I've done the homework on here, searched, read, looked in the vehicle dynamics books, I even read through the "god of suspension" thread again. (I only thought it hurt the first time!) Still can't find what I'm looking for, so here it goes:

Does anyone have some input about anti squat percentages that have worked well for them? I've talked to the warn and RE guys and both seemed to think around 50% was good, and then built the kits around it. I've read here (and agree) that "a lot of anti squat is bad but a little is good". How about expressing some of this in numbers that can be transferred to another vehicle? Like a percentage.

I realize there are many other factors that matter in addition to anti squat, and the same percentages may not work best for every situation.

How about front "pro-dive" (for lack of a better term) when in 4wd? I know my truck likes to pick up about 6" under power braking in 2wd, and conversely will drop the front suspension several inches when I power brake in reverse but in 4wd I can barely get it to move. Obviously the front linkage (3 leading links) are pulling down on the frame enough to keep the rear end from picking it up. Anyone else play with this? (BTW, the rear is long leaves with under axle to under frame traction bars.)

Some examples that we can look at:
Radius arm traction bars (like sam's or m.o.r.e.'s and others)
Really flat 4 links/3 links, etc.
Thanks for any input.

It sounds like you are on the right track. IMO i'd say that 30%-80% antisquat would be desireable. Keep in mind that loading your rig up with gear will change the geometry, most likely decreasing the %age of antisquat.

How do you measure the percentage of antisquat?
I'm curious because I need to redo my rear 3 link suspension for less antisquat.

Thanks,
Mat

doesnt Lowes have an antisquat ruler?
they have everything

Originally posted by XTRMTOY
How do you measure the percentage of antisquat?
I'm curious because I need to redo my rear 3 link suspension for less antisquat.

Thanks,
Mat

OK Mat i'll do my best here. Hopefully this makes sense with no drawings. First you must find the instant center of the rear axle. This is done by plotting the point of convergence of the upper and lower links in the side view. Call this POINT A. Next draw a line, in the side view, perpendicular through the center of the wheel and the ground. Now take the point where the ground and the center of the wheel meet (call this POINT B) and draw a line connecting it with point A. Now draw a perpendicular line through the center of the front wheel to the ground. Now extend the line drawn from LINE AB to the intersection of the perpendicular line drawn through the center of the front wheel. Call this POINT C. Now the height at which LINE AB intersects the line drawn through the center of the wheel is compared to the vehicle's center of gravity. This will be expressed as a %age. This is the antisquat value. An antisquat value of 100% would mean that the CG and intersection point of LINE AB and POINT C would be in the same plane.

OK, get it????

What I've read in most suspension design books is that road cars are typically in the 15-25% range.

Admittedly that is not the correct bias but it gives an idea of what the "real world" uses.

Too much anti and the suspension will bounce instead of planting the tires down, no?

r@m

Originally posted by Root Moose
Too much anti and the suspension will bounce instead of planting the tires down, no?

r@m

Yep. Dude at ERoCC this past weekend was in a nice looking Avalanche rig. Cage was pretty, paint was nice, etc. Suspension had so much freaking anti-squat that every time he gassed it on an incline the rear walked under the rig and bounced the front end straight up in the air. He ended up rolling when he decided to stay on the throttle once. Looked good though:flipoff2:

Did the avalanche rig have all the joints for the rear end in a single line? I saw one of their buggies at EJS this year that could have run a single long bolt (all thread maybe) though all the link ends on the chassis, for front and rear suspensions. I would guess this is bad. Kind of like the radius arm traction bars a lot of jeeps use, all the power applied at one point.

For figuring percentage, read the above post, then check this
100% anti-squat: e/d = h/L
50% anti-squat: e/d = .5h/L

e = vertical distance from ground to instant center (where links would intersect if extended)
d = distance from rear wheel to instant center (horizontal)
h = center of gravity height
L = wheelbase
This comes from Gillespie "fundamentals of vehicle dynamics"

I too am guessing somewhere around 50% and maybe less would work well in keeping a rig stable on the steeps. I guarantee I don't want the rear end to jack up when I give it gas sitting on a nasty sidehill/uphill rock.

How do you get IC with parallel links since they never intersect?

OK Mat i'll do my best here. Hopefully this makes sense with no drawings. First you must find the instant center of the rear axle. This is done by plotting the point of convergence of the upper and lower links in the side view. Call this (A). Next draw a line, in the side view, perpendicular through the center of the wheel and the ground. Now take the point where the ground and the center of the wheel meet (call this B) and draw a line connecting it with point A. Now draw a perpendicular line through the center of the front wheel to the ground. Now extend the line drawn from LINE AB to the intersection of the perpendicular line drawn through the center of the front wheel. Call this C. Now the height at which LINE AB intersects the line drawn through the center of the wheel is compared to the vehicle's center of gravity. This will be expressed as a %age. This is the antisquat value. An antisquat value of 100% would mean that the CG and intersection point of LINE AB and POINT C would be in the same plane.

OK, i follw you, but one question. I am thinking that if POINT C were to be below the COG, then the percentage would be less, is that correct?? If so, is it less as a percentage of the hieght of the COG??

Originally posted by Pavemen
How do you get IC with parallel links since they never intersect?

If they are exactly parallel ingnore POINT A. Draw a line that is parallel to the links and that intersects POINT B. This will then dictate POINT C.

Originally posted by elf_cruiser


OK, i follw you, but one question. I am thinking that if POINT C were to be below the COG, then the percentage would be less, is that correct?? If so, is it less as a percentage of the hieght of the COG??

ELF-yes you are correct.

Use the equation POINT C (height)/COG(height)=X/100

right, that's what i was thinking... Thanks

Now for another kink in the equations:
Do we use the CG height for the sprung weight only or for the whole vehicle? That's probably not a big deal in a car with low unsprung weight but in our case where it's possible to have 1500lbs unsprung on a 3K# rig it's a pretty big deal.
I'm thinking it might have to do how much rebound you have in the front.
anybody else care to think about this or am I the only one?

One thing I have found that's practical and applies across the board is the instant center location vs. the 100% anti squat line. It's pretty easy to have a 1" difference in the mounting height of a link make a big change in how it reacts.

I guess that would indicate that either a lot of guys get lucky or this isn't very sensitive. A huge blunder is obviously bad though so I guess it's worth all this brain ache.

hmmm, good point stephen. I would assume that there is a correlation btwn the rebound characteristics of the front end, and the COG point, and it would have to be based on spring rate. Say for example(making this sh*t up as i type), that a spring rate of 300# per inch (x2 springs) means that if the sprung weight were 3000 lbs. then teh springs would be compressed 5 inches, right? So as they extend, less weight is held by them, but the unsprung weight is not yet being lifted by the anti-squat, until the springs have traveled up 5 inches, right??

Hmmm what does all this mean, I do not know...

I don't want to interupt the flow of this thread (which has been awesome) but it has brought up some interesting points about anti squat. I used to drag race with a Chevelle that ran 9.50's and we tried all sorts of things to make the car hook up and be consistent. We finally threw the book out and had a hair brained idea to put some 86" ladder bars on the car and do away with our traditional and "by the book" rear suspention. When we did this the car would hook so hard that we always crossed the 60' lights with the rear tires and always ran within 5 hundredths of a second and with the prevous set up we did good to hold it with in +/- .1-.15 seconds. I've always carried this idea over to my 4x4 projects but never have to this extreme by keeping the arms shorter than the CG. So was this just a freak occurance or what?

Originally posted by YELLER BLAZER
I don't want to interupt the flow of this thread (which has been awesome) but it has brought up some interesting points about anti squat. I used to drag race with a Chevelle that ran 9.50's and we tried all sorts of things to make the car hook up and be consistent. We finally threw the book out and had a hair brained idea to put some 86" ladder bars on the car and do away with our traditional and "by the book" rear suspention. When we did this the car would hook so hard that we always crossed the 60' lights with the rear tires and always ran within 5 hundredths of a second and with the prevous set up we did good to hold it with in +/- .1-.15 seconds. I've always carried this idea over to my 4x4 projects but never have to this extreme by keeping the arms shorter than the CG. So was this just a freak occurance or what?

86" Ladder Bars did I read that right?

Don't really know about the drag race thing, only thing I can think of is maybe you did something to make it more consistant through the longer arms? Maybe the tire contact patch was happier with less shock load? (I'm guessing it was a more gentle loading on the tire)
I know rear suspensions can be sensitive in cars, I had a stock car that ALWAYS wanted to drift into the wall on turn exits under heavy throttle. It was a 3 link/panhard rear and before one race my Dad just dropped the ride height by an inch and when I stomped the gas at the end of the turn it just took off with no drift. Not sure what that inch of height did since I didn't measure anything or know about this stuff but it made a difference for sure. Of course the arms were probably only 18" long at the most so there were pretty big angle changes through the travel. On our rigs with 40"+ arms it's probably not as big a deal.

Anyway, back to the subject at hand.........
I think you're right, if the front tries to lift it's going to act as though the CG was that of the sprung mass till you reach the rebound limit of the front suspension and then it will behave as if it has an extra 800# anchor under it.

Thanks Stephen and PIG.
I now understand how to figure it out.
I just took a bunch of measurements off my runner's rear suspension, took a good guestimate of where the CG might be and came out with an anti squat percentage of about 105%.
This percentage actually seems to work fairly well in mud and on level ground, unfortunately, it really makes the rear end jack when forward progress stops and you still give it gas. Definately needs less antisquat.
I will be re doing my link angles next week and will remount the links for about 50-60% anti squat.

Mat

Originally posted by XTRMTOY
Thanks Stephen and PIG.
I now understand how to figure it out.
I just took a bunch of measurements off my runner's rear suspension, took a good guestimate of where the CG might be and came out with an anti squat percentage of about 105%.
This percentage actually seems to work fairly well in mud and on level ground, unfortunately, it really makes the rear end jack when forward progress stops and you still give it gas. Definately needs less antisquat.
I will be re doing my link angles next week and will remount the links for about 50-60% anti squat.

Mat

Post some before & after pics when you are done.

You can actually see pics of the current setup at www.luker.on.ca/~titanic/utnl2002m.htm
I have the white 4 runner with the rear airbag suspension. As you can tell from the pics, the flex is not balanced at all. this will change when I do the front airbag suspension this fall.
If someone as a way to post them, I do have some video footage from that event.

Mat

Mat-
It looks pretty good. Though, when you redo the rear you may want to look at making the roll axis a bit flater. It looks like it would be a shit load of work though because it looks like the bags are attached to the links.

if you have access to scales you can calculate the CG hieght rather then guess it
there is instructions for this in the chevy power manual.
I have that in my webshots album if you need it.

PIG,
You're right about the airbags. I have them on the lower links to allow more height adjustment. For the links, I plan on lowering the A-arm diff mount by 2 inches and lowering the frame mounts for the lower link by another 2 inches as well. This should help bring the anti aquat down to a reasonable level and will place the IC about 250" in front of the rear wheels.

I have to admit though, I'm a little bit unsure I fully understand roll centre and roll axis. I tried doing some searches and read lots about it, but did not find a really good explanation of what to shoot for.
Care to give a good explanation of roll centre, roll axis and how to optimize it?

Thanks,
Mat

Originally posted by XTRMTOY
PIG,
You're right about the airbags. I have them on the lower links to allow more height adjustment. For the links, I plan on lowering the A-arm diff mount by 2 inches and lowering the frame mounts for the lower link by another 2 inches as well. This should help bring the anti aquat down to a reasonable level and will place the IC about 250" in front of the rear wheels.

I have to admit though, I'm a little bit unsure I fully understand roll centre and roll axis. I tried doing some searches and read lots about it, but did not find a really good explanation of what to shoot for.
Care to give a good explanation of roll centre, roll axis and how to optimize it?

Thanks,
Mat

There used to be a good diagram explaining how to calculate roll axis. I went and looked for it on the God Of Suspension thread. Gordon posted it but it is not there anymore. So, Gordon if you read this put it up man.

Originally posted by PIG


OK Mat i'll do my best here. Hopefully this makes sense with no drawings. First you must find the instant center of the rear axle. This is done by plotting the point of convergence of the upper and lower links in the side view. Call this POINT A. Next draw a line, in the side view, perpendicular through the center of the wheel and the ground. Now take the point where the ground and the center of the wheel meet (call this POINT B) and draw a line connecting it with point A. Now draw a perpendicular line through the center of the front wheel to the ground. Now extend the line drawn from LINE AB to the intersection of the perpendicular line drawn through the center of the front wheel. Call this POINT C. Now the height at which LINE AB intersects the line drawn through the center of the wheel is compared to the vehicle's center of gravity. This will be expressed as a %age. This is the antisquat value. An antisquat value of 100% would mean that the CG and intersection point of LINE AB and POINT C would be in the same plane.

OK, get it????

Pig, from your description I was unclear on how eaxctly point C was determined, so I made 2 :emb3: I think you meant point C1... and by the way, in the interest of making things clearer, I drew us a suspension with a shitload of antisquat. :D

Originally posted by TNToy


Pig, from your description I was unclear on how eaxctly point C was determined, so I made 2 :emb3: I think you meant point C1... and by the way, in the interest of making things clearer, I drew us a suspension with a shitload of antisquat. :D
Nice drawing, i'd say you are looking at about 200% antisquat.

Originally posted by PIG

Nice drawing, i'd say you are looking at about 200% antisquat.

So you would divide the height of the COG by the height of C2 to get the %? (or is it C2 by COG)

Originally posted by bigdude


So you would divide the height of the COG by the height of C2 to get the %? (or is it C2 by COG)

Dude- yes,

One more time Use the equation POINT C2 (height)/COG(height)=X/100

solve for X

Originally posted by PIG


Dude- yes,

One more time Use the equation POINT C2 (height)/COG(height)=X/100

solve for X

Sorry, didn't read the whole thing. just looked at the drawing and posted:flipoff2:

I'm not sure about the rest of you, but the CG on my vehicles is NOT over the front tires. To find the correct CG you need to weigh the truck. Total weight, and rear(or front) weight. The CG location will be , for example : 4000lb total, front weight 2500lbs , with a whelbase of 100" = 62.5%weight on the front. So the CG will be 62.5" from the rear wheel centerline. Fo cars the CG height is roughly the height of the camshaft centerline, remember I said roughly. The anti squat percentage is where the line line from the tire thru the IC crosses the CG vertical line. If the CG is 30" above the ground, and the line crosses it at 24" you will have 66%antisquat.
I believe I am correct on this. Please corrct me if my thinking is off.
Thanks, Phil

Originally posted by indysand
I'm not sure about the rest of you, but the CG on my vehicles is NOT over the front tires. To find the correct CG you need to weigh the truck. Total weight, and rear(or front) weight. The CG location will be , for example : 4000lb total, front weight 2500lbs , with a whelbase of 100" = 62.5%weight on the front. So the CG will be 62.5" from the rear wheel centerline. Fo cars the CG height is roughly the height of the camshaft centerline, remember I said roughly. The anti squat percentage is where the line line from the tire thru the IC crosses the CG vertical line. If the CG is 30" above the ground, and the line crosses it at 24" you will have 66%antisquat.
I believe I am correct on this. Please corrct me if my thinking is off.
Thanks, Phil

Indy-Ok who said the CG was over the front tires?

This statement is wrong The anti squat percentage is where the line line from the tire thru the IC crosses the CG vertical line.


I am looking at the drawing again and was wrong with my suggestion of 200% antisquat. For some reason (brain Fart), I thought that A was the horizontial plane that represented the CG. There is NO CG point on the drawing unless TNT made POINT A the IC point as well as the CG Point. If this is the case for representation purposes then 200% is about right. It (CG Point) sems a bit low though.

Originally posted by PIG


There used to be a good diagram explaining how to calculate roll axis. I went and looked for it on the God Of Suspension thread. Gordon posted it but it is not there anymore. So, Gordon if you read this put it up man.

OK I found it. Thanks Gordon!
http://www.sierrarockcrawlers.com/data/srcforumuploads/test.gif

The diagram looks good PIG.
Is the roll centre point B? I'm pretty sure it is.
Now for the roll axis, are you connecting point B (the roll centre) to the top mounting point of the lower links or to the imaginary line where they would cross? If it is the imaginary line where they would cross, what point do you use if your lower links are parallel to each other and will never cross?
What kind of the roll axis should we be aiming for when it comes to a rock crawler?

Mat

Originally posted by XTRMTOY
The diagram looks good PIG.
Is the roll centre point B? I'm pretty sure it is.
Now for the roll axis, are you connecting point B (the roll centre) to the top mounting point of the lower links or to the imaginary line where they would cross? If it is the imaginary line where they would cross, what point do you use if your lower links are parallel to each other and will never cross?
What kind of the roll axis should we be aiming for when it comes to a rock crawler?

Mat

Yes, the rear axle rotates (RC) about point B. Yes, to get the roll axis, connect A and B. If the lowers are parallel the draw a line that is parallel to the lowers but that intersects the RC, point B. This would be the roll axis.

Pig,
I think what is throwing me is in the diagram from a few post back from TNToy, and what you said in one of your first posts :Now draw a perpendicular line through the center of the front wheel to the ground. Now extend the line drawn from LINE AB to the intersection of the perpendicular line drawn through the center of the front wheel.
The line thru the FRONT wheels is not correct unless thats where your CG was. It should be a line, perpendicular to the ground that runs thru the CG. That is where the antisquat(normally called percentage of rise) is found. Everything else you have said is correct.

what part will spring rate play in all of this

Originally posted by indysand
Pig,
I think what is throwing me is in the diagram from a few post back from TNToy, and what you said in one of your first posts :
The line thru the FRONT wheels is not correct unless thats where your CG was. It should be a line, perpendicular to the ground that runs thru the CG. That is where the antisquat(normally called percentage of rise) is found. Everything else you have said is correct.

Don't believe me????? Look in the Millikin Book.

Originally posted by frankie fountain
what part will spring rate play in all of this

Very little unless have SQUAT.

Spring rate doesn't have anything to do with link geometry and how it will behave. However a link type suspension will behave differently based on ride hight(spring height). Let's just say that you build your four link and it's all good, then you want to run bigger tires so you put a taller spring in there. All of a sudden your Instant Center is a lot higher and the Roll Axis is steeper. I'm not posative, but I think this will produce more anti-squat.

what part will spring rate play in all of this

I think he means front spring rate. Clarified - How do we weigh the front end when calculating COG??

Option 1- Calculation based on curb weight of sprung+unsprung weight...

Option 2- Calculation based on ONLY sprung weight, because the unsprung weight of the front end doesn't affect the anti-squat until springs are fully extended...

As i said earlier, i don't know what this means, but i'm sure it has some relevance...

Pig,
I do not know of this book you recommended. I'm not a book educated man in these things, only some real world experience. Built ProStock chassis for Hansens Racecars, Some Indy Lights suspension work for Twister Racing. If you look in the Alston Chassis works book, it shows as working off of the CG, and not front wheels. So now we have 2 books that say diffrent things. I would lean towards the suspension working off of the CG rather than the front wheel centerline. Guess thats just me. Is that book available at the bookstore at CalPoly pomona you think?
Thanks, Phil

Originally posted by indysand
Pig,
I do not know of this book you recommended. I'm not a book educated man in these things, only some real world experience. Built ProStock chassis for Hansens Racecars, Some Indy Lights suspension work for Twister Racing. If you look in the Alston Chassis works book, it shows as working off of the CG, and not front wheels. So now we have 2 books that say diffrent things. I would lean towards the suspension working off of the CG rather than the front wheel centerline. Guess thats just me. Is that book available at the bookstore at CalPoly pomona you think?
Thanks, Phil real world experience ! this is what i understand to we have built many 4 link machines and have come to a formula for standerd 4 links .and we are experamenting with reverse 4 links. if the link system is as ours .we can change the traction of the machine with spring rate.and the roll over rate by spring bias front to rear .meaning if it rolls over back to easy we use stiffer rear spring rate or vise versa. i'm trying to understand what you all are saying so dont attack my ways as i know they work becaus we have many machines running trails now.but if you all may make me see somthing better then do it. if i can learn better info that is real world then my mind is open.;)

frankie,
By reverse 4link, do you mean the links for the rear end will be going backwards? like, attached to the rear bumper area? this is interesting if thats what you are doing. Only prob i would see would be departure angle. I learned alot about working on cars in school(degrees in Automotive and racecar technology..woohoo..all BS just papers), i learned how to do things correctly in the real world at various jobs. I trust the " do it and find out if it works" theory way more than any school books.
Phil

No, he doesn't mean that. He's referring to a term he used in this thread:
http://www.pirate4x4.com/forum/showthread.php?s=&threadid=66343

the revers 4 link is a flipet up side down std. 4link and the locating V is turned around.the outer bars go straight .
dr.evil thank you for the complament. and pics.the reaper has seen a few improvments since last time you saw it .stiffer springs and fox 4'' travel hyd. bump stops .also installed a sway bar for road use.and rear mounted lt1 distribter .and vortech super charger .

IVI will work,if rear steer is a problem for you i suggest a revers 4 link this system keeps the long links flater .the flater the links are the less they arc from axle location .this means les steer .in the picturs that twisted posted of the reaper the link system is a revers 4 link with 14'' sway aways my travel is 9'' up travel 5'' down at shock with 1/2'' axle steer under fuul articulation . and the links are out of harms way. this system also puts four heims at impact point.wich is the axle.this system is still under reserch and testing.back to the standerd 4 link you must parallal the lower link with drive shaft or stay close .and if this puts the links at lots of angle it will steer more if the shaft angle alows flat or cloes to flat angle steer will be less.need more info or think im crazy let me know i already know i am crazy so keep that to yousef hey twisted thanks

He has actually used this, by the way. Here's a shot of his Reaper's rear suspension:
http://home.off-road.com/~mithrandir/trails/04-28-02/1047.JPG

Originally posted by indysand
frankie,
By reverse 4link, do you mean the links for the rear end will be going backwards? like, attached to the rear bumper area? this is interesting if thats what you are doing. Only prob i would see would be departure angle.It could be done, though.

If Walker Evans can run a leading-link front end, then you could probably make a trailing-link rear work...
http://www.4wheeln.com/arcafinals2001/images/walkeronside.jpg

Ok, now I understand what was meant by reverse 4 link. Thanks TNToy.

Originally posted by indysand
Pig,
I do not know of this book you recommended. I'm not a book educated man in these things, only some real world experience. Built ProStock chassis for Hansens Racecars, Some Indy Lights suspension work for Twister Racing. If you look in the Alston Chassis works book, it shows as working off of the CG, and not front wheels. So now we have 2 books that say diffrent things. I would lean towards the suspension working off of the CG rather than the front wheel centerline. Guess thats just me. Is that book available at the bookstore at CalPoly pomona you think?
Thanks, Phil

Here is the Millikin Book (http://www.sae.org/servlets/productDetail?PROD_TYP=BOOK&PROD_CD=R-146)

Look at page 619 Figure A.

OK, few things here:
1: Let's not let this degenerate into a book learning vs. build and try design debate. A lot of good stuff has been built without knowing just what you're doing but it can be enhanced by understanding more of principals behind it. (go read the book and try to apply it to what you know) On the other hand, no one sitting around with a book in hand it going to truly have a handle on any of this without driving a truck they built with the stuff they learned, it all goes hand in hand. So let's leave this one alone or start another thread for it.

2: I think there's a little confusion on the anti squat calculations. The way I'm reading it is that the SLOPE of the line from the contact patch to the instant center should be compared to the SLOPE of the line from the contact patch to the CG HEIGHT over the front axle. This is just basic rise over run, nothing more. There's some question as to what CG height to use (include unsprung or not), and nobody here knows exactly where the CG is vertically yet so that part's still a guess but you have to start somewhere.
If your CG height is about 40 inches and you have a 100" wheelbase, your 100% anti squat line slope would be 40/100 = .4. For you to have 50% anti squat you would have to have a line slope from the rear contact patch to the IC of the rear suspension of .2. Notice this is a line slope, not a location. Your IC could be 20" off the ground and 100" forward, or it could be 40" off the ground and 200" forward, or could even be 10" off the ground and only 50" forward. YOU CAN'T COMPARE THE IC HEIGHT AND THE CG HEIGHT DIRECTLY.

As for freddy controlling the way the vehicle acts with spring rates, it does work, depending on a lot of stuff. A hill will always transfer the same amount of weight on the chassis but with soft springs it may really squash the end that's down hill and that could change the link geometry and maybe other stuff too. We have a LOT of factors to look at in the vehicles overall performance. What we don't want to do is have to use bandaids for something that could be better fixed with a better overall suspension design.

I have some more playing around to do with link locations on my rig but preliminary sketches look like I'm going to end up around 70% anti squat, so I hope that works!

You know all these calculations and theories are all fine and good...but it's one thing to figure out the "perfect anti-squat" figures and what not but how do you plan to apply those to your vehicle? It's not like you can use an imaginary point to help you align some brackets when your welding them on! Sure it may give you an idea, but come on! The only way your gonna get something to work like you want it to is to build it and THEN change what you dont' like about it. The bottom line is that it's not very likely that your gonna be able to apply all that fancy math to a suspension that's gonna fit on your rig. Oh ya, before you go jumping all over me saying that I dont' know shit, YES I have built a four link suspension for my Jeep. I learned alot in the process and even more from this web site. Fab on ;)

HA...........yes this is the pirate board I remeber. Its gettin good now......

who is freddy my name is frankie ?the math may be ok but im not that smart so i experiment shit i cant even spell if you understand the math and thearys great go for it you need no help .if any body wonts my formula ask me and i will try and tell you it works for us and if i find somthing better then i wiil change it.i am not hear to be a asshole but if i can help then im hear;)

Sorry Frankie, brain fart as usual.
Stephen, there is a way of calculating exactly where your CG is. Once youve weighted the truck level on the ground (total,front, rear weights) you then get the same measurments with the rear end raised 12 to 24 inches(higher seems to calculate out more accurately from whatI remember).Then its a formula, that I havnt found in my pile of papers yet. A bit complicated, but at least it can be done.

Originally posted by Stephen

2: I think there's a little confusion on the anti squat calculations. The way I'm reading it is that the SLOPE of the line from the contact patch to the instant center should be compared to the SLOPE of the line from the contact patch to the CG HEIGHT over the front axle. This is just basic rise over run, nothing more.

This is wrong. You are not comparing SLOPES. TNT's drawing is on the money if the horizontial CG plane intersects point A. Then C1 over C2 X 100 to = %.


Originally posted by Stephen
What we don't want to do is have to use bandaids for something that could be better fixed with a better overall suspension design.


Yes.

This is a good thread I've enjoyed following. A few things that I've been thinking about along these lines...

The way I visualize anti-squat is how badly the rear wheels want to walk up in under the rig. As the rear tires push forward, they take more load (as has been implied)...is this a good thing or bad thing for wheeling? Also - designing for it is very difficult because our vehicles are never at 'normal' ride height. Uphill, downhill, articulating, all change the geometry substantially. What do you guys feel is the best case to design for? I'm leaning toward uphill climbs, though the worst situation seems to be having the front end stuffed in a hole with the back unloaded. I've seen a few pics of the rear axle actually walking under a 4X in cases like this.

Also - antisquat is caused by the rear tires trying to propel the vehicle and most books focus on 2WD applications. As mentioned in one of the earlier posts, in 4wd with the brakes on you get no antisqaut...this is becase the rear wheels are essentially aplying no forward force. When in 2wd, typically the front brakes hold you back thus force is transferred through the links & frame to the front tires. Why am I hung up on this? - Becuase the only time antisquat will come into play for a 4WD is when the rear tires are producing more tractive force than the fronts. In these cases I can't see where putting more load on the rear is beneficial. The rigs with less antisquat seem to work better because they stay more balanced in all situations.

Once last note - the Walker Evans front link effectively serves to provide antisquat to the front end. When it has traction, the front end will actually pick up load by that link. (Again think of what happens if the axle can walk forward in the vehicle)

I don't mean my comments to start a pissing contest and degrade the thread, so if you don't like them post some reasons why or just keep trying to lick yourself.

Sorry Frankie, guess I lost it in the heat of typing!

Once again I'm not going to get into the "design by trying first or design on paper first". Do what you want, that's another thread. If you don't want to lay your suspension out on paper and try to figure this out, don't. For those of us that are interested, we'll keep trying to figure it out. I would like to have the input from the guys that have vehicles that work but for your input to help us out, we need to have the numbers.

RE 87YJ: You're right, our rigs are seldom in the same suspension position, it's another big variable.
I think the consensus is that a lot of antisquat is bad for most situations since it does cause the rear to walk under the rig in some situations, and generally we don't want a truck to raise up (raising the CG and rolling us over) under any conditions. It also seems like you can put large shock loads on the tire patch if it grabs too hard. There probably is a good bit "works well in one kind of terrain and not in another", just like most other stuff on a vehicle.

indysand, I have played around with calculating CG heights before and it was a pain. Not impossible but there are definitely techniques that help. We had to pick the truck up a long way to get a meaningful change in the weights (like 45 degrees or more) and block/chain the suspension solid. This is where we get into deciding if we use the front weight sprung or unsprung.......
It was also important to keep the line lifting the front of the truck exactly vertical so that it wasn't pulling it a different direction, like off the scales.

pig, maybe we're talking about the same thing in different ways? I'll have to go back and look at the posts more closely since putting all this in text is a pain to understand. My vehicle dynamics book basically uses slope to relate the percentages. I explained it some in one of the earlier posts on this thread using their terminology. I'm pretty sure that the first thing we have to do is figure out exactly how to figure our percentages before we can measure and compare them!

I ran leading links on the front of my tube chassis mud drag car yrs ago- I know i'ts not rock crawling but I felt it really helped the launch in this situation.

Walker is no longer running leading links on the front, they were trailing in April when i saw his car at Pro rocks.

We need some laymens terms- my heads still spinning so correct me if I'm wrong.

1) Reducing upward angle of upper rear arms(lowering front mts or raising rear mt) lowers IC and moves it rearward= less antisquat?

2) moving rear axle back with same geometry moves IC rearward, shifts CG forward and reduces anti-squat??

3) unless we stand the rig on end we'll never know what height the CG is- could it be calculated by bring the rig to the rollover point with a fork truck/winch cable etc? what are some tricks people have used.

4) you want some anti squat for traction but no so much that the suspension cycles and hops?

5) supersoft long suspensions will really confuse the mess (much more compression on the tail when climbing while the front unloads and get's 6" or more taller.)


6) sounds like we really don't "need" exact figures- only to know what approaches one can take to reduce it (most often) or in some cases increase anti squat.

How about some help with verification on these points or some more laymens terms?

Don't have time for much more here but to clarify some of the calculations, Pig's technique for figuring anti squat (milliken) and my technique (gillespie) give the same results. Graphically, Pig's is a little easier to see but they come to the same conclusion.

ok im tring to build a SA-link style suspention for the rear of my 4runner, I know my roll center will be parallel with the ground but my links are gonna be parallel with each other so how will i find point A?

Originally posted by PIG


If they are exactly parallel ingnore POINT A. Draw a line that is parallel to the links and that intersects POINT B. This will then dictate POINT C.

ok but i dont understand that, here is a pic, the only point i can find is point B which is the red dot. The red line is the roll center and the blue lines are the links. can some one tell me were to find C1 and C2? Thanks.

Draw a line parallel to the links passing through the red dot at your tire contact patch. Where that point intersects the front axle centerline is the calculation point for the squat calculation.

ok i drew a line like you said and it looks like i would have very little anti-squat. now where is C2?

I know this is an antisquat thread, but to go slightly off topic....when designing a 4 link, how do you determine whether or not you will have rear steer, and how much? Do you just have to cycle the suspension and find out, or can you look at a drawing and see it?

Originally posted by blay127
I know this is an antisquat thread, but to go slightly off topic....when designing a 4 link, how do you determine whether or not you will have rear steer, and how much? Do you just have to cycle the suspension and find out, or can you look at a drawing and see it?

It is based on the roll axis. Draw a line, from the side, through the converging point of your upper links and the converging point of your lower links. If the line is perfectly level you will not have any roll steer. If your lower links are parallel and your uppers converge, then the roll axis goes through the converging point of the uppers and is parallel with the lower links.

Search for roll steer, reverse 4 link, and read the "God of suspension" thread. I think everyone should have to shovel their way through that thread before they link up a rear.

Back to anti-squat....

So,
If I understand this correctly, if the lowers converge at the frame, and the uppers are flat/nonconverging. Then,
- there is no rear steer, because the roll axis is level,
- the "anitsquat line" is no higher then the converging point of the lowers.

So, it seems that the forward attachment of the lower links could all be on the same axis, and keep the pinion pointed at the transfercase yoke. Instead of mounting the forward attachment of the uppers up higher, like I see on most suspensions.

Or, am I totally forgeting something?

Thanks,

Dang, please ignore that previous post. I don't want to confuse anyone.

I've seen several people run rear suspensions with the lowers converging at the chassis. I'm trying to decide if it is better to converge the uppers above the rearend (can't remember who it was), or non-converging uppers (like Camo's).

After reading PIGS comments 4-5 times, and trying to find any useful info in Herb Adams "Chassis Engineering" book, i still can not figure out the roll center, or the IC, for Camo's link setup.

What are the pro's/con's of converging/non-converging uppers, when the lowers converge at the frame?

I guess I'll go punish myself by reading god of suspension AGAIN!

:eek:

I think I figured out the difference between the "Camo" suspension, and the double XX setup.

The camo suspension has more rear steer, but controls body roll better under power. Obviously not enough, since there was a pic of camo upside down in his backyard.

The "Myrearlink.jpg" XX has less rear steer, and has more body roll under power. Seems like the roll axis is easier to level, but I haven't figured out the roll axis equation for camo's setup.

Anything else, or more answers? Please!