My 4 Link Calculations (need some opinions)

wheelNC94GC

wheelNC94GC

Well-Known Member
Joined
May 19, 2007
Location
Chesnee SC
Ok this is my first time attempting to fab my own long arms...I realize its not going to be perfect maybe not even close I'm still trying to understand everything. These are the numbers and lengths that I have come up for the first set of calculations. What do you guys think? What can improve and how?
4_Link_Details.jpg

4_Link_side.jpg

4_Link_Top.jpg


One reason i did the single triangulated was because i was affraid of the arms hitting each other when at full flex and then the suspension binding up. Also this way i don't have to build some sort of rear crossmember. But, if I have to, to get the numbers I need I will. For the record I've got a 94 zj...i'll be running 37-38's, have about 9" of lift, running a fullwidth hp44 front, and 14B SHAVED rear. I would get a 60 but thats just not in the budget right now. The type terrain i want to be abel to wheel is for example like tellicos tougher trails like schoolbus, upper and lower, etc.

I know every long arm set-up is different so i tried to include as much information need sorry if its to specific of a question just let me know what you guys think. Thanks

Brandon
 
i'm stoopid and can't help.

but i am curious what calculator that is...

:)

-Erik
 
I'm not great with the link calculator yet, but just judging from the kinds of 4links I've seen your lowers look like they could go longer. I'm doing a dual triangulated setup on mine and my lowers will be just over 5ft long while yours are less than 3, granted its a shorter wheel base but not by that much. are the lowers angled in slightly like that due to the width of the 14B relative to your frame? I'm assuming you're going to mount the frame end of the lowers directly under the frame.

If you do straight lowers it tends to rear steer when flexed, and with short lowers that problem will be more amplified I would guess.

theres lots of threads like this on pirate, enough for HOURS of reading.


link to the calculator: http://www.pirate4x4.com/forum/showthread.php?t=204893
 
Erik said:
i'm stoopid and can't help.
but i am curious what calculator that is...
:)
-Erik
Click to expand...
Haha I dont consider myself smart at all. I got the calculator off of pirate but I don't remember exactly where. If you would like the files for it just e-mail me and I'll e-mail the zip folder for you...or aim works too.
 
jmg4runner said:
I'm not great with the link calculator yet, but just judging from the kinds of 4links I've seen your lowers look like they could go longer. I'm doing a dual triangulated setup on mine and my lowers will be just over 5ft long while yours are less than 3, granted its a shorter wheel base but not by that much. are the lowers angled in slightly like that due to the width of the 14B relative to your frame? I'm assuming you're going to mount the frame end of the lowers directly under the frame.

If you do straight lowers it tends to rear steer when flexed

theres lots of threads like this on pirate, enough for HOURS of reading.
Click to expand...
The LCA's are angled outward at the axle like that because it brings my oversteer angle down. Yes they are going to be mounted directly under the frame rails...the arms can be longer without affecting these numbers very much. But, I was trying to keep the lowers shorter than the uppers so when the axle droops the pinion angle will rotate up and stay pointed toward the TC keeping the angle good to prevent binding. Also the gets the angle between the upper and lower closer to the 40deg. mark...i dont know the angle exactly but it's going to be hard to get a 40deg. angle with the upper/lower arms under a zj as far as mounting points go.

Ya i've been reading for DAYS haha its driving me crazy. How bad do you think 3 deg. of roll oversteer will be?
 
Every thread I read has a different opinion of whats good, acceptable, bad. Some people say they have "terrible" numbers but they work fine out on the trail and off the web-wheeling discussion boards. My upcoming 4link will be my first, maybe some more experienced builders can chime in.
 
Grab the newer version.. it allows you to see how things change as you go through droop and compression. I think it's called v3-1.1c (with travel updated)

$5 says as you go through even 4" of compression and 4" of droop, you're going to see radical changes that aren't good.

A few other items.. your CG is probably about 18" or so too low, 38's aren't 38" tall, and no tire has a rolling radius near half the height. My 42's are 41" tall and have a rolling radius (aired down) of 18.5".

Oh, and save yourself a headache.. work in 1/2" (or even 1/4" if you must) increments.. ;)

It's a good tool once you understand the fundamentals, but you want to make sure that a: it'll all fit on the vehicle, and b: it stays as consistent as possible through its travel.
 
Rich said:
Grab the newer version.. it allows you to see how things change as you go through droop and compression. I think it's called v3-1.1c (with travel updated)
$5 says as you go through even 4" of compression and 4" of droop, you're going to see radical changes that aren't good.
A few other items.. your CG is probably about 18" or so too low, 38's aren't 38" tall, and no tire has a rolling radius near half the height. My 42's are 41" tall and have a rolling radius (aired down) of 18.5".
Oh, and save yourself a headache.. work in 1/2" (or even 1/4" if you must) increments.. ;)
It's a good tool once you understand the fundamentals, but you want to make sure that a: it'll all fit on the vehicle, and b: it stays as consistent as possible through its travel.
Click to expand...
Ya i do have the version that tells me the travel and all that...you nailed it though it does change alot in anti-squat from normal to full droop. Could you explain the rolling radius alittle bit more? The 38's have a OD of 37.8 so would you not just half that for the radius? Like i said i'm still learning so sorry if this is a dumb question.
 
well it theory that would be right, with no weight on htem... but once you load them down, and air them down... the rolling radius is ~40% of the height of the tire, depending on all conditions of course....
 
Ok here is a "revised" version. I've got fairly consistant numbers from 4" compress to 4" droop. Let me know if this seems to be alittle better. I took some advice from you all (thanks by the way).
ai215.photobucket.com_albums_cc27_fmtndrummer_DT_4_Link_Details.jpg

ai215.photobucket.com_albums_cc27_fmtndrummer_DT_4_Link_Side.jpg

ai215.photobucket.com_albums_cc27_fmtndrummer_Double_Tri_4_Link_Specs.jpg
 
your gonna want to get that antisquat lower more the likely... youll want the rear to squat some under throttle, or it might try to just hump the rock instead of climbing over it...
 
paradisePWoffrd said:
your gonna want to get that antisquat lower more the likely... youll want the rear to squat some under throttle, or it might try to just hump the rock instead of climbing over it...
Click to expand...
Any suggestions on a good number? I just re-did a few things and its basically the same numbers and the AS at compressed is about 85% and at droop it is about 67&. In the "GEOMETRY SUMMARY" up top (on the main page) the anit squat is 83% and the Roll Axis Angle is at 0 deg.
 
try getting the instant center out in front of the rig more if you can.. and shortening the upper link some will typically allow you to have more separation at the frame, which makes for less AS..
 
more seperation at the frame end will help antisquat as well as lowering the heigh of the frame mount (which might not be possible)... what the magic number is i dunno, but id think in the mid to low 70s... try to get that AS line closer to the top of the front tire, as well as the instant center farther forward... might try making the links parallel horizontally..
 
paradisePWoffrd said:
more seperation at the frame end will help antisquat as well as lowering the heigh of the frame mount (which might not be possible)... what the magic number is i dunno, but id think in the mid to low 70s... try to get that AS line closer to the top of the front tire, as well as the instant center farther forward... might try making the links parallel horizontally..
Click to expand...
Thanks ALOT for all the help I appreciate it. I finally got the AS down to 71% there is like a 2 degree roll axis angle but i think i'll be able to deal with that. The instant center is at the top of the front wheel in the center as well as the AS line. I think i'm ready to start building it up after a few more minor adjustments. But once again thanks i'll be starting a build thread on here very soon i think so i'll keep you guys updated.
 
everytime i think of doing a 4-link setup, i look at one of these threads and start wandering off to la la land...

one day i'll get the hang of it...

good luck on the build.
 
There's a bunch of photos in my build thread..

"Just some junk on Rockwells" in the truck gallery..
 
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