O.K , i've read the posts here for at least a year , and i've found them very fruitful for understanding old and new stuff .
But , regarding the most interesting issue - suspension geometry i didn't find a pure technical thread , which a guy like me, can understand the all issue from A to Z ( or at least A to G ).
So , i decided to put some thoughts and pics to start a comprehensive thread on that issue , anyone that can light up more ,is blessed .

My two axioms of the best suspension system are :
1- Let all 4 wheels , have constant contact with the ground.
2- Let all 4 wheels , have the highest vertical load .

Now let's go to the pic's :

Ho , i have problems to post the pic's , any one can help , please they are files on my hard disk .

post them to a web server and link them, or email them to someone who can load them for you.

Not too sure how many engineers there are here that are interested, but I am in for the thread.

Most here have found that suspension geometry is based on more real-world tuning then theory. As you can image when you alter an attribute to your overall suspension and steering configuration to increase a desired characteristic – you usually do so at the expense of another characteristic. The key it to have the best balance of these characteristics for your specific application (type of wheeling).

It would be nice to have a comprehensive listing of basic suspension and steering characteristics and the effects of various modifications. The information is “here”, just not comprehensive…

My current evaluation is of ‘buggy springs’.

Steve
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d<font color=red>/________\</font>b
<font color=black>|</font><font color=red>[</font><font color=yellow>O</font>=====<font color=yellow>O</font><font color=red>]</font>
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<font color=darkgray>[::]</font>-<font color=red>O</font>---<font color=darkgray>[::]</font>

right now i have buggy springs.

but i need longer shocks to make them work. i need longer shocks on the front too. i have a picture of them on my web page ( see signature link). if i had longer shocks it would flex like mad. i had the rear shocks off and it was cool. if i take off the front ones my driveshaft falls apart. still needs a little work but as soon as i can afford the shocks it will be sweet. here are some pictures! http://members.aol.com/beasttoyota4x4/images/buggyleaf2.jpg

http://members.aol.com/beasttoyota4x4/myhomepage/beastytoy4.jpg?mtbrand=AOL_US

:flipoff2:

Okay, I'll step out on a limb...

I really have not seen a control arm setup that i like. Coil-overs, coils 1/4 elliptic, and airbags are all superior methods of suspending weight, when compared to leaf springs. All of these offer more options, easy tunability, and extreme travel.
BUT - obviously, all of these methods require control arms. Now, with all of the common designs, 5 link, 4 link, 3 link - the more travel you try to get, the less control you have over the axle's movements.

Example- triangulated 4-link. If you make the arms short, and angle the uppers in very steeply, you get excellent lateral contol, but more axle-steer, you also get small flex. If you make the arms longer, they can travel farther, but the axle is freer to move sideways. Longer arms also help the vehicle's tendency to "jack" when torque is applied quickly. But trying to design link-type suspesions that are balanced front and rear is difficult because of the logistics. Drivetrain, shocks, axle locations are different front and rear, so it is hard to set them up the same.

People are always designing suspensions that travel farther, but is it really that important????

I would argue that it is more important to have a suspension that is balanced front to rear. If your truck has 60" of wheel travel, it should be 15" per wheel, not 20" per rear wheel, and 10" per front wheel.

Now - to leaf springs -
I believe leafs are the way to go, because it is easy to get a lot of wheel travel out of them, with out sacrificing axle control. I think thay are also relatively easy to tune. Most jeeps, LC's, etc. have narrower spring perches in the front, than in the rear. This means that the springs should be proportionally stiffer in the front. Too many lift kits for YJ's flex very well in the front, so-so in the rear. By adding spring rate to the front, you can actually get better traction because some of the weight will now transfer to the rear tires. If the spring perches are even widths apart front and rear, then use the same springs front and rear.

From what i have noticed, weight distribution does not tend to affect flex as much as i first thought it would. Someone confirm or deny this, because i haven't heard any other opinions on this matter.

So the keyword is "Balance" not "travel"

I think if you have around 5 feet of wheel travel, and you lift a tire on an obstacle, you need to be taking a better line.

did you check out the suspension god thread?

you can check out the god of suspension thread (you'll learn alot), just don't wake it up

What about DOUBLE triangulated 4-link:D

Originally posted by desertoy
What about DOUBLE triangulated 4-link:D

Holy shit! Thats what Im doin! Hows it workin for ya?

Works pretty good. Has absolutly NO rear steer too.

Originally posted by desertoy
Works pretty good. Has absolutly NO rear steer too.

SWEET! Thats what I thought!

Originally posted by desertoy
Works pretty good. Has absolutly NO rear steer too.

Do you have more info on this dual A arm set up?

Web page?

How the axle wrap?

Originally posted by desertoy
What about DOUBLE triangulated 4-link:D

Do you think that it would be streetable? I'm build a link type rear with coilovers but want to drive it on road occationally. and are all your links the same length

guy's , please help me with the pic - i'll show you a skatch that i've made - and we will carry on from that - it will help me to understand more .

Thank's

o.k let's see if it works
http://www.jeeptrip.com/upload/3cbe8ec5.jpg

I'ts working - let's roll :

Questions:
* what is the difference between intersection no' 1 , 2 , 3 ?
* what is the difference between intersection no' 4 , 5 , 6 ?
I think.. because of the job that these links ( upper links ) should do - lateral forces prevention - the angle a and b should be as wide as possible and there for the best intersection location should be number 1 and number 4 .

* What is the best length of the L letter ?
I think , that due to the fact of the need for that links , there is no importance for the length in the letral forces prevention subject , BUT , there is a imortance for the length if we will talk about axle movement - the shortest the L length would be , the more ravel the axle will have , because , these links provide axle movement up and down and also twist movement corresponded with lower links .

* Is there any importance for the locatiopn of the X points ?
I don't know .

After we will finish this issue i'll post a new sketch - side view .

Please feel free to reply , i want to learn more

Ido

what are the lower links? parrallel? angled?
if they are angled a ton they form 1/2 your roll axis, if they are close to parrallel they dont.
the suspension god thread had some great hints/suggestions/ideas as to where the roll centre should be in a 4x4. race cars try and shove low, i think the thread had it working out quite high(towards vertical CG) but the penis size contest began to make the thread unreadable so I gave up on it.
would be nice if someone knowledgeable would go through and edit the BS out and leave the arguments.

all the math you need to figure out the links is HERE (http://community.webshots.com/album/13190727rhRhHDXluW)
if that doesnt work go to 'chev power manual' HERE (http://community.webshots.com/user/ausername11)

the math is useless until you have an idea what you want the result to be for your application so throw out any mention in that book as it is circle track related

If i get this drawing correctly, the longer L is, the less lateral movement the axle will have, but also less potentail for travel, because the links will be shorter and more angled.

The X points are important for balancing the front and rear. I suppose it would be good to have those points exactly halfway between the centerline of each axle.

Like mj said, the lower links are also important in how the suspension performs. Desert Toy's design does seem to prevent axle steer, but it has not eliminated the lateral movement of the axle, and it is not balanced with the front suspension.
I'm sure you are planning on a coil-over front, or something DesertToy, I'm not picking on you. I know these things are never finished, but I am speaking in terms of an ideal setup...

Laters-

i disagree about the lateral movement thing, bushing and link deflection will determine lateral movement with any reasonable opposed angle on the links. i think it becomes harder on the links with less angle. could be way off on that never did any math....

Originally posted by elf_cruiser
If i get this drawing correctly, the longer L is, the less lateral movement the axle will have, but also less potentail for travel, because the links will be shorter and more angled.

The X points are important for balancing the front and rear. I suppose it would be good to have those points exactly halfway between the centerline of each axle.

Like mj said, the lower links are also important in how the suspension performs. Desert Toy's design does seem to prevent axle steer, but it has not eliminated the lateral movement of the axle, and it is not balanced with the front suspension.
I'm sure you are planning on a coil-over front, or something DesertToy, I'm not picking on you. I know these things are never finished, but I am speaking in terms of an ideal setup...

Laters-

Actually, Desert Toy's 4 link will eliminate virtually all lateral movement of the axle. It looks like it has heims at both ends so there wont even be any lateral movement from play in the bushings. I would like to see a side view of it to see how much anti-squat it will have.

Originally posted by WideJ
you can check out the god of suspension thread (you'll learn alot), just don't wake it up

can anybody link me to the "god of suspension" tread?

the search function mentions that "god" is too short a word to search for it... and suspension pulls up like 80k messages.

thx in advance,
alfred

http://www.pirate4x4.com/forum/showthread.php?s=&threadid=7503
searched by the usename 'calpolystud'

I don't know if anybody else here has thought of this, but: what would happen if you ditch the multi-links for locating the axle, and instead, used a single leaf on each side to locate the axle? And then still use coils to spring it...:idea:

Just a thought:D
Brandon

saw that exact setup on a jeep. the guy had one leaf on each corner, with coilover shocks had the springs under axle, the rig was very well balanced .

Originally posted by Im4yotas
I don't know if anybody else here has thought of this, but: what would happen if you ditch the multi-links for locating the axle, and instead, used a single leaf on each side to locate the axle? And then still use coils to spring it...:idea:

Just a thought:D
Brandon

It wouldn't work. By the time you found a single leaf that was thin enough to allow the coils to work through their full range of motion, they would be to weak to locate the axle.

O.k - the side view :

http://www.jeeptrip.com/upload/f5f57f20.jpg

I've sketched a side view of a common system - 4 or 3 link or any system that has two lower links and two upper links .

Questions :
* Where the hell is the roll center ? not roll axis !

*What is the best length for X and Y ?
I think that the shorter the length , the longer the axle movement BUT , is there any importance of the length for the all sysytem behavior ?

* Quote from ' Chassis Engineering ' - regarding ANTI SQUAT
" because any force that can raise the rear of the car will need
to have an equal and opposite force pushing against the
pavement , YOU CAN USE ANTI SQUAT TO INCREASE THE TIRE LOADING without adding to the weight "
now - i have understood from the GOD thread the the lower the anti squat the better !! SO who is right and who is wrong ?
I have sketched a system with more anti squat - should the links would be less angled ?
How can i measure the anti squat , if the links ( upper and lower) are parallel - they don't meet ?!

*What happens to the rear & front axles while accelersting ? - if the rear axle tend to roll backward , it pulls the chassis to him - lower - meaning more vertical load , if it rolls forward it will push the chassis higher - less vertical load ?! same for the front axle ?

* What is the best length between lower and upper intersection and the center of gravity ? who is more importent ?

More qeustions ahead .
Ido

first
in that new drawing where the front and rear lines intersect with each other is not relevant as far as I know

roll centre in that suspension is determined by the intersection you called #1 in your first drawing if the lower bars are parrallel or close to it.
info I have read on this site has the shown intersection much too low for 4x4 application(couple feet below the CG)

it is a road race book but it gives good definitions in laymans terms
http://community.webshots.com/album/19011079ZGcsLzpadE

o.k after hours of thinking , i think i'm starting to understand the issue above , and please post your minds .

First of all , 3 MAJOR SITUATIONS ACCURING WHILE DRIVING AND 2 ARE CRUCIAL FOR JEEPS :
1- QUICK ACCELERATION WHILE ASCENDING .
2- ROLLING FROM SIDE TO SIDE WHILE DRIVING OVER ROCKS OR
CORNERING IN FAST DRIVE.
3- STOPING .

regarding the first one listen carefully , I'd like it to be very basic and understood easily : while accelerating the chassis tend to squat at the rear - this action accrue cause the tires - axles - getting the torque - movement - sooner then the body above and there for , there is inertial force ( i hope i wrote it right ) .
Example - when a person stands on a bus platform and the driver starts driving , his legs starting to follow the floor movement while the upper body tends to stay where it was - in the real world it called inertia
NOW - the rear axle is getting torque and the 'corona' - the big gear start to roll forward , but there is a reaction from the axle housing that rolls the housing backwards - AXLE WRAP .
I didn't understood entirely this reaction - why , from and how much , because the inner axle mechanism is floating inside the housing and the bearings are absorbing the torque , i'll be thankful if somebody will post an answer to this .
Anyway - this movement of the housing backward perform a dramatic action on the chassis - THE LOWER SIDE OF THE AXLE TUBE GETTING CLOSER TO THE CHASSIS WHILE THE UPPER SIDE IS GETTING FAR FROM IT .
what it means - please look on my side sketch - the lower links tend to push the chassis up and the lower links pull it down .
Lets focus on the lower links - while the chassis squat downward the lower links push the chassis upwards - that means that if we locate the lower links in deferent places we can control the amount of squat - ANTI SQUAT .
If we locate the lower links very close to the rear of the chassis we'll get more ANTI SQUAT , the pure torque of the axle will overcome the squat of the chassis and if we'll locate it far at the front side of the cahssis the squat of the chassis will overcome the pure torque of the axle .
Graphic ? - look at the side sketch - at the rear wheel - there is a triangle form the lower mounts of the lower links at the axle to the upper mounts of the lower links on the chassis to the normal line ( vertical load ) that goes from the wheel to the chassis - THE WIDER THE TRIANGLE THE MORE SQUAT because squat has more place to generate and there for there is more vertical load on the wheels - more traction .
This vertical load is crucial to us , imagine the vehicle at 50 deg ascending , the driver pushes the paddle down, the chassis squats and the axle pushes it up , the line of the overcoming power from the axle will 'pull' the vehicle from the ground and will not let the forces focus to the wheel , we will spend more power to getting down than going up .

Now the upper link pulls the chassis backwards and there for putting opposite power to lower links .
In fact the upper links ARE HELPING THE CHASSIS TO SQUAT
( thats true only in 3,4 link setup not penhard setup ) .
The mounting point of the upper links at the axle are determining the amount of squat and the behavior of the sespension , if the mounts will be at the same height as the upper mounts of the lower links there will be a parrallel line ( to the ground ) and there will be no ' deformation ' to the power - the power will flow smoothly ( no rear steer and no under steer ) .
So , the more Squat you got the more traction you have and there will be more focus on power to the ground - vertical load .

I'll stop here cause , i want to listen what you have to say , please feel free to speak and correct me , if needed .


Ido

So is there a question here or...................Ok it seems like you are trying to say that more anti squat is good. If this is so, I disagree. Also, if the side view picture is ride height there are gonna be some problems. Your anti squat value is too high. Turn a corner and hit the gas and it WILL roll.

pig pen, what % antisquat do you think is a good # to shoot for?
race car books give general starting points for their application and there is nothing for 4x4.

i have read that the problem with high anti squat is that it can cause hopping when hit with shock loads. pounds suspension down for initial high traction then unloads.

there are tons of guys on here building good rigs.
all i want is a few generalizations of what to shoot for when i go links. the calpolystud thread gave me a hint on roll centre hieght, but degraded before the discussion was complete IMO

Originally posted by mj
pig pen, what % antisquat do you think is a good # to shoot for?
race car books give general starting points for their application and there is nothing for 4x4.

i have read that the problem with high anti squat is that it can cause hopping when hit with shock loads. pounds suspension down for initial high traction then unloads.

there are tons of guys on here building good rigs.
all i want is a few generalizations of what to shoot for when i go links. the calpolystud thread gave me a hint on roll centre hieght, but degraded before the discussion was complete IMO

I'm trying to remember/reconcile what I've read in Race Car Dynamics (SAE Press, Milliken and Milliken) and a couple of Carroll Smith's books (Engineer to Win, Tune to Win)...

If memory serves RCD states a range like 20-30% anti-squat in the rear and anti-lift in the front is a good starting point with the specific number being tuned for conditions and/or driver preference.

I think it stated most road vehicles (non-sporting) are in the 10-12% range. Smith made the point that too much anti-squat or lift will be murder on the suspension pickups - this is where the forces are reacted. Also, there is the point that you made about the suspension tending to jumping around under load and hard surfaces.

I think a reasonable place to start would be around 10-15%, especially if your suspension has a way to adjust it after the fact. I'd prefer to have to little than too much and some of the lift/squat can be reacted against with a stiffer setting on the ranchos to some extent.

But then, I tend to think in terms of on-road performance first.

If you want, I can get the specific quotes on the topic from these references - if it would be helpful.

I am gonna have to dig out the Millikin book to read up if you want #'s. Getting the links as parallel to the ground as possible is a good starting point.

Originally posted by mj
pig pen, what % antisquat do you think is a good # to shoot for?
race car books give general starting points for their application and there is nothing for 4x4.

i have read that the problem with high anti squat is that it can cause hopping when hit with shock loads. pounds suspension down for initial high traction then unloads.

there are tons of guys on here building good rigs.
all i want is a few generalizations of what to shoot for when i go links. the calpolystud thread gave me a hint on roll centre hieght, but degraded before the discussion was complete IMO

Originally posted by Pig Penn
I am gonna have to dig out the Millikin book to read up if you want #'s. Getting the links as parallel to the ground as possible is a good starting point.



Yep, and as long as is practical. the longer the links the less the effects of geometry change on the caster/pinion angle at the axle end.

Two parallel links per side of the axle might be good compromise for keeping angles the same if the packaging works but then you have to look at what it does to the roll axis for each axle.

Solid axle suspension design is a real compromise, I think you get the best of the compromises if you use long links and then try to get the suspension as stable as possible. The long links can't help but let it articulate well.

first of all , nobody has answered my post - is it true or wrong ?
Second , if there is no compromise at all , what will be the best sespension setup ?
Third , why do you think that less anti-squat isn't better ? meaning - the more the squat the more vertical load on the tires or more directed forces to the ground , or , do you think there is a better way to achive this ?

Originally posted by ido
first of all , nobody has answered my post - is it true or wrong ?
Second , if there is no compromise at all , what will be the best sespension setup ?
Third , why do you think that less anti-squat isn't better ? meaning - the more the squat the more vertical load on the tires or more directed forces to the ground , or , do you think there is a better way to achive this ?

Is what true or wrong? Please state your question in one sentance. Compromise is a key word here. Less anti-squat is better IMO. As for a better way to achieve more directed forces to the ground...........maybe some hydrolics???????? Low Rider style...

Big penn , my question in two sentances is :
* Is it true ? QUOTE]Anyway - this movement of the housing backward perform a dramatic action on the chassis - THE LOWER SIDE OF THE AXLE TUBE GETTING CLOSER TO THE CHASSIS WHILE THE UPPER SIDE IS GETTING FAR FROM IT . [/QUOTE]

* Is it true that a line from the lower mounts , of the upper links to the upper mounts of the lower links , is the roll axis ?[The mounting point of the upper links at the axle are determining the amount of squat and the behavior of the sespension , if the mounts will be at the same height as the upper mounts of the lower links there will be a parrallel line ( to the ground ) and there will be no ' deformation ' to the power - the power will flow smoothly ( no rear steer and no under steer ) .


Thanks in advance

desert toy, i notice in your first pic yah have shocks and i dont see them in the action shot. what gives? do you remove them when wheeling or did you move them and im just not seeing them?

I don’t think that you want to use any intersection points between front and rear suspension components. X in the first picture and length X and Y in the second sketch are irrelevant points. There are some values that you want to balance front and rear but they are values derived from the complete geometry for that end of the vehicle not values derived from front and rear components. Some of the values that you want to balance front to rear are roll center height, roll rate, and ride frequency.
The angle of the upper links and the compliance of bushings vs. rod ends do play a part in lateral stability. But to “ Engineer “ the links is a bit more complicated, you need to at least understand the basics of engineering “static’s” and “strength of materials”, these classes are sometimes available at junior colleges but you need a good handle on trig to take them. If you don’t want to go this route than keep the angle between them large and make them strong.

P.S. don’t over triangulate the lower links but do triangulate a little bit.

But to “ Engineer “ the links is a bit more complicated, you need to at least understand the basics of engineering “static’s” and “strength of materials”, these classes are sometimes available at junior colleges but you need a good handle on trig to take them
I do understand the besic engineering cause it took me couple of years to get my diploma in mechnical engineering , but , let's say that after chosing the right links ( tubes ) for the mission , what will be the best geometry to locate them ?


P.S. don’t over triangulate the lower links but do triangulate a little bit. - why ?
My plan is a big A arm as the lower links and the intersection of the two , will take place under the transfer case as a one big pivot which allow the axle articulate very easy .

Does , two triangulate links ( lower and upper ) is the best way to fight rear steer and to get a parallel roll axis ?


Thanks in advance

You could be weird like me and use a 3 link on each axle with panhards. There are tradeoffs with every kind of suspension design. The things you have to consider usually end up being dictated by what fits your vehicle or if you are starting from scratch.

I made a 3-link with panhard up front with 1 lower link on axle centerline and 2 longer ones on top. The lower single link is also offset to the differential side and by doing some "compass math" on graph paper and some simple trig I figured out where to place the endpoints on the frame.

Not sure how it will work on the trail, but I figured I'd try something different!

Squash
p.s. I don't know where you got the center of gravity on those drawings, but I suggest you ditch it before confusion permanently sets in.

Ido if you have an engineering degree then it should be simple for you to understand anti squat. get out your dynamics book if you need a little review on instant centers. you can find the side view instant center by simply looking at the side view in two dimensions and drawing lines through the mounting points of the upper and lower links. Where these lines intersect is the instant center. You seem to want them to be parallel which is not the best idea, but if you do that the instant center is located an infinite distance out along one of those lines. the instant center is the point that the forces must be reacted through, so when you draw the force vector at the contact patch it must be at an angle that will go through the instant center. where this force goes in relation to the CG will control what happens to the vehicle under acceleration. For example if it passes directly through the CG there will be no moments on the sprung mass and it will not squat at all. This is refered to as 100% anti squat in most of the racecar books. You were on the right track looking at how the lower links push up on the chasis and the upper links pull down. If you sum the forces and moments on the upper and lower links you will come out with the same reaction on th sprung mass as with the insant center method but it is a lot moremath.

As to what you want that is hard to say, but I can tell you what you don't want. You don't want the anti squat to be so high that the suspension lifts to the point that it tries to walk under its self. this means that at full droop the anti squat should be less than 175% or so. Unfortunately with a 4 link/3 link/ radius arms as the suspension travels down the anti squat increases. With a leaf spring suspension the opposite is true.