CK5 - The Full-Size GM Off Road Community

I've been absorbing myself in theory lately over different technical considerations as applied to suspension. While I'm looking to make some exotic changes to my own vehicle and gather knowledge pertaining to that change, I'm finding quite a bit of information that is pertanent to calibrating stock suspention, slightly modified (like lift kits) and right on up into complete custom designs. There is quite a bit of information available on calibrating and/or designing suspension targeted toward street, baja or rock climbing but very little on creating a well rounded vehicle which has adequite capabilites in all of the above at the expense of being exceptionally good at any one of them (hmm, sounds like a production sport utility, eh). If everyone is to get something out of this, I think a quick glossary of terms is in order and then we can play around with how they combine to excel in different areas. I want to clarify from the get go that I'm a complete novice and have never formally applied these elements on a full size vehicle so those of you who have, pipe up and add in the real world experience. So, from what I can gather:

Spring -
-A spring is an elastic device that resists movement in its direction of work. The force it exerts is proportional to the movement of one of its ends. Or to put this into a mathematical equation: Force = movement * spring constant. A high value for the spring constant makes for a stiff spring, and a low value makes for a soft spring. For progressive springs the spring constant will increase as the spring goes deeper into its travel, and for regressive springs it will decrease with travel. So math wise, springs aren't very complicated, but handling wise, they are. This is because the springs have to absorb the torques that are generated The problem is that they work in two dimensions: left to right and front to rear. Springs inhibit weight transfer, both front-to-rear and left-to-right: for the same cornering, acceleration or braking force a stiffer spring will compress less, resulting in less chassis movement and thus also less weight transfer, and a soft spring will compress a lot, resulting in a lot of weight transfer. Springs store and release energy.

Unsprung / Sprung Weight-
-Sprung weight is the weight supported by the springs. For example, the vehicle's body, frame, motor, and transmission would be sprung weight. Unsprung weight is the weight that is not carried by the springs, such as the tires, wheels and brake assemblies.

Dampening (shocks)-
- Damping is needed to absorb the energy associated with suspension travel and results in the generation of heat. In terms of energy, damping absorbs most of the energy the truck receives as it moves, unlike springs, who store the energy, and release it again. Dampers absorb all the excess energy, and allow the tires to stay in contact with the ground as much as possible. This also indicates that the damping should always be matched to the spring ratio: never run a very stiff spring with very soft damping or a very soft spring with very stiff damping. Damping that's a bit on the heavy side will make the truck more stable; it will slow down both the vehicle's pitch and roll motions, making it feel less twitchy. Note that damping only alters the speed at which the rolling and pitching motions occur, it does not alter their extent. So if you want your vehicle to roll less, adjust the springs, but not the dampers.

Roll Center/ Instant Center -
- A roll center is an imaginary point in space, look at it as the virtual hinge your car hinges around when its chassis rolls in a corner. It's as if the suspension components force the chassis to pivot around this point in space. The roll center is also the only point in space where a force could be applied to the chassis that wouldn't make it roll. The roll center will move when the suspension is compressed or lifted, that's why it's actually an instantaneous roll center. The roll centers/instant centers transfer the non-rolling forces to the road surface. The height of the roll centers and the instant center placement determines how much of the weight transfer at either end (front and rear)goes through the springs/shocks (rolling) and how much goes through the geometry(non-rolling). with low roll centers the springs and shocks transfer the majority of the weight. With high roll centers the location of the instant centers and any panhard bar take care of teh majority of the weight transfer.

Center of Gravity -
- Center Of Gravity is the spot within a vehicle where there is equal weight all around it.

Roll Moment -
- The vertical distance between the Center of Gravity and the Roll Center

Anti Squat-
- Anti-squat describes the angle of the rear hinge-pins relative to the horizontal plane. Its purpose is to make the truck squat less when accelerating. (Squatting is when the rear of the truck drops down when the truck accelerates)
More anti-squat will give more 'driving traction': there will be more pressure on the rear tires as you accelerate, especially the first few meters. At the same time, it will give more on-power steering, because the truck isn't squatting much. The disadvantage is that the truck has an increased tendency to become unstable entering corners, especially in the rear. Reducing the anti-squat angle has the opposite effect: a lot less on power steering, and more rear traction when the truck isn't accelerating as much anymore. The truck will also be a lot more stable entering corners. It also affects the truck's ability to handle bumps: more anti-squat will cause the truck to bounce more when accelerating through bumps, but it will increase the truck's ability to absorb the bumps when coasting. Reducing the anti-squat does the opposite: it improves the truck's ability to soak up the bumps under power, but reduces it while coasting.

Ride Height -
- Proper ride height is very important, too low and the vehicle will bottom out a lot, too high and the risk of traction rolling will be unnecessarily big. Equal ride height front and rear is a good starting point. Raising or lowering ride height on one end of the truck changes the steering characteristics of the truck, the lowest end will have a slightly bigger percentage of the trucks static weight. But, more importantly, the roll center will also be lowered, making that particular end of the truck roll deeper when the truck corners, making it sit even lower and thus having more grip.

Suspension Travel-
- The amount of negative suspension travel (downtravel) a truck has can have a huge effect on its handling; it influences both the mount of roll and the amount of pitch the chassis will experience. An end with a lot of downtravel will be able to rise a lot, so chassis pitch will be more pronounced, which in turn will provide more weight transfer. For example: if the front end has a lot of downtravel, it will rise a lot during hard acceleration, transferring a lot of weight onto the rear axle. So the truck will have very little on-power steering, but a lot of rear traction. A lot of downtravel at both ends, combined with soft springs, can lead to excessive weight transfer: on-power understeer, and off-power oversteer. The cure is simple: either reduce downtravel, or use stiffer springs.

Sway Bars-
- Anti-roll bars are like 'sideways springs', they only work laterally. Here's how they work: if one side of the suspension is compressed, one end of the bar is lifted. The other end will also go up, pulling the other side of the suspension up also, basically giving more resistance to chassis roll. How far and how strongly the other side will be pulled up depends on the stiffness and the thickness of the bar used: a thin bar will flex a lot, so it won't pull the other side up very far, letting the chassis roll deeply into its suspension travel. Note that the bar only works when one side of the suspension is extended further than the other.

Weight Transfer -
- Newton's third law, force = mass * acceleration, implies that whenever the vehicle accelerates in any direction, additional forces occur. For example, when your car lands after having taken a jump, its downward velocity decreases rapidly. Basically, it stops falling down quite suddenly. The extra force associated with this equals the mass of the car times its acceleration.

Transverse Weight Transfer-
- Transverse weight transfer occurs because the driveshaft torque reacts between the frame mounted engine and the axle. The engine, which is a part of the sprung weight, produces the torque through the transmission. The rear axle has to resist that torque at the rear tire patch. Transverse weight adds cross weight under acceleration and removes cross weight durring deceleration. The manatude of teh transverse weight shift is a function of the instantanious engine torque and the roll stiffness.

Lateral Weight Transfer -
- Is the Weight Transfer from one side of the vehicle to the other.

Longitudinal Weight Transfer-
- Is the Weight Transfer from one end of the vehicle to the other.

This is a good start, any feedback or corrections before we start throwing all this together?

Sorry I really don't go into the mathematical influences of the suspension but I do have a lot of real world experience in watching different suspensions and how they work. For all intensive applications (Rockcrawling, Trailriding, Towing, Highway driving etc) the leaf spring situation seems to do the best. A Moderately soft leaf spring with long travel shock will flex more than any sane person needs. They will have very good manners on road, they are simple to design your suspension with and they are by far the lowest maintenance. For example my friend has a Jeep Grand Cherokee with 4 link coil springs front and rear from the factory and he added the most expensive lift you can buy for it which gives him 4.5 inches. His Grand is very flexy and rides fairly nice but my K5 just has a Rancho 4 inch lift with ORD shackle flip and it ramps just as high and I can trailer his rig to moab. Recently we went down for Jeep Safari and he crashed into a rock pretty hard smashing his lower control arm mount bad enough that he could not drive home, if he had leaf springs he would have finished the trail and drove home. You now probably think that I am not open minded about more custom suspensions. I love the way that a 3 link airbag or king coil over suspension flexes but I have seen the performance at rockcrawling championships and they are really limited by the same thing as leaf springs which is usually shock travel. Too much articulation is a bad thing no matter what you have heard. If you have a long travel shock I guarantee that with 1 locker that you will be as well off as the guy with 3 or 4 link and open diffs or 1 locker. Sorry I made it so long but I searched the same as you probably are and I looked really hard at airbags because they were somewhat cheap but I decided to just do what Steve Fox did. and here you can check it out.

http://coloradok5.com/ranchoreview.shtml

/forums/images/icons/smile.gif See You In Moab

I think you are spending too much time thinking about this stuff. I finally looked at your profile to see that you are an engineer, go figure. LOL. Just build the truck like everyone else and drive the damn thing. LOL

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Springs inhibit weight transfer, both front-to-rear and left-to-right: for the same cornering, acceleration or braking force a stiffer spring will compress less, resulting in less chassis movement and thus also less weight transfer, and a soft spring will compress a lot, resulting in a lot of weight transfer.


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This isn't quite right...
Spring rate does not have anything to do w/ front-to-rear weight transfer (well not much). The only diffenence they make is if the front dives more on breaking the CG will move forward (what maybe 1" max?) and that will cause a percentage of the weight from the rear of the truck to be transfered to the front. It is such a small amount that it is usually neglected. Weight transfer (front-to-rear) is considered to be a function of CG location and acceleration (like breaking).

Lateral weight transfer is affected more by the springs than side to side because both front springs will be the same rate and the rear will also match side to side (at least they should...LTO not encluded). If one end of the truck has a lower roll rate (dependant on the spring rate but not the same...it also depends on how far apart the springs are) less weight will transfer to on that end. That is if the front has a softer roll rate than the rear the rear will transfer more weight to the outside tire (and resulting in less rear traction) than the front does.

Shocks:
It should also be noted that the energy they absorb will be turned into heat.

Anti Squat:
I aguree with the def...but not with what the effects are...but don't have the time to explain (see above about weight transfer).

You make some really good points. One of the reasons I wanted to get this discussion going was to validate the different reasons for having the different suspension designs, get people familiar with what they have and the reasons the factory chose those options. I think the majority of people here drive their truck to the area they off road so highway manners are very important. I've been searching for that fine line of minimal road sacrafices with minimal off road sacrafices where adjustability and disconnects can help improve the advantages. I like the idea of exotic setups to combat axle wrap, alter stock antisquat characteristics and change travel/dampening based upon terrain.

I think I understand what your saying. Rather than springs inhibit weight transfer, it should read springs provide weight transfer. If the springs were removed and solid mounts were to take their place, there would be no axle travel and aside from the tire sidewalls, the body movement would stay flat and thus eliminate stored energy previously associated with the spring.

Good note on the shocks as heat can change a shocks characteristics.

I'd like your input on the anti-squat when you have time.

Argh, now I know why I changed majors from engineering. There's no way I can even read all of that without going nuts. Btw, my dream suspension on the rig would be 1/4 elliptical rear and modified leafs front. But I've been spending way too much time designing and way too little time driving, thus my toys are beginning to own me. Hate it.

I know what you mean, just getting familiar with all these terms is one thing but then turning around and applying them while trying to determine their effects on each other gets complicated. I like the buggy spring idea too.

I'm finding it realtively easy to determine an approximate instant center on link suspension and how running parallel links which are parallel to the frame have different anti-squat characteristics as parallel links which are angled to the frame. When you apply the same concepts to a 1/2 eliptical setup (stock leaf spring), changing mounting points such as a shackle flip should also change instant center but having a link which can bend makes it more difficult to calculate it. Kind of like a buggy spring would be ...

http://www.echobit.com/images/buggyleaf.gif

roll centre and instant centre are not the same thing.
off the top I cannot think of a suspension where they are the same point. was thinking Unimog torque tube but they have a panhard that I believe creates a roll axis

I like the 1/4 elip more n more
i like that you can add leaves under the pack to prevent droop and hopefully transfer some more wieght to the tractive tire.
that cant be done with coils or bags.
I still like the bags for their constant ride hieght regardless of vehicle loading. also some of the antics you can perform with incab controls like, lift any tire so no-jack tire changes are possible in some vehicles, or dumping the air to allow easier egress
other then that they act like coils.
new they are $$$ used I have bought them for $50cdn

Your right, roll center and instant center are different. I clumped them into the same description because they had similar traits. I tried to differntiate between the two in the description but perhaps I should reword it or sepperate them and inlcude a graphic.

I'm still looking into the air bags as an option. Its a neat solution.

What do you think about the shackle flip and potential squat characteristic change, it seams that axle wrap could change the instant center as well.. any thoughts?

I'm with MJ on this one. I like the 1/4 eliptics, but I want to combine them with air bags for adjustable ride height and higher rate springs (for when the bags are deflated, like fire roads or off camber). I'm dreaming again, I'll never get around to doing it, but I think that's the way I would go if I got the wild urge, lots of time, and "found" a bunch of $$$.

Anyway, still following this thread with a great deal of interest. I've seen allot of this stuff referenced but never quite understood allot of it. No reason to spend much time on it since I don't plan to pursue it. Also, some of the guys on POR have referenced a book that cover’s allot of these suspension calculations and considerations. Might do a search there.

BadDog - I've been through about 6 off road forums so far and found lots of information on this topic... but nothing here, so I'm starting it.

Traiged, I understand what you mean now to a further extent. Movement of the spring mass does not cause weight transfer but does change the center of gravity height.

"The only thing that causes weight transfer is lateral or longitudinal force acting on a center of gravity (CG) that is above the ground. All cars, no matter the suspension geometry or wheel rate (indeed, even with no suspension at all), have a CG above the ground and therefore must transfer weight when acceleration force is applied. The CG forms a lever between itself and the ground through which the acceleration forces acts, and the wheelbase forms the lever through which the force acts on the wheels. That means that the only way to reduce weight transfer is to lower the CG (shorten its lever arm), or increase wheelbase or track (to decrease the mechanical advantage the force has on the wheels), or to lighten the car overall (which reduces the force at its origin)."

Where springs inhibit weight transfer is in inhibiting the movement of that center of gravity height. So I should change the wording to springs inhibit the change in the center of gravity height and further define center of gravity. Sound better?

in my webshots album 'chev power manual' there is a section on the hotchkis suspension.
it shows a point C as the instant centre but I am having trouble determining what locates C.
the length is 3/8 of spring length but the angle is a mystery to me so far. will have to read it a few more times

I think this forum is more capable of a useful discussion then P4x4.
there are some extremely knowledgeable folk there but the XXXXXs drown out any intelligent ponderings.
all that is really needed is a list of rules of thumb and some generalities of what trends cause what effect at the limits.
something like "the rollcentre works well within X distance from the cg hieght, higher and Z is the result, lower and Y is the result"
for extreme anti squat I know that under braking you can have it nearly lift all the pressure from rear tires.
I would also like to see if the front straight axle math is a mirror of the rear.

www.community.webshots.com/storage/1/v1/0/16/43/13201643pDbEKiLxQy_ph (http://www.community.webshots.com/storage/1/v1/0/16/43/13201643pDbEKiLxQy_ph)

www.community.webshots.com/storage/1/v4/0/16/48/13201648cDNsWVGxwr_ph (http://www.community.webshots.com/storage/1/v4/0/16/48/13201648cDNsWVGxwr_ph)

Everyone should bookmark this (and MJ should put it in his sig).
http://community.webshots.com/user/ausername11

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More anti-squat will give more 'driving traction': there will be more pressure on the rear tires as you accelerate, especially the first few meters

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This is the part I don't really agree w/. Longitudinal weight transfer is caused by acceleration, distance of the CG above the ground, and wheelbase. The only other way to get more weight on the rear tires is for the body to be accelerating upward! That could only be kept up for a short period of time and could never (in any normal truck) be that great in manitude. Anti-Squat will also bind up the suspension under acceleration (what prevents the squat) which will cause the tires to hop and loose traction when they hit a bump (and arn't bumps what we are looking for when we go offroading?).

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At the same time, it will give more on-power steering, because the truck isn't squatting much

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How would the truck steer better w/ anti-squat because it does nothing about weight transfer? The weight on the front wheels will not change as a result of anti-squat (of course the caster angle will change as the rear end squats and the driver will see more hood and less road but that is beside the point).

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It also affects the truck's ability to handle bumps: more anti-squat will cause the truck to bounce more when accelerating through bumps

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This is 100% right
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but it will increase the truck's ability to absorb the bumps when coasting.

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This is a very small change and most drivers would not even notice it...wheel hop they will.

That buggy setup looks pretty "spiffy", LOL. I really like that idea. Would it require any locating links to keep proper geometry? I have never really paid attention to buggy designs, mostly flexy leaf and multi-link w/ coils. But, I think a retaining bracket could be devised where the buggy rests on the frame to fix it in place for DDing or when not needed. I don't know from personal experience how a buggy would react on the road, but I could almost guarentee that fixing it to the frame, effectively removing all of it's Pros, would remove all of the Cons of using it on the road. Does anyone have any more info on this type of setup? TIA!
Later...Allan

"More anti-squat will give more 'driving traction': there will be more pressure on the rear tires as you accelerate, especially the first few meters"

Is your disagreement on the nature of antisquat surface related? On a vehicle with lots of antisquat, lets say a drag car on smooth level asphalt, the vehicle will rise under accelleration moving the chassis upwards which essentially forces the tires down(directly proportional to torque and weight). This results in traction. A truck on level asphalt should exhibit the same characteristic and does. Where the bouncing comes from is the stored energy in the suspension getting triggered by an imbalance. On large trucks its usually a characteristic of soft suspension without an antisway bar on the rear. For a rock crawler, this is kind of mandatory and hence the different reaction. But this doesnt change the fact that it also affects the truck's ability to handle bumps: more anti-squat will cause the truck to bounce more when accelerating through bumps because of the torque applied to the wheels, which is trying to extend the suspension downward (remember, forcing the vehicle up) and adding resistance to its full range of motion. I think, and could be mistaken, that your jumping ahead to the application of antisquat as opposed to the concept of it which I simply want to define for later discussions.

As far as anti-squat binding up the suspension, I agree that excessive antisquat would do just that, just as excessive squat would do the same.
Great point of discussion though, the application of antisquat is totally different depending on what your using it for.

The on power steering is something more relational to the position of the front geometry as opposed to weight transfer. With more antisquat, the front tends to extend less into its full range of motion as teh vehicle rises. With a lot of squat, your more likely to have the front suspension extend further(as the back drops) and put the suspension geomety in a less desireable state. This is where the increase in stearing comes from, alignment. This is especially important on independent front ends.

I agree that most people will not notice the increased bump absorbsion durring squat but it follows the same properties of torque applied to the range of suspension motion.

I apreciate your involvement in this thread, it helps the discovery process and makes for some good info exchange. How does the above sound? Think were ready to start applying it to our rigs... its where the most debate starts.

I think a panhard bar is required to keep from excessive axle walk (side to side) on the buggy springs. I almost did this to my truck but talked myself out of it... looking back though, I've got everything I need to try it out now. Hmmmm. don't think I'd keep it though.

you are definitely going to have to explain where antisquat will bind the suspension.
it is simply the pushing and pulling on the links being used for something.
everytime this comes up people take it to extremes.
100+% antisquat would cause a bunch of things that I wouldnt like but having some seems to be a necessity.
how much is what I dont know.

You get too technical and you'll just be another guy with a torn down truck in the garage for ten years that you end up taking a loss on to buy a new house. Do something simple 4 wheel it tow with it drive it and fix broken parts. You may make something cool but you'll be too old to enjoy it. Other than that you guys are making this High School Senior's head spin. I appreciate the input but really this is just like math class. In two years when you are done designing your suspension we'll go to moab and the extra experience I have gained in driving on the trail will get me farther than the most trick suspension that I've ever seen. If you want to see something cool just look at the ORD Jimmy nuff said. I'm not making fun of anyone just acknowledging that you are definitely smarter than I am.

Good Luck

/forums/images/icons/smile.gif See You In Moab

I wouldn't say anyone is smarter than anyone here. If we were all talking about the length of an inch we might get into a guage of smarts but with all the factors here there are too many ways to be right! I agree that you could easily down a truck for a good 10 years doing stuff like this but I'm building my suspension in the garage and wheelin the truck every day. When I'm happy with the suspension, I'll bolt it up and give it a shot. If it doesn't work, I'm going to unbolt it and return it to what it is now, go wheeling and think of something new. My truck is a daily driver, and I intend on keeping it that way. Weekends are my only possible down time so whatever I do has to get done and be functional that fast. I've got my 14bFF w/Disk sitting here easy to work on so I'm taking this opportunity to weld on linkages, truss, shave the bottom all the other fun stuff while its easy to get at. Should be fun.

I'm glad you aren't getting too serious here but if you are able to do your suspension just that easy you will have to let us all know how it turns out and if it is good then you might need to share some of the secrets that you find.

I think the best secrets shared with me by a bunch of others on a bunch of other boards who have done exotic setups could easily be shared now:

1. If you can make it bolt on, do so. Especially if it doesn't interfere with returning it to its previous condition.
2. Make everything adjustable. Every link, every mount... everything.
3. Be conscious of your Center of Gravity(keep it low), Roll Center, Sprung-Unsprung weight, Instant Center and a balanced squat / antisquat.
4. Be prepared to have less than desireable results the first time.

Many people but the advise was all the same.

Quoting Carroll Smith:
"Once more we are resisting the natural downward force of load transfer with a reactive uppward thrust so it is possible to lose sensitivity and get into tire patter and the like if too much anti squat is emploied. This will manifest itself as power on oversteer." He says it much better than I ever could...maybe bind isn't the right word.

If you are looking for some #'s to start w/ he says 30% max anti-dive (on heavy front engined cars...I guess we are included in that someware) and for anti-squat. "About 20% seams to be the maximum before we get into tire compliance problems. The lower the power to weight ratio, the less is required -or can be tolerated."

1 in. = 25.4mm We have been on a metric system for a while and haven't known it. /forums/images/icons/tongue.gif

what year was he writing that?
my stock mustang has 39% anti squat and I am adding more.
my book states nearing 50% you will start seeing negatives for road racing.
niether number is necessarily relavent to a tall 4x4

that attitude is why there is so much junk out there.
it takes the same time to weld a bracket in the right place as the wrong, and they both look fine to the eye.
so if all it takes is a few measurements to make a more stable rig I say lets work at it.

Oh boy... I knew someone would do that! LOL
next we'll be swapping pressure conversions of an inch like
1 inch H2O (60 F) = 2.537532 cm H2O (4 C)

hahah

This is about the only thing I have to contribute. (for those, picture book kinda guys, like myself. /forums/images/icons/smile.gif)
<a target="_blank" href=http://community.webshots.com/photo/36269607/36269714iGRfBl>http://community.webshots.com/photo/36269607/36269714iGRfBl</a> &lt; crappy drawing, but the point is how the front spring eye height effects anti-squat w/leaf springs.

Cool topic, Good post. I've been wating for something like this break-out.

Dig your sig too,/forums/images/icons/smile.gif

that is kinda how I assumed it worked as well Twisty, but the manual puts the IC at 3/8 the total spring length from the axle at an angle that I still havent figured out how they came up with, as opposed to the easy front spring eye.
the drawing is still bang on just the IC point is closer to axle

It looks like the angle that it is inclined at is based on that 3/8 L equivalent link which goes from Q to R (R being on the main leaf).

Maybe I should go out and measure how much anti-squat i gained by adding the shackle flip and how much I will loose when I go to 63" leaves...I'm getting currious as the suspension design I have done and tuned have had no anti-squat/dive at all (and I don't plan on putting any in)...but that is for a 450# autocross car which is a hole different story. I'm still trying to sort all this big heavy truck stuff out for myself so bear with me.

I'm very interested in the instant center characteristics of a leaf spring. Since the spring exhibits axle wrap under torque load and deforms, perhaps thats the confusion on the location of instant center? Something different on the Hotchkiss design which I've been finding a small amount of reference to is the difference in mounting the axle over or under the leaf pack to antisquat.

Additionally, I'm finding a lot of information related to spring rate and the shackle angle:

http://www.echobit.com/images/LEAF_3.gif
http://www.echobit.com/images/LEAF_4.gif

I like that explaination.

so are you saying you have the force vector intersection at the ground below the cg?
both upper and lower control arms aim down to this point?
seems you would be giving up bite out of the corners.
front and rear or just rear?

http://community.webshots.com/storage/1/v5/1/28/10/36312810uqMxjq_ph

The green dot is the roll center.
Other specs:
No king pin inclination
~2" scrub radius
~8* caster

-.84* camber in 1" bump
.001" track width change in 1" bump
Roll center moves to -.39" in 1" bump

I was looking to get the roll center close to the ground, minamize track width change, minimize camber change in bump and droop, maximize camber compensation in roll.

The anti-squat will not be easy to adjust in the rear because of the double A-arm suspension so most likely it will be left at 0%

This is a pic of our 2000 car (we won 3rd out of about 120 schools and 1st out of about 50 schools at the compitions we attended).
http://community.webshots.com/storage/1/v4/1/41/14/36314114GJfbEh_ph
Right now there is 2 of us (including me) designing the suspension, chassie, and steering for the 2003 car.

I just don't get that shackle angle vs. rate as shown.

Assuming a positive arched spring like we have in the rear (or with lift in the front). With the upper eye ahead of the rear spring eye (arc "A") the rate should be softer. As the axle and frame move closer together, the rear spring eye moves toward the frame (unload) AND the spring is forced to deform only by flattening a little. However, on the "B" arc, you have the "load" affect for positive arched springs. In order for the axle to move toward the frame, the spring MUST flatten out, which forces the rear eye toward the back, which, in turn, forces the eye DOWN away from the frame. Hence, a “load” affect. This is fighting the effort to move the axle toward the frame by forcing the spring to flatten out quite a bit more. If you break down the force vectors at the shackle, you can also see that everything is working against you here.

In short, I believe those pics are only true for flat springs and negative arched springs. Am I missing something?

I never thought about spring wrap...
Good point because that would have ALOT to do w/ anti-squat. You would have variable rate anti-squat (loosing anti-squat right?) depending on how much spring wrap you have. Seems counter productive!

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The anti-squat will not be easy to adjust in the rear because of the double A-arm suspension so most likely it will be left at 0%

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isnt that a matter of simply(doesnt that make light of hours of work) adjusting the control arm mounts vertically.
good image of pickup points on front suspension. is that something similar to Performance trends or your own drawings?
anything on side view?

BadDog, your thoughts are exactly in tune with my initial reaction. The second image link shows the loading and unloading characteristic of the shackle position and its motion arc. The arc is what is important here. From 90* to 0*, the horizontal distance that the shackle travels starts fast and gradually slows until at 0* it stops travelling all together. The same is true from 90* to 180*. In a positive arch spring durring compression with a forward mounted shackle, the spring length is increased horizontally but the shackle arc is resisting this due to its speed decreasing on the way to 0* (it was already past 90* to begin with). If the shackle was mounted back, its speed would increase as it rounded the 90* point then decrease on its way to 0*.

Great Question by the way!

"matter of simply(doesnt that make light of hours of work) adjusting the control arm mounts"

Yes that is ALL it takes. But when you have few chassis tubes (we might have 4 past the motor) and are mounting things onto the back of the motor (Honda CBR600 F4 motor cycle motor/trans) it makes things a bit more difficult. I guess if I was to go w/ trailing arms and mount them in front of the motor it might be a bit easier and also take some of the loads off the weak rear end?

Edit: I layed that out in SolidWorks which I have had good luck with. We have a copy of Adams Car (what the big boys use to symulate suspensions) but inputing the hard point locations is a pain!

77K5Blazer, I agree with you on fixing the buggy link to the frame with some type of ez-disconnects would solve the on road issue. I'm taking a carefull look at the whole idea again as there is a lot of potential. I sprotted a jeep today while on my way to work (noonish) with a trick idea as well. He had located what looked like a corvete independent rear leaf pack across from shackle to shackle as the shackle mounts with it fixed to the frame in the middle. I wonder how much binding would occur in the front of the leaf hinge from moving side to side at flex and droop.. and if it would promote more rear steer.

All this suspension talk is great but I think you guys are overlooking the biggest part of your suspension, the Shocks. I had a customer come into my shop the other day and he worked for Penske Racing Shocks and he said this is the most over looked part of the suspension. I think the reason everybody loves the link type suspension is because they spend the extra money and get the King or Sway-A-Way shocks for them and this is what makes the suspension. When I have the money by the end of summer I will finish installing brand new leafs on my Jimmy with a King or Sway-a-Way and it will work as good as a link type suspension I think. Just a thought what type of suspension won the last 2 out 3 years in the Top Truck Challenge? Is a Leaf type a better all around suspension? Just some thoughts to think about.

I think thats a great segway into talking about the Dampening factor. I like the idea of the King and the Bilsteins but 1/4 eliptical leaf packs and 1/2 eliptical with shackles at both ends are similarly efficient at storing energy. They all require you to locate the axle though. The shocks absorb energy which in turn restrics the springs ability to quickly store or release it. I say quickly because you can completely compress a spring slowly and store just as much energy with a shock as you could without a shock. Something you can adjust with the damping rate is the speed at which the suspension rebounds: if a truck with soft springs but hard dampers is pushed down, it will rebound very slowly, and a truck with stiff springs and light damping will rebound very quickly.You may not always be able to use the spring and damping rates you'd like, because of bumps. Small, high-frequency bumps require soft settings for both damping and springs. You can't use such soft settings for big, harsh bumps, because the truck would bottom out a lot, so you'll need to set your truck a little stiffer. Thats fine and dandy for desert racing, but what about rock crawling? Does a softer spring and a hard dampening rate keep you from slapping into rocks on the rebound or is this just theory?

This post is a bit confuseing to me, too meny conversations going on at once. (I like it, but a bit clutterd for me, needs to divided up some)

Scaned a couple of shots out of a G.M. Data book (just body dimensions/weights and junk), thought they might help someone.
Weights and Dimenstions:
http://community.webshots.com/storage/1/v3/4/33/67/36343367xmODKu_ph (http://community.webshots.com/storage/1/v5/4/32/95/36343295brWAgL_ph>http://community.webshots.com/storage/1/v5/4/32/95/36343295brWAgL_ph</a>
And)
I'm not sure if it'll help, but I thought it would be worth a shot.

BTW, I have others too. Suburbans, P/U, S10, ElCamino and even the Chevy LUV *hehehe*.

http://community.webshots.com/storage/1/v5/4/32/95/36343295brWAgL_ph

http://community.webshots.com/storage/1/v3/4/33/67/36343367xmODKu_ph

You have to remove the ".jpg" from the end of the url to link directly to webshots.

Ahhh, I see. You would think I would have that figured out by now, after the side pic thing.

Corrected the links, thanks!

Good addition to the post! I'm going to use it to completely model my truck in LightWave for some more fun.

I did a bit of filming today of my truck launching on flat pavement so I could see its reaction. Having the shackle flip on gives enough anti-squat to negate nearly all the rear end drop even with the axle wrap that I'm sure is happening (looking for a way to mount the camera under the truck to watch ... safely). I remember when I first got it how the back end would drop and the front end would rise when I took off from a stop and hadn't really noticed the change until now. I have a little bit of front end rise and other than that, flat launch. I did notice the back end drop when I lost traction while accellerating. Braking had a lot of front end dive and a lot of stored energy which rose then dropped and finally leveled the rear, to be expected.

Do you happen to have those measurements for 1st gen Blazers?

Nope, sorry. The book is for the '82 model year.

Roll center is something that I'd like to go into. Every vehicle has a front roll center and rear roll center which are independant from each other. The roll center is a theorectical point determined by the pivot point location and angles of the suspension linkages, about which the particulae end of the vehicle rolls. The roll center on a live axle and linkage type suspensions are dertimined a bit differently, this could be really usefull for everyone to get a handle on...

Front and rear roll centers are joined by a straight line running through the center of the truck called the roll axis. During conrnering, the truck will roll about the roll axis. The relationship between the center of gravity height and roll axis determines body roll taking place during conrnering.. The greater distance between the center of gravity height and the roll axis, the greater the body roll angle with a given lateral acceleration. A tight handling race car might have the front roll center lie 1-3 inches above ground and rear roll center lie 8-12 inches above ground. Ironicly, we often hear about having a high roll axis on a rock crawling truck, but what people are really refering to is minimizing the distance from the center of gravity to combat body roll. Interesting thought, if your roll axis was above your center of gravity, your truck would lean into a corner as opposed to leaning out of it!

Is the roll axis on a live axle calculated at the spring perch, or the line connecting the front spring mounting and the rear shackle mounting?

first by live axle I assume you are refering to a Hotchkis leaf sprung?
second there are many types of suspension that have a roll axis at each end rather then a nice clean roll centre.

I suppose you could use the Hotchkiss on an independent a-arm setup as well... interesting thought. I was refering to a hotchkiss, yes.

And please continue with the types of suspension which have more than one roll axis, it sounds interesting.

I dont know the correct name but what is being called 'SA link' on the other board looks to me to roll around 2 points.
diverging links on both upper and lower links for a 4 link, or diverging links and a panhard or other axle locating device will have 2 roll centres forming a roll axis.
look at the <a target="_blank" href=http://community.webshots.com/album/13190727rhRhHDXluW>chev power manual</a> and most of the examples have a roll axis.

hope the link works

I see what you mean. No matter which suspenion setup you use where more than one pivot point is involved in articulation, you have a roll axis associated with them. So in the case of the SA link rear and the S2 Link in the front, each having a roll axis, the vehicle itself will have a 3rd roll axis which is the average of the front and back, as the frame/body sees it since it cannot act upon one without effecting the other.

http://www.echobit.com/images/LEAF_3.gif

this is incorrect , i didnt no engineering but i sure know that when the top of the shackle is behind the lower one , the "loading " make it side really hard u got something mest up . im only saying this cuz i tested it out .

Yay! I've been waiting for someone to come back to it. Like BadDog again because I think he's right (and you of course). I'm running a forward shackle angle which feels softer than the 90* just like you have tested. Check these out...
http://www.dixiespeedway.com/leaf_spring_tech.htm
http://www.rpmnet.com/techart/leaf.shtml

I have read it so many times that I started to believe it myself. It's good to see people are reading all this! /forums/images/icons/smile.gif So where's BadDog, he shouldn't have given up so soon, I was ready to agree with him.

And for everyone else reading this far... feel free to chime in with questions or answers or anything else. I'm using this as a means to hash out all this stuff and make sense of it. The more minds that start to take this on, the further we'll get with working out what all this means when you add it all together and the quicker we'll cut through the eronious stuff!

Has anyone noticed any rear steer on their extra flexy rear leafs.. Marv Springer?

no no , what im saying is bottom of shackle ahead of top , BAD RIDE , has to literally lift up the truck when the spring extends . 90 or a tad behind is good . mine is a tad forward now , but im going to remove one more leaf from my custom packs and it should be good .

And I completely agree with you! I understood what you meant which is opposite of what the image shows.

Yes the rear does "steer" a little when it's fully twisted w/ my suspension. The flip causes a change in arc of the axle, and so during extreme droop the axle will move toward the transfer case. In fact a couple of guys who have installed my suspension have had to "shorten" their rear drive shaft if they had previously lengthened it for a block or spring lift. Anyway, it moves so far forward that the stuffed side appears to be "turning" toward the outside just a little bit. I've never seen it to be a problem though, and the added droop is definitely worth more than the little bit of steer.

One other thing I have noticed is that during full twist my suspension seems to keep the rear axle under the truck better than most 4 link systems I've seen. Purely by my observation, I've noticed that 4-link systems seem to "kick out" the rear axle toward the drooped tire when fully twisted. My FunBuggy even seems to do this - and this is why I dumped the "bench" back seat and elected to go with 2 small buckets back there. I really don't think this is good or bad.... just a characteristic of the 4 link.

Marv

Hehe, I thought you did agree with my statement about how the spring/shackle works, but were saying that I misinterpreted the drawings. Guess I read it too fast. /forums/images/icons/blush.gif Other than that I've just been reading. Most of the discussion has been about multi-links, roll centers, etc. and I don't really have anything to contribute, so I stayed out of it.

I have to say Marv, I consider your setup one of the better ones out there to date. It really takes advantage of the original design well. In fact, the only downfall is the moment from full droop to returning back to to center where the rotating shackle arm changes postion. Since it has no spring tension or binding to control its speed, the weight transfer could be exagerated if someone were to use too soft of a shock and they would have an over shoot and rebound scenario when settling the weight onto that spring. Frankly, thats a very small price to pay for all the benifits and driver control could do a lot to eliminate it! I had a discussion on another board this morning about locating the axle under the vehicle with various suspension devices. It seams realatively easy to construct a pan hard bar which could do just that and under flex keep the axle located, but if the whole back end were to drop(both sides) then you would have a shift in its position of to one side. Again, you overcome this well! Has anyone ever seen a Watts linkage on an off road vehicle for axle locating?
http://www.sierrarockcrawlers.com/data/srcforumuploads/watts_linkage_image_detail.jpg

Funny you should mention the swing arm return on Marv's suspension. I located my 5012s (generally known to be pretty firm) specifically to maximize their damping resistance to the swing arm load/unload cycle. They are roughly 45* to normal small axle/spring movements (almost vertical), so their damping rate is reduced allot. However, they are only about 20* off of inline with the axle movement at the point where the arm starts to swing down. They are also separated at the top allot more than most people are setting their long shocks. This was to help control body roll as well as further line them up with dramatic axle movements due to the Springer swing arm opening and closing.

BTW, Marv's typical setup does have a panhard bar. As for the watts linkage, there was a thread on PBB where a number of people posted links and stories about problems and breakage associated with the watts linkage. That’s about all I know…

Now thats some good info! I was going to relocate my shocks inbound at the top but woried about body roll. I guess the real saving grace there is that most shocks are a bit stiff anyhow! Good call on the mounting points!

I wonder what makes the Watts linkage os prone to breakage... its hard to sift through the BS over at POR sometimes.

Yes I have seen a Watts linkage on a offroad setup. Look at the new Range Rover they use it in the rear of it. I also seen it used on a 3 link setup on the front of a Jeep here in Denver. It look like it worked okay.

Where is the Roll Center on a Panhard setup? Is it at the mount where the panhard meets the frame or is it on the axle, or does it depend on the direction you turn?

where bar passes centreline of car

<a target="_blank" href=http://coloradok5.com/gallery/albuq67/aaa?full=1>http://coloradok5.com/gallery/albuq67/aaa?full=1</a>
Here is another example of the Watts link setup, that seems a little easier to decipher how it works. It looks to me like there will still be some side to side movement with the travel of the suspension, but not as much as the panhard bar.

After looking at both examples of the Watts link set ups, I can see that the design would not let there be any side to side movement, as long as the assembly is centered on the axle. As long as this design could be made bullet proof as far as durability, it should be far superior at locating the axle as opposed to a panhard bar. What is kind of hard to tell from the drawings, is that the ends of the links are both hooked to the frame, and it is the bolt in the center of the pivot that locates the axle, so that bolt is most likely the weak point, especially on a heavier rig. Hope you don't mind my couple of cents /forums/images/icons/wink.gif.

I agree, the panhard tends to walk the axle out the side of the vehicle with both tires dropped, not fun if you running fast down a road. I wonder if this is more of an issue of breakage with vehicles that don't have some form of solid axle locator which can completely control axle wrap. A Hotchkiss with this setup and no axle wrap control would probably break it.

<blockquote><font class="small">In reply to:</font><hr>

A Hotchkiss with this setup and no axle wrap control would probably break it.

<hr></blockquote>

Yes, but there is also arc travel with long travel links (3 or 4 link), so if there isn't any allowance for that in the watts pivot, then I would think that would make it prone to breakage as well. So essentially the watts needs to pivot in two directions to keep the stress on the pivot low.

the arms that go to the frame will account for any arc movement if you use hiems.
the breakage would be exactly the same as the bolts in a panhard rod
the only difference is the number of moving/wearing parts

<blockquote><font class="small">In reply to:</font><hr>

the arms that go to the frame will account for any arc movement if you use hiems.

<hr></blockquote>
I have built and worked on a couple of 4 link setups, and they do still have arc travel, especially in the long travel setups. It is not as pronounced as some of the swing arm setups on some desert racers that I have seen, but there is enough that it would place a lot of stress on the watts center bolt, unless the heims on both ends of the links allow enough flexability to compensate for it, but I am not sure, since I have only seen the watts setup working in my mind /forums/images/icons/wink.gif.

He's talking about the watts arms, I'm sure he is aware that multi-links still move the axle in an arc...

Oops, my mistake, I should have read mj's post more carefully.

also dont see why it would have to be centre'd to keep the axle square.
please elaborate your thoughts

If it is not centered vertically, the links in the watts would have to be different lengths. You could compensate for it by making the pivot arms different lengths, but if you offset the watts to one side of the axle, it will throw off the pivot point, making the axle swing in an undesireable manner when one side of the suspension is compressed. If it is not centered horizontally it will move the pivot point of the axle up (if the watts is on top of the axle, like the drawing I posted above). So if the suspension is compressed on one side, the whole axle will actually swing to the side based on the pivot location. The example of the watts mounted in the center of the diff cover would give the best performance, as single side suspension compression will pivot the axle from the center. So in theory, the axle will only move straight up and down, and pivot around that axis.

That other link took a dive.
I also updated the album with Chevy Truck specs/weight.

Just thought it might be helpfull -again-/forums/images/icons/smile.gif
<a target="_blank" href=http://community.webshots.com/album/36649130jkcUqN>http://community.webshots.com/album/36649130jkcUqN</a>

One thing with watts linkage the longer the travel of the vech. the longer the center link needs to be. Or the linkage will go over center. We ran this on the rear of our mustang for road racing. The problem on a off road vech. would be clearance of the lower arm mount from the frame.

I think they are on to us

I'm getting closer to a final design on the rear suspension. Just an updated peak.
http://www.echobit.com/images/a-link3.jpg

I had an idea on a shackle flip concept. How about mounting a large diameter short and stiff shock abosorber in place of the shackle itself. You'd have to encase it somehow so it wouldn't bottom out but it would extend slowly and retract slowly. If you gave it revolver characteristics you would have quite a little performer. I figure it would require a custom hanger and the stock one removed... might require a panhard bar to keep from applying any side load to it. anyway, just thinking out loud.

Why the bent linkes? Was that for more articulation? I don't think I would ever put bent links on the lower end (in compression during acceleration)...but I guess if you made them big enough it could work (but still not as strong as straight of the same size). Also me being the wuss I wouldn't want to trust my life to only 2 piviots to hold the thing together.

On second look the links are only bent in one plane and kept form any more bending by the tube down the middle...I still don't like bends.

The bends were a tough choice for me as well. They dont really need to be there at all for strength since the a link is fixed to the chassis at one end and fixed to the axle together at the other end and its all triangulated. I really felt that a little extra rigidity might assist in overall strength so I added them back in. The bend wont make that much of an overall difference. I decided not to go with johnny joints or heim joints but rather go with as large of a radius bushing setup as I can have custom made. The vibration dampening and full 360* range of motion made my mind up there, as well as the larger surface area and room for strengthening since the whole assembly is only attatched by two joints. I've found a few people who have built this setup and are quite satisfied both on and off the road. The biggest drawback was the distance the two a links had to be from each other to promote flex. This is why I chose to close the link a little early and tripple the link for the small remainder of the link. I'll go chrome moly for that center bar just to be safe. Now I'm working on the coil properties and dampening properties so I can start on the last of it.

I just finished uploading the animation as well...
http://echobit.com/catalog1.0.html

If shock placement is next you might like this
http://community.webshots.com/photo/20225580/36962747JQWhyp

I got that out of "The Shock Absorber Handbook" by John Dixon

Dan (Triaged)
Webshots is on to us, you have to link it the old-fashiond way./forums/images/icons/smile.gif

I don't understand why the Tri-angulated lower link is so popular. (please explain)

Some of the common factory set-ups for a 4-link was to tri-angulate the upper-link, (Chevelles). This set-up makes sense to me, the two lower links applie the forward forces straight to the frame, not at an angle.

BorregoK5,
If you would like to see that design in use check out this link;
http://www.sierrarockcrawlers.com/tech/projects/willys/projectwillys2.html

I agree.
on a car that a low roll centre would be desired OK
but
not on a lifted truck that needs a high roll centre

<a target="_blank" href=http://community.webshots.com/album/13188641pVktZEeClw>there is a pic of Sams suspension roll in this album if it links</a>

This link to the Willys was cool....! I've seen that rig several times in pics, but have never been close enough to see any of the details. Looks like it works really well...

The only "?" I could think about with this rear suspension design is I wonder if it has trouble with "straight up and down" travel. I mean, both "A" links are free to twist, but it seems that the bushings might provide some resistance to straight up and down.

Very interesting, though....

Marv

Yeah, Project Willy's used to be Project Slinky. I've been following his build and asking questions as he goes. In fact, if you go into their message forum, you'll see my suspension mockups in the suspension section under his posts.

Twizted, its really just about promoting flex and trying to locate the axle at the same time. With an upper a-link and straight links on each side for the lowers, you can only flex untill the outer lengths and their rotation start to promote binding and rear steer. I like the qualities of the dual a-links full rotation capabilites without binding at the links... untill they hit each other anyhow. /forums/images/icons/smile.gif