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Discussion Starter #1 (Edited)
I am working on a double triangulated 4 link system on a 2.5 ton rockwell. The top links are mounted on top of the axle at the outer most point without interfering with the airbag, triangulating to a crossmember between the frame rails just in back of the transfer case. The separation between the mounts on the axle end are 31" and the separation between the mounts on the frame end are 13". The lower links (if you want to call them that) are mounted on a tube that is mounted on the front side of the axle and at the centerline and triangulate to the inside of the frame rails. The separation between the mounts at the axle are 4" and the separation on the frame end is 29". The upper links are 67" long and the lower links are 54" long. Everything says the lowers should be longer than the uppers (will this work). I put all the numbers into the 4 link analyzer and it comes out with 112% anti squat, .15" oversteer and 4 degrees of oversteer. We are using airbags for the suspension mounted outside the frame rails and to the top of the axle. Does it sound like this setup will work?? It is different from all the setups that I normally see but I didn't want to build a big box on top of the axle and put the mounts on top and loose all that space ( I wanted to tuck the axle right up under the vehicle).. Any feed back on why this setup will work or not work..

I might be able to post the mock up pics of the suspension tomorrow (they might help to answer some questions if the write up is not clear).

I tried to attach some photos but it said they were to large, if anyone would like to attach some photos for me I can email them to you. I don't know how to make them smaller.. Thanks
 

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Discussion Starter #2
Anybody any thoughts, it would not let me attach photos, it said they were to large. I can email if anyone will post up for me..
 

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When you say the links have 4 inches of seperation at the axle do you mean vertically? If so that is not very much vertical seperation and may cause problems with leverage on link ends and brackets as well as your links may make contact during full articulation resulting in binding ..A good rule of thumb is 6-8 inches at the axle and 2/3 of that at the frame end..Remember I said a "general" rule of thumb that is not set in stone..Post some pics if you can. Also, there is an old thread that I can't remember the name of at this time (NOT THE GOD OF SUSPENSION thread) that has some good real world discussion. You can probably find it by searching the username Frankie Fountain. Probably around the early part of 2003 or latter part of 2002.There is some discussion regarding the longer upper vs longer lowers in this particular thread...
 

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If I understand you correctly then I built a very similar suspension:



The problem is the roll axis has a very steep angle and a low roll center. It causes a lot of body roll and shifts the axle sideways during articulation.

I rebuilt the suspensions and ended up with this:

 

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Nice setup you have there!!
 

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Discussion Starter #7
Here are some photos, I had to change the size so I hope you can make them out.

I could not find the thread by searching by frankie fountain, but I appreciate the help (onetonwillysands10).

CJ Lagos it looks that both your links terminated at the frame (the same idea as mine but then again different). Look at my pics and see if you think I will have the same problems or if you think it might work. I appreciate your assistance also.

I appreciate people trying to help others out
 

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I will see if I can find that thread for you. I have printed off out in the shop. It appears that your links have more than 4 inches of vertical seperation;but, after seeing your link set-up and reading CJ Lagos post I don't think that was what you were asking about..Looks pretty good...at least what I could see with those oversize pictures.
 

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wiringnatzi,

Even though my uppers were parallel and yours are triangulated, the basic geometry is the same and the calculations for roll axis and roll center are almost identical. There is a reason you don't see many people running this suspension.

CJ
 

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Discussion Starter #10
Thank you guys,

CJ Lagos, what are the lengths of your links now?? You really have me rethinking the setup.. I think I'm going to change it and take some more photos on Monday..
 

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I sold that Jeep and don't remember the arm lengths. You want a flat roll axis and a high roll center...the best way to do it is with a double triangulated setup...like yours but opposite(lowers converge at the frame, wide on axle and uppers converge on top of the axle and wide at frame). Imagine the lowers are infinitately long and where they will intersect. With the setup I just described the "instant center" will be slightly behind and above the frame lower arm mounts. The upper arms instant center will be in front of and slightly below the axle upper arm mounts. Now draw a line connecting these two instant centers and that is the roll axis. Where this line crosses axle centerline is the roll center(in this case it cross axle centerline up near the upper control arm mounts). It's possible to build the suspension using 4-link analyzer by Triaged and get the roll axis perflectly flat. A tire droops perpendicular to the roll axis, so if the axis is flat the tire will go straight down, if it is angled the tire will move backwards as it goes down giving you "rear steer".

Go through the same steps for your suspension you'll find that he roll axis is extremely angled(since the lowers IC is below axle centerline) and the roll axis is very low.

Hope this helps,

CJ
 
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