Not your mama's long arm debate

Chris said:
Blaine is a designer of off-road suspension, so while I always wish he would do something like this, he's publicly mentioned why he won't on numerous occasions, so that's a dead end outlet.

I agree though, if it could be a Wiki format (or at least a thread where everyone could edit the original post), I think maybe people would contribute, I don't know.

I'm sure I could piece together information from books about off-road suspension design and setup, but I'm not sure how well a book about general off-road suspension design is going to apply to the TJ platform.
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And this right here is EXACTLY what I want to try to pound out.

I feel that such a reference would be maximally helpful if it started with the basics of what all of these geometry terms mean, and then progressed into how they apply specifically to a TJ. For that we need guys with tons of TJ knowledge. I've owned a couple, but I haven't seen it all. And my knowledge is spread much more thin across many platforms. Trying to convince some of our experts to contribute to this kind of reference is key. Even if 'contribute' means post snarky comments correcting us where we are wrong so we can fix it. Even if annoying, it would eventually get us there.
 
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greaseorbounce said:
And this right here is EXACTLY what I want to try to pound out.

I feel that such a reference would be maximally helpful if it started with the basics of what all of these geometry terms mean, and then progressed into how they apply specifically to a TJ. For that we need guys with tons of TJ knowledge. I've owned a couple, but I haven't seen it all. And my knowledge is spread much more thin across many platforms. Trying to convince some of our experts to contribute to this kind of reference is key. Even if 'contribute' means post snarky comments correcting us where we are wrong so we can fix it. Even if annoying, it would eventually get us there.
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I think you'll find a single-source article made by an "expert" will be riddled with preference and opinion. That's all experience is with a thing like building Jeeps.

For instance, I can't believe people like their short arms on 4 inch springs. For me, that combo handles awful off road. And when I still spot those guys, I'm like "Here's the line, but be careful, don't roll over." :D
 
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pcoplin said:
I think you'll find a single-source article made by an "expert" will be riddled with preference and opinion. That's all experience is with a thing like building Jeeps.

For instance, I can't believe people like their short arms on 4 inch springs. For me, that combo handles awful off road. And when I still spot those guys, I'm like "Here's the line, but be careful, don't roll over." :D
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I want you to build my mid arm suspension. 🤭👊
 
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pcoplin said:
I think you'll find a single-source article made by an "expert" will be riddled with preference and opinion. That's all experience is with a thing like building Jeeps.

For instance, I can't believe people like their short arms on 4 inch springs. For me, that combo handles awful off road. And when I still spot those guys, I'm like "Here's the line, but be careful, don't roll over." :D
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I don't like my 4" springs on short arms, but it is what I have right now. There is room for improvement even with short arms. Moving the LCA on the stock frame and axle mounts and adding taller UCA axle mounts with extra holes gives the ability to get rid of high AS with short arms.

The only things I have seen posted on rear IC is about 95" to 125" long and 33" to 36" high. Playing with numbers I have trouble getting the IC that long without moving the UCA frame or axle mount about .250", which would be a pain. I have not really seen much about making short arms better either. I estimated the "x" value and will get the correct number soon.

Here is a shot of the Triaged calculator. The first group of numbers is the best I can do with the current mounting points. The second is lowering the UCA axle mount .250".

1585730148678.png
 
that's exactly how you control this^. you have to manipulate those connection points to come up with the design.

the trick is having the knowledge to know what you need to build.
the manipulation of the links on paper is easy, but the point you pick needs to have an educated reason or it's like tossing a dart in the dark. and that's gonna be based on primary usage.

you got about a 5" separation on the frame and a hair over 7" at the axle? are those #'s correct? i thought the TJ had about 8" at the axle end.

i've not found a calc that plots for me so COG unless pinpointed leaves us using this tool as nothing more than a ballpark guide/guesstimater.

i'll post some links i've found.

http://www.orcfab.com/tech/4link1.html
https://www.fourwheeler.com/how-to/0909or-front-suspension-technology-link-basics-part-2/
https://www.barnes4wd.com/Installation-Tips-for-Adding-a-Three-Link-Suspension_b_8.html
i've seen Nate . he talk a lot of game but ignores what he teaches. but i don't disagree with everything he says
i've seen Burkey, so i won't post that either. but same here, i don't disagree with everything he says.

my best advice if you wanna mess with this stuff is to learn to understand how AS and AD effect the rig and how to control the placement of the IC.
open a calc plot your current set-up and then plot an opposite set-up. play with the link connection points and you'll quickly see the effects through the calculations.

the last line in Brians post is exactly why bolt on sucks.
 
Brianj5600 said:
@someguysjeep Thanks for your reply. I read through your build and it is impressive. What type of wheeling are you building for? What are you shooting for as far as AS and IC and how did you decide on the numbers?
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i wanna take it to play on the rocks out west. i want a decent all around performance with good ability to climb.

and i'll be the 1st guy to tell you not to do what i've done the way i've gone about it.
my build has become a hodgepodge of i better learn this or i'm F'd. knowing full well more rework is ahead.
and getting into things i don't have to do, just cause i wanna try it. i wanna need the mods i'm doing so it gives me incentive to push to visit places i can/will need them.

my "right now" requirements are to get it mobile and road safe enough to not endanger me or anybody else.
1st is get it to the DMV emissions check, so i can get it plated for 2 more yrs b4 next inspection, which it will not pass.
2nd the front axle is new and the gears need broken. should it be road worthy i'll do that.
then i'm ripping the whole back end apart to raise and tuck the frame for CO's or additional struts, push the axle back and triangulate the links.
the new wheel base will require a complete remapping and guestimation of where i can plant theses points.

the IC, i want lower than what i can get from a SA, but i don't need it under my ass either. for the front axle my intention was to lower the IC from what the SA generated, while trying to maintain a fair amount of the AD. and be able to fit it under the rig.

deciding on the #'s, here's where opinion gets involved. pick a spot you think is correct based on an educated guess or ask for advice.
a functional sys is the goal, beyond that.......without significant testing, a horrible result or failure to perform, your not aware of what could have been left on the table as far as is this PERFECT. we are already groomed to expect some compromise.

again i'm no expert on crap. i can move the twigs and plot the points, to compound the design add roll center to this, the IC's you create effect this. i don't have the perfect set up pre-designed.
and if i misspeak i fully expect someone to post up and set me right.
 
xxdabroxx said:
Does anyone have stock and 4" lift tj suspension plugged into the calculator?
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i'd suspect a plotted bone stock factory suspension is the best we could ask for. for anything else to be accurate you would really have to nail your COG, which is different for us all based on load and weight distribution.
 
Question. ;)

Are these AS calculations being made on flat ground?
 
jjvw said:
If you look in the other big long arm thread from a couple years ago, I posted these.
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if you could pick and ideal AD range for the front end for what you wheel, what would you shoot for?

i can nail any point it's just whats gonna be more optimal. 70-90 up front, 90-110, 100-120 whats a good zone to start at? this is the experience/knowledge i lack.
and i know shocks effect AD to some degree too as well as the struts i'll run can actually have adjustable stiffness. how much additional AD could the shock supply, or is that negligible?
 
someguysjeep said:
if you could pick and ideal AD range for the front end for what you wheel, what would you shoot for?

i can nail any point it's just whats gonna be more optimal. 70-90 up front, 90-110, 100-120 whats a good zone to start at? this is the experience/knowledge i lack.
and i know shocks effect AD to some degree too as well as the struts i'll run can actually have adjustable stiffness. how much additional AD could the shock supply, or is that negligible?
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I went with whatever the Savvy kit creates, which puts the front arms pretty close to parallel to preserve caster throughout the travel. That seems to be a different focus than looking strictly at AD.
 
jjvw said:
I went with whatever the Savvy kit creates, which puts the front arms pretty close to parallel to preserve caster throughout the travel. That seems to be a different focus than looking strictly at AD.
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ok, i kinda remember us coming around to that once b4.
 
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