need help with 3-link #'s

I'd ask over at pirate but figured I'd get better responce here. I'm building a 3-link on the cherokee and have been working with the calculator. After hours of hair pulling I've got some decent numbers( I think) Can someone with some experiance/knowledge help me out.

Here's what I got

Anti squat 29.11
Role axis 6.53
Role center height 13.92


Now these other 2 numbers I have no Idea what they are so good or bad can someone explain

instant center x 1683
instant center z 176

Thanks for any help you can give
Robert

I wouldn't worry to much about the numbers up front. Being a steering axle you a usually control most of the effect of things like roll axis.

That said, your roll axis is a little high. Can you spread out the lowers (horizontally) on the axle or bring them in on the frame side, that will help out there.

Your instant X seems high likely because your links are almost parallel to each other. The anti-squat might be a bit low, but that is going to depend on your intended usage for your XJ.

Again, the numbers up front don't really matter a whole heck of a lot. Get some good separation (vertically) both on the axle and frame side, make sure they clear everything and you should be pretty much set. Build some adjustability into the upper link so you can play around with different instant centers and anti-squats once you get it driving.

For me, my anti-squat is ~64% with a 2 degree roll axis. I've found that to work for out east coast stuff. I also can dial that back to ~82% anti-squat (obviously with a lower instant center) but I have not felt the need.

Not sure how much more I can spread the lowers. Here are the rest of my numbers to help see where I am

Upper
frame 33- 11-26
axle 0 - 11- 23


lower
frame 34.5- 11.75 -19
axle 3- 18 -16


I'm not sure where to massage numbers to help. Give me the material and I can build it but figure out the design i'm lost.

This is on a waggy front axle. Not real sure what other info I can give to help

Well without knowing how you are building it it is hard to give link placement suggestions. I do not see a reason why the lower frame side can't come in further. 1/2 your separation now is 11.75", try dropping that to and see what happens.

Your panhard will also have an effect on roll axis and also keep in mind these numbers are only for ride height and change throughout travel. Again, worry more about the numbers in the rear on a none steering axle.

OK, so there are the numbers, who can interpret what they mean?

No such thing as anti-squat on a front axle, roll axis angle is meaningless since you're steering the thing. Put the lowers where they fit, and make the upper as close to level as possible, and you will have a good working 3 link.

If it's mid arm, mount the lowers below the frame for a more level arm position, if it's long arm mount the lowers inside the frame for better ground clearance, mount the lowers even with the axle tube both for ground clearance and for a more level arm. Mount the upper where it is close to level. No rubber bushings in the upper arm, and not recommended in the lowers. Roll center height is totally controlled by the panhard bar height, so make it as tall as you can. Set the chassis on the bump stops (collapsed position) and see how high you can position the panhard bar, going higher on the frame helps. There you go.

You can play with the calculator, but no one can tell you how the different numbers will perform in the front.

Goatman said:

No such thing as anti-squat on a front axle, roll axis angle is meaningless since you're steering the thing.

Click to expand...

Ok, so it is really anti-dive up front. Close enough, no need to add another word to further confuse the guy. Roll axis is combat-able with a steering axle, but isn't something to just "forget about".

Goatman said:

Put the lowers where they fit, and make the upper as close to level as possible, and you will have a good working 3 link.

Click to expand...

Just a little more complicated than that.
Like I mentioned above several time, numbers aren't the end all for the front, but you can't just throw links places and expect it to function correct. There are a few basics to consider (some of which I mentioned above and you cover below).

Goatman said:

If it's mid arm, mount the lowers below the frame for a more level arm position, if it's long arm mount the lowers inside the frame for better ground clearance, mount the lowers even with the axle tube both for ground clearance and for a more level arm. Mount the upper where it is close to level. No rubber bushings in the upper arm, and not recommended in the lowers. Roll center height is totally controlled by the panhard bar height, so make it as tall as you can. Set the chassis on the bump stops (collapsed position) and see how high you can position the panhard bar, going higher on the frame helps. There you go.

Click to expand...

Pretty much spot on. To the OP, Goatman knows his stuff (probably moreso than I), I think he may have just oversimplified the top portion of this post.

Goatman said:

You can play with the calculator, but no one can tell you how the different numbers will perform in the front.

Click to expand...

i tried to get good numbers so i could have bragging rights on the internets.

ktm racer 419 said:

i tried to get good numbers so i could have bragging rights on the internets.

Click to expand...

I look at it like trying to get a high score, the bigger the numbers the better.

:thumbup:

RCman said:

Ok, so it is really anti-dive up front. Close enough, no need to add another word to further confuse the guy. Roll axis is combat-able with a steering axle, but isn't something to just "forget about".
Just a little more complicated than that.
Like I mentioned above several time, numbers aren't the end all for the front, but you can't just throw links places and expect it to function correct. There are a few basics to consider (some of which I mentioned above and you cover below).

Pretty much spot on. To the OP, Goatman knows his stuff (probably moreso than I), I think he may have just oversimplified the top portion of this post.

Click to expand...

OK, so explain how the different numbers effect performance. Why is a particular number going to perform better than another number? Anti-dive is the opposite of anti-squat, so which number is a good number, and what will each number do?

No, it's really that simple.

So basically the more I read the more I screwed myself. I was thinking the numbers on the front axle were the same as a rear, bad #'s ment bad handling. And I had no Idea the panhard bar affected role center height, I hadn't even messed with numbers from that.(left the preinputted numbers from the calculator)

I appreciate all the input, should have asked earlier. Makes alot more sense now

Goatman said:

OK, so explain how the different numbers effect performance. Why is a particular number going to perform better than another number? Anti-dive is the opposite of anti-squat, so which number is a good number, and what will each number do?

No, it's really that simple.

Click to expand...

These discussions could last 5 pages and we'd end up in the same place.
Like I've said since the 1st post, numbers are not the end all.

Simple, sure. But it is a little more involved then "put the the lowers were they fit and make the upper level".

You've built more than me and I can't tell you first hand what all the different numbers will do. I can tell you the my XJ drives "better" with my UCA in one slot over the other (and I built it with this in mind that I'd want to try different combos). I can say what they theoretically do, but I'm surly not going to build a bunch of them to test them out. A really low percentage of anti-dive will try to drive the chassis under the axle (just like a high percentage will try and make the chassis go over the axle, go ahead and draw the links out exaggerated and this becomes clear). Your plan of keeping the links flat does combat this naturally. I'm not arguing what you have said is incorrect. I'm simply saying that there are things to look at when placing links in their locations and to make sure those forces are going the way that would make the most sense.

All I was trying to get to was to expand on your second statement of "Put the lowers where they fit, and make the upper as close to level as possible, and you will have a good working 3 link" really should add decent separation at the axle and frame sides is more important than the flat/level upper. Obviously you don't want large angles from horizontal, but sometimes a flat/level upper can cause negative effects if you just place the lowers where they fit. Just as in my case, my anti-dive would jump through the roof and probably make in much less drivable.

Follow that last paragraph and you'll never even have to look at the numbers or care what they do as they'll fall right "into place".

Of course, the paragraph below the one of mine you've quoted clarifies what I was saying, and is all the info someone would need to build a good working 3 link on an XJ. I can't argue with you that there is a right way to do it, yes there is, I just challenge you or anyone else to explain exactly what the numbers mean.......which you haven't done yet. Please understand this is all in fun, I'm not really challenging you or anyone else to anything. We can say that the numbers are meaningless, which they really aren't (like you're saying), but they're as good as meaningless because no one can explain how the different numbers will perform (like I am saying).

I sort of understood that someone doing this would understand that there needs to be sufficient link separation, but again, there's no way to get this from the numbers.

A high roll center is desired on a trail rig, but the height of the roll center (which is the panhard bar) is totally dependent on the lift height and the frame and pan clearance, so the calculator numbers mean nothing. Roll axis angle really does mean nothing when you can steer. Anti-squat is the opposite in the front than it is in the back because the tires are turning in the opposite direction relative to the links, and it's the direction and force of torque acting on the links that produces anti-squat. Traction and bouncing under power are issues in the rear, and affected by anti-squat percentage, but the front is different. So, again, the calculator numbers don't give useful information. Of course, a trained suspension engineer could tell us something, but I've yet to see anyone on a 4x4 forum that can do it.

Please excuse me continuing this dialogue, while it probably looks like I'm trying to prove myself right, so to peak, my interest really lies in simply furthering a discussion with info that might be helpful to whoever else might read it. :cheers:

The two of you can keep going as long as you want. The more you guys stress on why/how something works the more people will start to understand.(me included) I understand 10x more in 2 days than I did reading 3 link info on pirate for the past week or 2.

So thanks again

rkates said:

The two of you can keep going as long as you want. The more you guys stress on why/how something works the more people will start to understand.(me included) I understand 10x more in 2 days than I did reading 3 link info on pirate for the past week or 2.

So thanks again

Click to expand...

X2
Keep it up, I'm learning alot.