
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Short arms and tall tires don't work well together. Your starting point is a pretty vertical upper and lower control arm that wants to wants to fight obstacles instead of riding over them. And on the road.....well, a rough ride. But I'm not researching front suspensions at the moment. I am looking for answers about the rear suspension and most specifically, about why Savvy designed the length of their arms at around 27"s. I am NOT attacking them and I am not pretending to know more that you or anyone else on here. Just answer some of my questions. Or don't. But whatever you do, please don't answer my questions with more questions. Seems to be a thing around here..
 
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Rock Toy said:
.... But whatever you do, please don't answer my questions with more questions. Seems to be a thing around here..
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You know what an instant center is. What behavior in the rear suspension is encouraged when it is high? When it is low?
 
This isn't what the OP is asking about but the Nth Degree arms are inside the frame rails and it has a lot more than 2" of up travel.
Daryl point is that NOT all longarm kits got hung up on the rocks like the Rubicon Express. We all know Jerry's infamous picture.
 
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Rock Toy said:
Not trying to be a dick here but we are on page two and nobody has responded to a single question that I have asked :rolleyes:
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Welcome to my world. Questions are answered with questions.

Blackjack said:
There is a good amount of info in several threads including talk about roll centers. Jeep West is following a similar recipe that Nth Degree did in regards to roll centers. He lowers the front because he is adding a drop pitman a lot of the time and raising the axle side of the panhard bar is more difficult compared to lowering the frame side. He also is going with bushings in a double shear mount for strength and allows him to push the axle forward a small amount if he so chooses. The high roll center in the rear does make for more stability off camber but at the expense of adding more bind into the suspension overall.
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In the last year I have looked through many many pictures on the Jeep West FB page trying to focusing on the TJ stuff. I noticed a dropped pitman arm and lower frame side TB mount and stock axle mount on one build. I don't know if the pitman arm was a reaction to the lower TB mount or the other way around.

Blackjack said:
Savvys approach is all about gaining performance with a minor sacrifice in rear roll center. The front is not changed because they want the axle in the stock location as close as possible and at 4 inches of lift a good panhard bar and steering linkage will perform just fine. As Blaine has mentioned a few times the lower roll center in the rear can be made up for with well tuned outboard mounted shocks and good sway bars. This allows less bind in the rear suspension and predictable manners in certain climbs where "jacking" may occur.
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I understand that good shocks can help on off camber sections, but it seems like shocks can only slow body roll and not limit it.

JeepWest posted a video of a SA TJ doing what normally will cause the drivers front to lift even roll in a parking lot. A few times it lifts the rear tire, which means there is a lot of rear roll resistance cause by high rear roll center? Is this evidence of geometry that eliminates jacking?


https://www.facebook.com/video.php?v=1159205487545140

Blackjack said:
You also need to look at where Dave and Blaine wheel at a lot and that will also help understand their approaches. If you spend any time in the Tillamook area of OR you will understand a lot of what Dave does. Tractionless and off camber is the name of the game. Blaine spends a lot of time in JV and has a lot more short vertical climbs and sharp ledges to negotiate. Neither approach is wrong, they are just different solutions to a particular set of criteria.
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The places I wheel are somewhere in between. Our hills can seep water for days after a good rain keeping some obstacles slippery.
 
mrblaine said:
That is all very correct except for one minor thing. This is very common in JV-
View attachment 158310

We absolutely need off camber stability out there.
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True but I bet you were looking for less torque reaction from the chassis where if you are at Browns Camp you are worried about slipping on a greasy hill and hitting a rut.
 
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