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post #1 of 28 Old 02-18-2008, 03:51 AM Thread Starter
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body roll on a budget boost

Hey, guys. I installed a Black Diamond b/b on my Rubi Unlimited. reused the stock shocks... with Poly shock mounts out back. The JK rides kinda smooth anyway, but this thing has ALOT of body roll now. still stock links on the swaybars... while not a geometry major, I don't think that has much to do with how much it rolls.

Yes, I know I'm raising the center of gravity and all, but this alot of roll. My ZJ is on 5.5" and Long Arms... and it rolls like the JK does... but it currently doesnt have a front swaybar.

Just seems odd for this rig.
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post #2 of 28 Old 02-18-2008, 08:16 AM
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Originally Posted by b1pig View Post
still stock links on the swaybars... while not a geometry major, I don't think that has much to do with how much it rolls.
The more the sway bar ends move away from horizontal the less effective the sway bar will be.

You've changed the roll center as well as the CoG, and that will have an impact on body roll.
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post #3 of 28 Old 02-18-2008, 11:59 AM
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The more the sway bar ends move away from horizontal the less effective the sway bar will be.

You've changed the roll center as well as the CoG, and that will have an impact on body roll.
Actually, I think it's the other way around. When the sway bar is horizontal, the links act on it through the "longest lever arm". As the sway bar ends move lower (or higher), the effective lever arm presented to the links is shorter and the bar effectively becomes stiffer. (As an extreme example, if the sway bar ends were rotated such that they lined up exactly with the links, the links wouldn't be able to twist the bar at all and it would effectively become completely ridgid.)

I wonder if the problem could be that the electronic sway bar isn't actually connecting in this case, maybe because things aren't lining up correctly after the lift. It would be interesting to try disconnecting one of the links and see if the bar is actually connected.
post #4 of 28 Old 02-18-2008, 12:03 PM
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Actually, I think it's the other way around. When the sway bar is horizontal, the links act on it through the "longest lever arm". As the sway bar ends move lower (or higher), the effective lever arm presented to the links is shorter and the bar effectively becomes stiffer.
You may be right about stiffness, at least when shortening the links, but I've always understood that proper sway geometry called for the ends to be parallel to the road, and the more that you move away from that, the less effective the sway bar becomes.
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post #5 of 28 Old 02-18-2008, 12:09 PM
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Originally Posted by gcg View Post
I wonder if the problem could be that the electronic sway bar isn't actually connecting in this case, maybe because things aren't lining up correctly after the lift. It would be interesting to try disconnecting one of the links and see if the bar is actually connected.
You'd think the light would be flashing? It is definitely worth disconnecting one end to find out for sure.
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post #6 of 28 Old 02-18-2008, 12:18 PM
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This explains it better than I can:

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As you can see in the sketch below, on the left hand side is a sway bar set up with the ends parallel to the ground (the dotted bar outline in the center shows the rest position). Under cornering load, the bar is twisted up by the suspension loads, F1 is the force of the outside side being compressed upward, F2 is the force of the inside side pulling the sway bar downwards. If the bar starts out horizontal and then the two effective bar end lengths (L1 and L2) are equal, since one end is twisted upward to the same angle as the other end is twisted downward. On the right had side is an illustration of what happens if the sway bar does not start out horizontal. This would be the case if a suspension lift were installed (thus raising the frame and the sway bar attached to it) without extending the end links. In this example, you can see that as the one end of the bar twists upward, it's effective length, L1, gets longer and longer as the angle is decreased towards horizontal. And the effective length of the end of the bar twisting down, L2, gets shorter as it's angle increases. Since the torque in the bar must necessarily be balanced, F1*L1 must equal F2*L2. Since L2 is less than L1, F2 must be higher than F1 to maintain the equality of the torque in the bar. This means that there is less force supplied by the sway bar to the outside suspension component in the turn so the vehicle will lean farther than it would if the forces and lengths were equal, as they are on the left side of the sketch. Thus if the purpose of a sway (or anti-roll) bar is to resist body roll, then the most efficient setup is to have the ends of the sway bar as close to parallel to the ground at rest as possible.
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post #7 of 28 Old 02-18-2008, 05:03 PM
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Good explanation makes sense.

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post #8 of 28 Old 02-18-2008, 09:53 PM
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This explains it better than I can:
That's an interesting explanation!

I think there are two things at work here. One factor is the apparent shortening of the sway bar ends (for example, L1 vs. L2 in your diagram). If you look at adjustable sway bars, one of the most popular techniques is simply to allow the attachment point of the link (to the sway bar end) to be adjustable (they can be adjusted back and forth on the ends, essentially shortening or lengthening the "lever arm"). If they are adjusted in a direction that lengthens the distance between the link and the bar, the sway bar becomes soft. If they are adjusted closer to the bar, the bar is stiffened (because of the shorter lever arm). In effect, this is the same thing that happens when the bar runs off horizontal. The "effective" length of the "end" is shortened and hence the "effective" lever arm is shortened.

The other factor (which I hadn't considered) is the asymetry in the effective lengths of the lever arms that is introduced when the bar runs off the horizontal position - as you pointed out nicely in your diagram.

I believe that both of these have an effect and I guess it would depend on the relative magnitude of each to see how the overall roll stiffness would be changed by running the bar off horizontal.

One thing to consider is that the amount of body roll is generally fairly small, a few degrees, so the two sway bar ends aren't going to be splayed that far apart under normal cornering loads. In that case, L1 and L2 won't be hugely different from eachother so I'm not sure how significant the difference introduced by this factor will be.

I'm also not convinced that the statement that "the force on the outside is reduced" is the important factor here. The sway bar reduces body roll by introducing a torque along the roll axis that counters the torque that is making the body want to roll. If you look along the long centerline of the vehicle, this counter torque is produced by F1 and F2 acting on the attachment points of the sway bar, one up and the other down. If we call the distance from the roll center to the attachment points "d", then the (counter) torque would be something like (F1 + F2)*d, so it's (F1 + F2) that's important, not just the force on the outside. If one force increases and the other decreases, the counter torque could remain the same.

All interesting food for thought!
post #9 of 28 Old 02-21-2008, 12:39 AM Thread Starter
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That's an interesting explanation!

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post #10 of 28 Old 02-21-2008, 09:19 AM
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Huh?
post #11 of 28 Old 02-21-2008, 11:05 PM Thread Starter
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sorry... i tried a BB funny....

i click quote, and it shows greek.

είμαι ταραγμένος

---------------------

so, the theory is that the length of the swaybar links are playing a big part in this?

i get the idea of raising the center of gravity.... technically, the roll center has changed very little, half of the total lift, again, by theory, right? The amount of roll is extremely surprising. the swaybar is connected.

i didnt mention it in the intial post, but the engine torque is also more pronounced as well when accelerating hard. the Jeep twists a lot more than it did... which to be honest... it didnt twist at all unless the swaybar was disco'd.
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post #12 of 28 Old 02-22-2008, 10:20 AM
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Quote:
Originally Posted by b1pig View Post
so, the theory is that the length of the swaybar links are playing a big part in this?
Maybe, maybe they are just one contributory factor. It certainly can't hurt by getting them set right.


Quote:
i get the idea of raising the center of gravity.... technically, the roll center has changed very little, half of the total lift, again, by theory, right? The amount of roll is extremely surprising. the swaybar is connected.
Higher CoG and higher roll center, will obviously have an influence on body roll. Did you use track bar relocation brackets?


Quote:
i didnt mention it in the intial post, but the engine torque is also more pronounced as well when accelerating hard. the Jeep twists a lot more than it did... which to be honest... it didnt twist at all unless the swaybar was disco'd.
What do you mean by twist? The body twists or the steering twists? If the rear and front tracks are out of line, then it can force the vehicle to drive funny and it kind of feels like torque steer.


Finally, and I know this is obvious and you already know it, but it's worth repeating, don't forget it's a Jeep, not a sports car, or even an SUV, it will not handle like either.

That said, mine handles and rides just fine and I don't have any body roll issues.
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post #13 of 28 Old 02-22-2008, 11:11 AM
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Originally Posted by b1pig View Post
sorry... i tried a BB funny....

i click quote, and it shows greek.

είμαι ταραγμένος

---------------------

so, the theory is that the length of the swaybar links are playing a big part in this?

i get the idea of raising the center of gravity.... technically, the roll center has changed very little, half of the total lift, again, by theory, right? The amount of roll is extremely surprising. the swaybar is connected.

i didnt mention it in the intial post, but the engine torque is also more pronounced as well when accelerating hard. the Jeep twists a lot more than it did... which to be honest... it didnt twist at all unless the swaybar was disco'd.
I think the role that is being played by the sway bar links is that they are forcing the sway bar ends to "hang down" such that they are not horizontal anymore and that changes the geometry between the link and the sway bar. It appears that there are several effects due to this changed geometry, as have been mentioned, and it's not real clear which of these effects are the most important. But it does seem that they can change the effectiveness of the sway bar.

As PhilD mentioned, changing to longer links so that the sway bar ends are horizontal would be a really good thing to try and would most likely fix your problems.

Just as an aside, my electronic sway bar disconnect failed in the "disconnected state" a while ago. I ended up driving the Jeep for a while in this condition until I could get it fixed. I noticed quite a bit of body roll, too, and found it quite concerning. When the sway bar is connected, though, I find very little body roll (as PhilD also mentioned), so you should be able to cure the problems you are experiencing once the geometry is right.

I'm sure you've already checked this, but it is important that all the link attachment points and the sway bar attachment points are tight.
post #14 of 28 Old 02-22-2008, 11:32 AM
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Originally Posted by gcg View Post
Just as an aside, my electronic sway bar disconnect failed in the "disconnected state" a while ago. I ended up driving the Jeep for a while in this condition until I could get it fixed. I noticed quite a bit of body roll, too, and found it quite concerning.
I lost a bolt out of sway bar link (after a field repair of one) and immediately noticed a difference, even on the highway. I definitely would not want to drive around like that.
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post #15 of 28 Old 02-22-2008, 05:10 PM Thread Starter
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what i mean by "twist" is the torque effect... when you accellerate in a straight line, the Jeep leans to the right. ever watch a drag car at the strip? extreme example... but thats what I mean.
the only change i made was the addion of the spacer kit and the P.P. rear shock brackets.

youre not insulting my intellegence or anything. i understand the general concept.... when you start the a2>b2 +(y3-z)=leverage ... i quit reading. thinking hurts for those not accustomed to it.

this is my other Jeep:


i realize every Jeep often reacts differently to a lift or a modification, it just seemed such a drastic change. I lifted my ZJ with a 2" b/b... then used 3.5" coils and later used the coils and b/b together.... and like i said... it never handled like that with the swaybars connected.
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post #16 of 28 Old 02-22-2008, 05:40 PM
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I lifted my WJ with 2" coil spring spacers and no sway bar extenders and I thought the body roll decreased. It rides a bit firmer in any case, and I've always liked it that way.
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post #17 of 28 Old 02-22-2008, 10:07 PM
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what i mean by "twist" is the torque effect... when you accellerate in a straight line, the Jeep leans to the right. ever watch a drag car at the strip? extreme example... but thats what I mean.
the only change i made was the addion of the spacer kit and the P.P. rear shock brackets.

youre not insulting my intellegence or anything. i understand the general concept.... when you start the a2>b2 +(y3-z)=leverage ... i quit reading. thinking hurts for those not accustomed to it.

this is my other Jeep:


i realize every Jeep often reacts differently to a lift or a modification, it just seemed such a drastic change. I lifted my ZJ with a 2" b/b... then used 3.5" coils and later used the coils and b/b together.... and like i said... it never handled like that with the swaybars connected.
Very cool picture of your ZJ!

Your situation is really puzzling. I definitely don't think you should be seeing any substantial increase in body roll based on the mods you made. Yet it sounds like the change you are experiencing is extreme.

How far off horizontal is your sway bar? Could you post a quick picture of it from the side so we can see what angle it is running at?

Are you absolutely certain that the electronic disconnect unit is "connected"? You could determine this by disconnecting one of your links (and leave the other one connected) and then seeing whether you can move the disconnected side of the sway bar up and down or not.
post #18 of 28 Old 02-23-2008, 02:17 AM Thread Starter
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when i read your post yesterday, it got me thinking about the swaybar. the light is out, so it should be connected. when i did the install, the swaybar was connected. I'm also wondering if there is something that keeps the collar from sliding over if the swaybar is at/beyond a certain angle.

I'll snap a pic when I get home from work this morning... so long as i dont fall into a sleep-hazed stupor in the driveway. sleep is a commodity i havent had a lot of lately.
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post #19 of 28 Old 02-23-2008, 06:22 AM
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I'm also wondering if there is something that keeps the collar from sliding over if the swaybar is at/beyond a certain angle.
No it will connect at any angle as long as both ends are lined up. As GCG keeps saying though, it is important that you verify it is actually working and connected.
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post #20 of 28 Old 02-23-2008, 06:25 AM
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Your situation is really puzzling. I definitely don't think you should be seeing any substantial increase in body roll based on the mods you made. Yet it sounds like the change you are experiencing is extreme.
X2 It sounds like either the sway bar disco is not working, or something is loose. Have you checked the torque on all the control arms, track bars, etc. Is the rear sway bar connected?
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post #21 of 28 Old 02-23-2008, 06:52 PM Thread Starter
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welp.
its readily apparent that the swaybar is not connected. which is a big WTF, over! I didnt even bother removing the bolts... i just opted to drive around the corner.

this is with the swaybar "connected"


i still need longer links



i've lifted the tires a few times with the swaybar connected.


in the end i feel like a total idiot.... but the fact is i rarely get to drive it.

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post #22 of 28 Old 02-23-2008, 08:34 PM
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It does look as if the sway bar is in the "disconnected" state. But it's hard to tell for sure from the angle of the picture. I think it would still be worthwhile to pull a bolt on one of the links and verify that you can move that end of the bar up and down when the other link is still connected. Then you'll know for sure that it is disconnected even though the light is off.

For what it's worth, when my electronic disconnect first failed the light was blinking continuously indicating that it was trying to connect but couldn't. After the dealership played with it for awhile, the light went out completely but the sway bar was still disconnected. It's possible you have something similar going on.

If the electronic disconnect is bad, it's expensive if you have to replace it yourself (I think the dealer told me it was a $1500 part). The dealership I went to was really excellent and they worked hard to get it covered under warranty, for which I was very thankful. Apparently the disconnect unit and swaybar are considered a "single sealed unit" and they can't open or repair the disconnect unit or separate it from the sway bar itself - they just replace the whole thing.
post #23 of 28 Old 02-24-2008, 10:42 AM Thread Starter
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no doubt its disco'd. it would have lifted a tire. i've ran that thing several times offroad.... and i've used that disco alot.

this is the first issue i've had out of mine, though. i cycled it last night and there is no difference between dico'd and connected. when i got the reflash for the stall-bug, they didnt follow all the directions because my swaybar light went to flashing.... but it worked normally. i'm sure my dealer will replace it, but the timing is extremely odd.
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post #24 of 28 Old 02-24-2008, 11:08 AM
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its readily apparent that the swaybar is not connected.
Which is what GCG said in his first post on this thread, good diagnosis GCG
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post #25 of 28 Old 02-24-2008, 12:10 PM
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Which is what GCG said in his first post on this thread, good diagnosis GCG
Thanks! It's been an interesting thread and I always enjoy learning new stuff from the discussion. Your points regarding running the sway bar off of horizontal were interesting and enlightening.
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