I went through the recent antisquat thread and pulled a couple formulas, but must be mis-applying them - and was hoping someone could straighten me out on it! Here's what I've got:

Height of rear axle instant center = 23.75" (very low)
Distance from the rear line (perpendicular through the rear wheel) to the point of instant center, horizontal component only, = 38"
Overall wheelbase, 109"
CG height = 35" (approximated about 1.5" above the crank)

Using e/d = x*h/L I come up with .625 = x * .32

(where x*100 = antisquat percentage)

...this comes out at almost 200%!!! I MUST be figuring something wrong here, the IC is very low and the links are about 38" and virtually parallel to the ground (upper links actually have 2 1/2 " of rise up to the axle-side mount!); it doesn't seem remotely possible that the antisquat % should be so huge!

Pig, Elf, anyone else, would you do me a big favor and let me know what's up with my equations?

Also, along the same line, this rig is 70/30 weight split, any suggestions on what % anti squat I should shoot for approximately?

Thanks a ton you guys, we are trying to finish up the rear suspension tonight!!!

NOTE: the equation above was posted in a reply to Stephen's original post... (see below for quote from that post)
--------------
"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" "
---------------

yeah, i come up with 194% as well. You are using the formula given by stephen near the top of the thread. I would suggest trying PIG's way, and see what that result's in. 200% doesn't sound right based on the info you provided. I think that may be a formula good for cars, but not 4x4's, as he said it came from a book.

Good Luck!

Like I said formulas suck:flipoff2:

OK I ran the math..........249%
Lets double check something here. Look @ TNT's drawing. Your A to B distance is 38" , yes? Also, Look at point A. This is your IC point 23.75" (height) , yes? Ok so I got a C1 value of 87.267" and a C2 =CG (intersection) = 35" Care to double check anyone?

Beartrack- Do you have some pics of your set up, a visual may explain some stuff.

Hi Elf and Pig. Ug. Yes, you are correct on all figures Pig, the only caveat being that my A -> B length of 38 is only the horizontal component, I am assuming that's the way to measure it. If it is the actual length of line AB, then it's 45.5-ish. Do you know which figure would be the correct one to use?

So I am assuming that this setup is going to be WAY prone to jacking going uphill, correct? Man, we just finishe a complete tear down of the old suspension to build this, and then I ran across this thread. Hate to think we wasted all that work... yet again :( :rolleyes: :(

Originally posted by desertCJ
Like I said formulas suck:flipoff2:

especially formulas that are wrong! actually that formula I think comes from Carol Smith, and although it is technically not correct it serves the roundy round guys well enough, because it is much simpler than the totally correct formula. To get it right just go back to the engineering statics equations or the Miliken book.

But the equations are pretty complicated so I won't bother especially since I can't post a good picture anymore, and most of us don't have good data to plug into the equations anyway.

Here is the method theat will get the job done. Basicaly you draw the line fromt he tire contact patch through the intersection of the links just like on TNT's drawing. This would be his line from the bottom of the tire to point C1. If this line passes through the CG then you have exactly 100% anti squat. If the line passes above and to the right of the CG then you have more than 100% anti squat. If the line runs below and to the left of the CG then you have less than 100% anti squat. If the line runs along the ground (intersection of links on ground) then you would have 0% anti squat. if you draw up the scale drawing you can guess if you have 50% antisquat or 75% based on how the line is positioned between the 0% line and the 100% line, and that is plenty close anyway because you are only guessing at the CG location.

My guess is if you recalc this way you will be close to 100%

so you can see you need to know not just how high the CG is but how far forward and backwards it is located. since you said 70% of the weight is on the front wheels the CG would be located 70% of the wheelbase forward of the rear axle. Your height estimate sounds reasonable, when calculating antisquat it is best to error on the side of designing in too little so estimating a CG on the low side would be safe. (I usually use the camshaft height rule of thumb)

In my opinion what you want in terms of antisquat is as much as you can get at full compression and less than 100% at full droop.
This can be acomplished with very long lower links and shortish upper links, where the upper and lower links are close to parallel to each other at ride height. This way in extreme droop the intersection of the upper and lower links is actually behind the rear axle, but that is OK antisquat is still calculated the same way. You will see this type of geometry on desert rigs that do well and on ARCA rigs that do well, and the theory says it should work well.


If your real anti squat number when calculated correctly is more than 100% you will have a problem with the rear end trying to walk under the vehicle climbing a hill. This is comonly and effectively bandaided with a center limiting strap. but you might as well build it right.

Here is how to find your center of gravity, thanks to Daless2.

http://www.pirate4x4.com/forum/showthread.php?s=&threadid=47834&highlight=COG

CYA!

Originally posted by Beartrack
Hi Elf and Pig. Ug. Yes, you are correct on all figures Pig, the only caveat being that my A -> B length of 38 is only the horizontal component, I am assuming that's the way to measure it. If it is the actual length of line AB, then it's 45.5-ish. Do you know which figure would be the correct one to use?

So I am assuming that this setup is going to be WAY prone to jacking going uphill, correct? Man, we just finishe a complete tear down of the old suspension to build this, and then I ran across this thread. Hate to think we wasted all that work... yet again :( :rolleyes: :(

OK that is why it was so off before. I thought that 38" was AB. I ran it again and got 191%.

Gordon-
Could you calc antisquat % from comparing the slope of the line AB (reference TNT's drawing) with the slope of the line (COG)A?

I think this is what Stephen suggested. It makes sense.

easy to understand antisquat diagram (http://community.webshots.com/photo/19011079/30642696abWUZlmXsO)

formulas rule, way easier to copy what someone figured out works then doing it wrong everytime

Scott, just finish the thing. If you designed it like we talked about then it should work fine. YOU THINK TOO MUCH! Remember, it's thinking that screwed it up the first time.

It's not like you REALLY know where the CG is anyway.

Don't make me come down there! :)

if you can scale the truck you can find exactly where the CG is.
it is a simple FORMULA.
why is thinking so hard for some?

You might be able to find the CG horizontally (front to back) but what about vertically?? Huh? Huh? That's not so easy now is it?

Originally posted by Toyman
You might be able to find the CG horizontally (front to back) but what about vertically?? Huh? Huh? That's not so easy now is it?

Sure it is. Pick it up by the back tires, and mark the side of it with a sharpie right as it flips over forwards. Stupid.

Originally posted by mj
if you can scale the truck you can find exactly where the CG is.
it is a simple FORMULA.
why is thinking so hard for some?

damn...if I had a buck for everytime I've witnessed over-educated people use thier "thinking" to arrive at a wrong answer I'd be retired...

on a serious note...something that's been bugging me for a while...just how applicable are formulas and theories that have been derived for designing short-arm short-travel race car suspensions to the long-arm extreme-travel suspensions used on our rigs?

Originally posted by Toyman
You might be able to find the CG horizontally (front to back) but what about vertically?? Huh? Huh? That's not so easy now is it?

http://members.aol.com/sccacuda/cars/4SmthTa.html

Originally posted by TNToy


Sure it is. Pick it up by the back tires, and mark the side of it with a sharpie right as it flips over forwards. Stupid.

ummmm...he was talking axial CG...

Axial? Which axis, exactly?

You need it in three dimensions. Left-to-right (probably isn't, but is assumed to be) in the center of the vehicle. They've already covered it's presence front-to-rear. That leaves it's height. By marking the point at which the vehicle would endo along the vertical line marking the front-to-rear CG, you *could* isolate the third dimension.

Sure it's a retarded method to do it, but that's why it was a joke.

Originally posted by 333J

on a serious note...something that's been bugging me for a while...just how applicable are formulas and theories that have been derived for designing short-arm short-travel race car suspensions to the long-arm extreme-travel suspensions used on our rigs?

Why would the pricipals be different?

Originally posted by Gordon

In my opinion what you want in terms of antisquat is as much as you can get at full compression and less than 100% at full droop.
This can be acomplished with very long lower links and shortish upper links, where the upper and lower links are close to parallel to each other at ride height. This way in extreme droop the intersection of the upper and lower links is actually behind the rear axle, but that is OK antisquat is still calculated the same way. You will see this type of geometry on desert rigs that do well and on ARCA rigs that do well, and the theory says it should work well.


If your real anti squat number when calculated correctly is more than 100% you will have a problem with the rear end trying to walk under the vehicle climbing a hill. This is comonly and effectively bandaided with a center limiting strap. but you might as well build it right.

Good info Gordon. I definitely have been wondering how all this could be accurate without figuring in the front-to-rear COG. Didn't seem to make sense that it wouldn't figure in. Your points make sense, however my concern with your thought that short upper links and longer lower links (close to parallel with each other especially) is that under droop it would drop the pinion into the rocks, correct?

Thanks for the great info everyone - and Toyman, YES you are going to have to come down here - and help us finish this beast up! :p

You might be able to find the CG horizontally (front to back) but what about vertically?? Huh? Huh? That's not so easy now is it?

not too hard either
you can find the actuall CG, that means vertically as well as horizontally.
but that would be using a formula :rolleyes: wouldnt wanna try that

you wiegh the axles then raise one end to a set angle, then rewiegh the axles, plug numbers into formula and jus' like magic you have the CG

Okay again, here is a direct link to one of our member's method of finding your COG.

http://www.jeepaholics.com/tech/cog/#_Toc535118719

The member is Daless2 you can PM him for more info.

Originally posted by PIG


Why would the pricipals be different?

why would they be the same?? with 3 inches of total wheel travel you may be able to (hypotheticly) design a system that optimizes a characteristic, let's say anti-squat, and ignore the negligable negative characteristic, let's say rear-steer...apply the same design with 30 inches of wheel travel and you're driving sideways anytime you flex...

again, this is all hypothetical, I'm still trying to understand the principles, and this is something I keep tripping over...

Not sure what to use for a formula now. Gillespie's derivation seemed pretty sound, they made the assumption of low angles on the links to make cosx=1 but that is reasonably close for our rigs. Maybe I'll get the milliken book and look at it. So far MJ's drawing and my explanation agree but that doesn't mean it's right. Maybe close?
Figuring the derivation is probably not a topic for this post.

I'm a little concerned that two methods would be that far off. Scott's % is around 200% by the MJ/SW method but half that by the Gordon method? That sets my BS detector off. This is by no means a slam on Gordon, he seems to be one of the most knowledgable suspension types on the board and is willing to share some of it which is enormously useful. I just think if we want to look at this aspect of a suspension there needs to be some agreement on how to compare.

On a different note, I've run into the same pinion angle control problem with running a short upper link. I'd like to have a little upwards motion on the pinion as the suspension droops so I may end up a bit longer on the uppers.

Originally posted by mj


not too hard either
you can find the actuall CG, that means vertically as well as horizontally.
but that would be using a formula :rolleyes: wouldnt wanna try that

you wiegh the axles then raise one end to a set angle, then rewiegh the axles, plug numbers into formula and jus' like magic you have the CG

nothing wrong with formulas...as long as you're smart enough to not have to depend on them :) ...saves you the embarrasment of being suprised by the outcome...

I had a quote on my wall for a while that sums it up pretty good:
"All models are wrong, but some are useful."

Beartrack,

yes the pinion does point down a bit on droop and up on compression, but it is not too bad. Look at Lances cruiser or other rigs built by the snort guys. They figured that ratio out by trial and error, instead of from theory, but in the side view that suspension is pretty close to what I think would be optimal from the theoretical viewpoint. Lots of Arca contenders have similar setups too. It seems to work pretty good.

When I was in college a bunch of my buddies built four link rear suspensions as a senior project. The school had a truck scale and we used the method described to find the CG height. We were able to get the tires about 30 in of the ground. I weighed the front of my bronco level the rear level and both the front and rear with the opposite end elevated. So I had twice as much data as I needed to calculate the cg height. as it turned out the CG height was 6 inches different using one set of data compared to using the other set of data. Maybe that was a cheesey scale but that method did not work to well for me. I have used the same method on a race car using toledo scales and it did come out very repeatable but that car we were able to get up steeper than a 30 degree angle, and we had good scales.

why would they be the same?? with 3 inches of total wheel travel you may be able to (hypotheticly) design a system that optimizes a characteristic, let's say anti-squat, and ignore the negligable negative characteristic, let's say rear-steer...apply the same design with 30 inches of wheel travel and you're driving sideways anytime you flex...

road racers spend a lot more effort on removing/using roll steer then anyone in the 4x4 world does.
the theories apply the same but the compromises you have (or better yet are willing to) to live with to gain ground clearance change.

I believe I might have gained some insight this weekend into why "real life" seems to contradict the formula Stephen (etc.), namely why there seems to be far less antisquat in the rear than the formula seems to indicate.

Given our typical wheel base lengths and long front and rear link bars to accomodate the wheel travels we strive for, the link bar mounting points front and rear are often less than 2-3 feet apart. Thus a component amount of the antisquat from the rear is being negated by a component amount of the squat effect from the front; particularly because the front link frame-side/cross member side mounts for the front links are behind the front-to-rear center of gravity. Does any of this rambling of mine make sense or am I just envisioning this all wrong? My guess is that is why for example Walker Evans rig jacks so much in the rear; he has pretty short front link bars (and trailing front axle center linked as I recall.) So his front axle squat isn't negating his necessarily high antisquat in the rear... then again, I am just a newbie at all of this math compared to many up here.

Originally posted by Beartrack
Blah blah blah ... Thus a component amount of the antisquat from the rear is being negated by a component amount of the squat effect from the front; ...Blah blah blah

Yup.

If I am in 2wd mine will anti-squat very nicely, when it's in 4wd there isn't as much anti-squat (as in the entire vehicle lifting, the force is still there, which makes it great for climbing).

For those who haven't seen my setup, the front and rear link setups are identical (all 8 link bars are identical), except that the 2 front straight links are 2 inches more inboarded than the rear.

http://www.offroadsearch.com/antisquat1.jpg

Hi Toyman!

Yup, that's why last night I started building the front cross-member-side link bar tabs (for the outer front links) with 2 different holes for mounting points and the inner front link bar tabs with a single point inline with the lower holes of the outer bars. This should allow me to either focus all of the squat directly at the lower hole on the tabs (since all the link bars would be inline vertically, or to move the outer link bars up so that the vertical seperation points the link convergence point more towards the rear of the vehicle to more greatly negate the rear antisquat if it's too much. Hopefully it will work just fine with them mounted inline, but just in case it doesn't I have a little flexibility. I probably should have done the same for the rear too.

Toyman, you must have a ton of anti-squat! How far are your upper and lower links seperated vertically? 2" or 3"? Looks like maybe even less. I have 7" at the axle and 5" at the crossmember and it works good.

Originally posted by desertCJ
Toyman, you must have a ton of anti-squat! How far are your upper and lower links seperated vertically? 2" or 3"? Looks like maybe even less. I have 7" at the axle and 5" at the crossmember and it works good.

10" at the axle, 0 at the skid plate.

How good does that setup work for you?

Originally posted by desertCJ
How good does that setup work for you?

I don't think I could be any happier with it! It works great while crawling, climbing, and racing around the trails. It is a very predictable setup, it doesn't have any wierd characteristics. I can side hill like crazy, race around the trails at 50 mph, and do donuts. :)

Jason (SnortClown) from S&N Fab (http://www.sn-fab.com) basically designed the link setup and helped build it.

Ramps 1333 on a 20* ramp, and it still has travel left in the shocks, but I don't want to lighten the springs any just for ramp performance.

Cool, I want to wheel with some other people that have four links to compare them to mine. I'm pretty happy with mine but I haven't had the chance to compare with anyone else other than some TJs but those don't count:D They suck!

Originally posted by desertCJ
Toyman, you must have a ton of anti-squat! How far are your upper and lower links seperated vertically? 2" or 3"? Looks like maybe even less. I have 7" at the axle and 5" at the crossmember and it works good. your link system is one of the most correct i have seen . the spred is good its almost the 80% formula i bet that thing hooks.7'' at axle 7x80%=5.6'' at the frame you are on the mony thats is how you do it.:)

Hello again, Frankie! So, on my Sidekick, the link spread on my front axle is 6.5 inches, and only 2.00" at the frame. The lower link is at 15 degrees, and the upper is at 10 degrees. Would I be smarter raising the mount of the upper, or dropping the lower? I am limited in my room for the upper wishbone, but have heard people mumbling stuff about pointing links at the CG. What's that about?

Thanks Frankie, my Jeep does climb pretty good and I don't notice it jacking the rear end up at all even when I hammer it...I"m just wishing for a little more wheelbase. I'm at 96" right now and I'd like about 100" I think. Maybe even a little more.:skull:

Originally posted by twistedmetal
Hello again, Frankie! So, on my Sidekick, the link spread on my front axle is 6.5 inches, and only 2.00" at the frame. The lower link is at 15 degrees, and the upper is at 10 degrees. Would I be smarter raising the mount of the upper, or dropping the lower? I am limited in my room for the upper wishbone, but have heard people mumbling stuff about pointing links at the CG. What's that about? i do not know what the center of gravity is about maybe its where the truck frame will ballance at?on the front links its not as important as the rear but i use the same formula front and rear if i can. the set up you have will work ok.and it will keep your shaft pointing at the tcase yoke all the time but it will loose caster during the suspension cycle.so what your not desert racing are you?

Originally posted by Toyman


I don't think I could be any happier with it! It works great while crawling, climbing, and racing around the trails. It is a very predictable setup, it doesn't have any wierd characteristics. I can side hill like crazy, race around the trails at 50 mph, and do donuts. :)

Jason (SnortClown) from S&N Fab (http://www.sn-fab.com) basically designed the link setup and helped build it.

Ramps 1333 on a 20* ramp, and it still has travel left in the shocks, but I don't want to lighten the springs any just for ramp performance.

I rode for one very fun day in this buggy and all I can say is wow. We scaled an impressive wall at Reiter (near Goldbar, WA) maybe 35 feet or so high (locals probably know the one I am talking about) and then blasted down the lumber roads at 45 mph - including taking a hard turn that was reverse graded/burmed with a hole from a dried up puddle in the middle of it. I don't white knuckle easily but I realized after coming out the other side of the turn that I was still waiting for the body to severely roll (and maybe even roll the whole rig) and that thing hadn't even STARTED to body roll yet and the corner was just about behind us! If mine is even remotely close to Mikes in performance I will be happy as can be. Mike's rig iis stable as can be yet still articulates like crazy and sticks like glue. Best rig I've ever ridden in. Check out the sheer lack of body roll on the S&N Fab (http://www.sn-fab.com) home page (Mike/Toyman's rig is the blue buggy.)