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Old 07-17-2001, 01:25 AM   #1 (permalink)
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Post THE GOD OF SUSPENSION...[for those of you who don't know]

For those of you who really don’t understand what your talking about when it comes to designing a link type suspension let me fill you in on a lot of stuff. First when designing a link type suspension for off-road use you must consider: Anti-Squat, Roll axis, Link length, and Link angle.
Anti-Squat is a property that determiners how much the rear will raise or lower when accelerating. This is the reason a mildly modified Wrangler with leaf springs climbed the (A-7) obsticle that the Scorpion could not at the last ARCA event in Cedar city. With a large percentage of Anti-Squat the rear end of the vehicle will lift under acceleration. In the case of the Scorpion this causes the rear end to try to drive forward under the vehicle while the vehicle remains still. The result is the vehicle develops a condition similar to axle-wrap. The rear end starts to hop causing a decrease in traction.

Link angle is directly correlated to Anti-Squat characteristics. The steeper the angle of the links (assuming they are parallel) the greater the Anti-Squat. There are ways to combat this.

A longer Link length doesn’t necessarily mean a less steep angle. Also a longer link doesn’t always mean less rear steer. Rear steer is a property that is determined by roll-axis. Many of you are not even considering this when talking about link design. This is one of the most important considerations. Also when making links longer there are considerations such as bending moments, Euler’s Coulomb Buckling Theory, and break over angle (High Centering).

Many of you have commented on how a link type rear is not good since it reduces the amount of front flex by making the rear flex more. This is not true. If the suspension is properly set up the amount of flex for both axles will remain the same.

Before talking about or building a link type suspension, figure out what you need to know, or ask someone who does. It will make you look a lot smarter and you will be much happier with the results.

Now let the smack talkin begin !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!


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Old 07-17-2001, 01:43 AM   #2 (permalink)
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I would think on a rockcrawling rig one would want very little anti-squat. Correct me if I'm Wrong but in a link type suspension the amount of anti-squat is detirmined by the angle of the links ie more angle more resistance to squat so to speak. any opionions All Mighty God of Suspension?
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Old 07-17-2001, 05:18 AM   #3 (permalink)
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FYI - I have no clue who you are, what you just posted could have easily been cut & pasted from any suspension design manual, and what you just posted is not very impressive either (and I don't even know that much about link suspensions).

On the whole - I haven't seen anything here that makes you look like some suspension "god", so if you plan to post to impress - pull out the bigger guns <IMG SRC="smilies/rolleyes.gif" border="0">
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Old 07-17-2001, 06:51 AM   #4 (permalink)
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(pic's at the bottom)

apparently your opinion of a god is lower than mine.

i have a well balanced rig front to rear, it has a rear 1/4 elliptic 4 link and also a front 5 link. so yes a link type susp. can be well balanced.

i know where my CG. is, i know the height of my roll center, my anti-squat is dead on with the weight, wheel base, and center of gravity, i have less than 2 inches of rear steer at full droop measured on the vertical plane.

so i'm very happy with it.

i don't think your going to tell me anything that i haven't already forgotten.

at least i havent seen anything that you have posted that has impressed me yet, but please keep trying.

and i'm nowere near a god at anything.
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<IMG width=416 height=312 SRC="http://www.pirate4x4.com/ubb/uploads/rsusp1.JPG">

<IMG width=416 height=312 SRC="http://www.pirate4x4.com/ubb/uploads/rsusp2.JPG">

<IMG width=416 height=312 SRC="http://www.pirate4x4.com/ubb/uploads/rsusp3.JPG">

<IMG width=416 height=312 SRC="http://www.pirate4x4.com/ubb/uploads/rsusp4.JPG">

<IMG width=416 height=312 SRC="http://www.pirate4x4.com/ubb/uploads/rsusp5.JPG">

<IMG width=416 height=312 SRC="http://www.pirate4x4.com/ubb/uploads/rsusp6.JPG">

<IMG width=416 height=312 SRC="http://www.pirate4x4.com/ubb/uploads/rsusp7.JPG">
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Old 07-17-2001, 09:21 AM   #5 (permalink)
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I think anti-squat is GOOD when run with a center limiting strap.
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Old 07-17-2001, 10:26 AM   #6 (permalink)
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<STRONG>I would think on a rockcrawling rig one would want very little anti-squat.</STRONG>
Depends... you going uphill or downhill?

There's no single answer to all of these things, and they interrelate with complexity. I've seen video of a high-travel rig travel into apparent squat on one side of the flexed-out rear suspension, and anti-squat on the other side. Every time he fanned the gas, the whole rig wanted to roll itself. Ooops!

Experimentation is fun, but most home-brewed multi-link suspensions don't seem to have solutions that allow safe on-road handling... they make too many compromises in favor of off-road performance.

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Old 07-17-2001, 11:12 AM   #7 (permalink)
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Calpoly..

You have stated some good points on
Design principals, but nothing that you couldn't find at local book store...

To truely become a "GOD" you must be able to turn "Principals" into reality...SO just how many linked rigs have you made? and please post pics...

Please understand that going to school and the real world are different...

I speak from exp. former "ASU GUY"
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Old 07-17-2001, 11:14 AM   #8 (permalink)
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Quote:
Originally posted by Tin Bender:
<STRONG>

I speak from exp. former "ASU GUY"</STRONG>
Damn i almost went there, thank god i did not <IMG SRC="smilies/biggrin.gif" border="0">
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Old 07-17-2001, 11:14 AM   #9 (permalink)
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And if CALPOLYPUD=BRIAN then <IMG SRC="smilies/thefinger.gif" border="0"> <IMG SRC="smilies/skull.gif" border="0">
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Old 07-17-2001, 11:16 AM   #10 (permalink)
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lemme guess WEll Done Man Chico?..
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Old 07-17-2001, 11:19 AM   #11 (permalink)
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actualyl he is a drop out, local jc student turned sequoia now computer dork/mechanic to all friends! he he, jiMMy
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Old 07-17-2001, 11:21 AM   #12 (permalink)
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A little Anti-Squat is good because it increases the force placed on the tire. This is createtd by a link setup in which the vector sum of the forces in the verticle plane are pointed toward the ground. In the case of two parrallel links parallel with the ground, when the vehichle is at ride hight there is no anti-squat caused by the links. Intertia of the center of gravity will actually cause the rear to squat in this particular case, as the vehicle accelerates. Of course this is only true if the center of gravity (CG from now on)is above the roll ceter of the vehichle. On almost all offroad vehichles the CG will be higher than the roll center. So what we really want is a susupension that combats the squat caused by acceleration and provides a small amount of downward force to increase grip. On vehicles with large link angles in the rear the anti squat will be very high. What this means to rock crawlers is get your links as flat as possible. This is my general reccomendation although there are ways to run larger angles and still accomplish the same task.

For Dr.Mud If you believe that this is a cut and paste ask me a more general question and you will see where the knowledge is coming from! The Big Guns are Drawn!!!!!!!!!!!!!!

Steelman, Your Bronco does appear to be well balanced and the rear suspension does have very little rear steer. I see a little more in the front though. Your getting close! The front does not matter as much though because you can combat the link sterring effect with the steering wheel. The only real problem is the fender rub cause by this.

Ant, the center limiting strap only limits how far the rear axle will move it has nothing to do with anti-squat.

randii, You are correct, very little anti-squat is desireable. In either case up or downhill you do not want much. In the case of downhill it is not such an issue since forward acceleration is what cause anti-squat. In most cases you are decelerating and this would actually lend to squating in the rear. This is good because it combats the tendency for the vehichle roll forward which is caused by the center of gravity being higher than the roll center.

Keep the questions coming! The better we design our suspensions the more extreme the crawling!
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Old 07-17-2001, 11:36 AM   #13 (permalink)
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Tin Bender, I know the pricipals i have stated you could find anywhere if you look. I am trying to remain in a Laymen's point of view so that everyone who reads can understand. If you want a more detailed response let me know. I understand that going to school and the real world are different. I am one of those people who believe you must build your ideas and see how well they work in the real world. Many people can spit out ideas and not have any sense of how to apply them. Should have went to Cal Poly so you actually had to build what you learned. By the way my name is not Brian!

Jimmy76FJ40, Just weld it and let it be! You don't have to worry about the airlines any more.

I am building a 63FJ40 sort of. When it is all done I don't know how much toyota will be left. But as the suspension progresses I will post pics. Does anyone need a set of high steer arms for a Dana44? I am thinking of making a few sets. Let me know!
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Old 07-17-2001, 11:37 AM   #14 (permalink)
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here's my problem.....
I work at the China Lake Naval Weapons Center, and I am surrounded by guys who have more deg. than you can count on both hands...
Yes, they are some VERY BOOK smart guys, but when it comes right down to it, they couldn't biuld a Snap-tight model...

True story: A guy with 6 engineering degrees asks me to the parking lot to show him how to change his wiper blades..NO SHIT!!!!
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Old 07-17-2001, 11:43 AM   #15 (permalink)
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Yeah, Looking back I wish I would have gone to CalPoly... I have a beach house in Morro and the "hands on "is the thing I missed most..
If you are infact putting the principals to work than I'll step back and say get it!!

Next time I'm in town, I'll buy the <IMG SRC="smilies/beer.gif" border="0"> and we can "talk shop" <IMG SRC="smilies/biggrin.gif" border="0">
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Old 07-17-2001, 11:47 AM   #16 (permalink)
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How does this sound, and what are the problems, and what would be better...

Rear mounts on the axle like front Ford C bushings - one per side. 2 links (one per side) from the C bushings in towards the center of the vehicle to a trailer stub axle pivot on a crossmember directly under the rear output yoke of the Tcase. The stub axle allows full 360 degree rotation, and a spring eye type poly bushing there allows for pivoting off of that s well. Both links will be attacked together at this pivot - basically a "V" with the point at the Tcase and the legs at the axle.
Springs will be handled by stock leaves, but with a shackle at both ends.
You are looking at a link length of roughly 38".

1. Will this work, or will the single pair of links (V link) cause the rear of the vehicle to raise up when you take off?
2. Will a panhard bar be necessary to control side-to-side movement of the axle when on the road/trail?
3. If this will not work, could the lower links ditch the C bushing type design for a spring eye poly mount and add a set of long upper links parallel with the leaf springs and control axle side-to-side movement as well as eliminate the rear of the vehicle wanting to raise up (is that what you mean by "anti squat"?)

[ 07-17-2001: Message edited by: DR. Mud ]
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Old 07-17-2001, 11:49 AM   #17 (permalink)
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This thread has to be a joke right? Come on stud you can't be serious about yourself can you?
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Old 07-17-2001, 11:57 AM   #18 (permalink)
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randii, you are correct
So where's my cookie? <IMG SRC="smilies/biggrin.gif" border="0">

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Old 07-17-2001, 12:10 PM   #19 (permalink)
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Depends on where you’re wheeling. Rubicon anti squat doesn’t hurt so much. Moab it is your worst enemy.

Questions for the god.
What effect does the mounting point locations on the frame have on anti squat?
What effect does the mounting point locations on the axle have on anti squat?
And why?
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Old 07-17-2001, 12:15 PM   #20 (permalink)
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1. Will this work, or will the single pair of links (V link) cause the rear of the vehicle to raise up when you take off? Yes
2. Will a panhard bar be necessary to control side-to-side movement of the axle when on the road/trail? Yes

advice, dont go there.
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Old 07-17-2001, 12:22 PM   #21 (permalink)
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Best link related math tip I can offer...
A 3/4" hiem joint will thread into a 1/2" pipe female fitting.
Some used pipe and some hiems answers alot of clearence questions cheaply.
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Old 07-17-2001, 12:28 PM   #22 (permalink)
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Quote:
Originally posted by Air Bag:
<STRONG>advice, dont go there.</STRONG>
Wow - now do you intend to explain your answers or are you just claiming un-questionable expertise like stud man up there? <IMG SRC="smilies/wink.gif" border="0">
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Old 07-17-2001, 12:29 PM   #23 (permalink)
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I agree that a degree doesn't give you the ability to become a god. I will have my Mechanical Engineering degree this December. I took a vehicle dynamics class last year that helped me understand some more about my CJ, but it doesn't make up for real world experience. We get our hands on training by building a mini-baja car. Full suspension go cart. You are actually tested at a competition. This is where you either put up or shut up. Most schools just put up and are satisfied with mediorocricy(sp). We, on the other hand went out to do our best design ever. It showed when we won one event and took fourth in another. With two cars, we finished 6th and 13th out of about 120 schools. That is hands on training.

So don't go spouting off your mouth about you knowing everything about link suspensions. Even what you think will work in your head or on the computer won't even come close to working. More times than not, it will end up binding and breaking things. The guys on here can build some of the most awesome link suspensions I have ever seen. If you want to learn something, ask questions from these guys and trade ideas. Don't think that your knowledge is soooo much greater than everyone elses. So back the fawk up and let everyone share their opinions and ideas. <IMG SRC="smilies/flipoff.gif" border="0"> You're not always going to be right.

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Old 07-17-2001, 12:32 PM   #24 (permalink)
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Quote:
Originally posted by willymutt:
<STRONG> You're not always going to be right.</STRONG>
Of coruse he isn't - I am the official "Know-It-All" of this BBS and everyone knows it <IMG SRC="smilies/tongue.gif" border="0">
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Old 07-17-2001, 12:34 PM   #25 (permalink)
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Dayyyyyyyummmmmmmmm Erin....
Smack'n like a pro!!!!! <IMG SRC="smilies/biggrin.gif" border="0"> <IMG SRC="smilies/biggrin.gif" border="0"> <IMG SRC="smilies/biggrin.gif" border="0">

Rapid city!!!! NO shit?? Hows life in the Big City?? I was Born in Rapid..... Still have Family in Custer <IMG SRC="smilies/biggrin.gif" border="0">
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