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Unread 01-02-2012, 09:07 PM   #61
Climbit
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Quote:
Originally Posted by fratis View Post
i think we agree but are referring to two different worlds. i know perfectly well what bumpsteer is and why it happens. the inherent bumpsteer that would be experienced with a 4link and draglink steering i dont think would be that bad if the angles were conservative and we are discussing a primarily offroad vehicle. yes you eliminate a whole lot of issues with full hydro steering this is obvious and more and more are going this route. before that became so popular, however, there were a lot of 4 links with draglink steering. at some point any offroad vehicle with a drag link is going to experience some version of bumpsteer no matter how parallel of even the two units are. agreed not within normal operational range such as experienced on the road it would take a bit of articulation. i have yet to see a panhard frame side mounted directly behind the pitman arm and the axle end mounted as far out as the steering on the knuckle. there are always compromises to be made. getting a panhard and drag link parallel and with similar angles is relatively simple with a lift kit, off the shelf parts, and factory or near factory axle assemblies. doing so with a one-off is again a different world. im reworking mine now and it is a challenge.

its not necessarily the theories im disagreeing with but rather the physical building of what is being discussed.
here is the setup I am running. In order to get them both perfectly parallel I had to set it up as inverted T. however after talking to some experts I have decided I am not going to live with the dead spot and wandering of that geometry and go back to a Y link. it's going to require some work but It will be worth it IMO


the panhard does not need to be mounted directly behind the pitman arm, and it should not come out as far as the steering knuckle.

as long as they are parallel in both directions and the same length, the arc of travel will be the same.

you may think that having some bumpsteer on a trail rig is acceptable, but I think if you ran a few miles at speed through the whoops to get between trails you would be singing a different tune.


I won't argue that it is hard to do, but it is possible.

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Unread 01-03-2012, 11:34 AM   #62
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not pushing this for argument sake but rather in the spirit of debate. if a 4link and draglink combo would produce unacceptable amounts of bumpsteer how can we then compare that to a leafsrung vehicle with a draglink? with leaves, theoretically the axle droop would be straight down with a bit of rearward shift as a 4 link would create. ive had a leaf front with horrid bumpsteer and one without. im sure when put in high articulating moments my steering was being pulled a bit to one side (what i was alluding to in a previous post) but with so much other things going on and the slow rate of speed it wasnt really noticeable. i also didnt have any noticeable bumpsteer on higher speed sections where the suspension was cycling only a few inches in either direction.

not a real fan of the inverted y or t setup. for those of us with draglinks and tierods both attaching all the way over on the hi steer arm, getting even and parallel is a bit trickier. this is aggravated when building a slightly lower setup. if i were to make the panhard as long as the draglink it would be into the coil-overs or unacceptably close.

if you did in fact convert from the inverted "t" to an inverted "y" would you then need to make the panhard as long as the new draglink or simply to the point at which your tierod attaches to the draglink? seems like you would need a longer panhard. looks like that would be tricky to do in your case as well. would it not be easier to add assist to see if that didnt smooth out the flat spot rather then redoing everything?
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Unread 01-03-2012, 12:50 PM   #63
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Equal length does not yield concentric arcs without their pivot points in line front to back. Neither does parallel if their pivot points are not in line.

If the links don't travel in concentric arcs, then there is bump steer at some point in the range of motion. How large that range of motion is depends on a lot of variables.

A shorter track bar that is in a slightly lower plane and a slightly flatter angle, in relation to the drag link, can actually create a quite acceptable range of motion without perceptible bump steer.

Equal length certainly makes creating a large "sweet spot" easy, but it is not all that easy to implement.

Then the other dirty secret nobody ever talks about with regard to steering. The track bar is a suspension component and not a steering component.

The track bar sets your roll center characteristics (stiffness and height) and also can cause asymmetrical handling (oversteer and understeer) which is also similar to bump steer in that it causes steering input that didn't come from the steering wheel.

OEM trucks don't have equal length, and also don't have perceptible bump steer. And if you looked at their cad design specs, you would see they are not parallel either.
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Unread 01-03-2012, 05:10 PM   #64
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Quote:
Originally Posted by fratis View Post
not pushing this for argument sake but rather in the spirit of debate. if a 4link and draglink combo would produce unacceptable amounts of bumpsteer how can we then compare that to a leafsrung vehicle with a draglink?
with a leafsprung vehicle, ideally you get the drag link as long and as flat as possible at right height, thus minimizing any potential bump-steer, but it will happen. the only way to truly eliminate it is to run a panhard that is equal length and paralell.

Quote:
with leaves, theoretically the axle droop would be straight down with a bit of rearward shift as a 4 link would create. ive had a leaf front with horrid bumpsteer and one without. im sure when put in high articulating moments my steering was being pulled a bit to one side (what i was alluding to in a previous post) but with so much other things going on and the slow rate of speed it wasnt really noticeable.
right at low speed a considerable amount of bumpsteer can be liveable.

Quote:
i also didnt have any noticeable bumpsteer on higher speed sections where the suspension was cycling only a few inches in either direction.
it all depends on the setup. I know a couple people who have had minor bumpsteer and lived with it almost unnoticed on slow trails, but the first time they took it at high speed across the desert they noticed it. I was one of those people.

Quote:
not a real fan of the inverted y or t setup. for those of us with draglinks and tierods both attaching all the way over on the hi steer arm, getting even and parallel is a bit trickier. this is aggravated when building a slightly lower setup. if i were to make the panhard as long as the draglink it would be into the coil-overs or unacceptably close.
I have toyed with it, and the only way to get the drag link to the knuckle is to cut the coil buckets off and move them back. something I am not going to bother while keeping the D30. when the time comes and I go to 1-tons I will start with bare tubes and completely re-do everything. but until then inverted Y should suffice.

Quote:
f you did in fact convert from the inverted "t" to an inverted "y" would you then need to make the panhard as long as the new draglink or simply to the point at which your tierod attaches to the draglink?
no, the panhard will be re-built to the length of the drag link (pitman arm to knuckle)

Quote:
looks like that would be tricky to do in your case as well.
it will probably end up back near the stock location I am going to have to fab a mount of course since the stock one is mostly gone, but it will be doable.

Quote:
would it not be easier to add assist to see if that didnt smooth out the flat spot rather then redoing everything?
potentially. however I am not willing to sink the time and money into assist, and then mounting it for this setup, only to find out that it does not solve my problems. then I am going to have more things to deal with when re-doing the geometry. assist will be added once I have the steering dialed in without it.

Quote:
Originally Posted by ftgiles View Post
Equal length does not yield concentric arcs without their pivot points in line front to back. Neither does parallel if their pivot points are not in line.
equal length and parallel creates concentric arcs to a point. then of course the arcs would intersect unless the pivot points were both in the same plane.

however when you are talking about an offroad suspension that can really only travel 16-20" MAX there is no way you would run into that problem. that would require several feet of travel.

Quote:
If the links don't travel in concentric arcs, then there is bump steer at some point in the range of motion. How large that range of motion is depends on a lot of variables.
the variables being panhard/drag link length and suspension travel. as long as your panhard and drag link

Quote:
A shorter track bar that is in a slightly lower plane and a slightly flatter angle, in relation to the drag link, can actually create a quite acceptable range of motion without perceptible bump steer.
right and the longer the links, the larger the "acceptable range"

Quote:
Equal length certainly makes creating a large "sweet spot" easy, but it is not all that easy to implement.
true. hence why I ended up with inverted T

Quote:
Then the other dirty secret nobody ever talks about with regard to steering. The track bar is a suspension component and not a steering component.
it is certainly mostly a suspension component; however it does also play a large role in steering as well.

Quote:
The track bar sets your roll center characteristics (stiffness and height) and also can cause asymmetrical handling (oversteer and understeer) which is also similar to bump steer in that it causes steering input that didn't come from the steering wheel.
correct,this is a good reason why it should be as long and as flat as possible to minimize the amount that it pulls the axle to one side or pushes it to the other through suspension travel.

Quote:
OEM trucks don't have equal length, and also don't have perceptible bump steer. And if you looked at their cad design specs, you would see they are not parallel either.
right, but OEM vehicles do not have the same kind of travel that we are talking about in an offroad suspension. however OEM TJ/XJ are both parallel and the same length (+/- .5" for steering wheel centering)
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Unread 01-03-2012, 06:27 PM   #65
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Originally Posted by Climbit View Post


correct,this is a good reason why it should be as long and as flat as possible to minimize the amount that it pulls the axle to one side or pushes it to the other through suspension travel.
Long and flat have nothing to do with the roll center characteristics defined by the track bar.

The roll center is set by the center point of the track bar mounting locations. The roll center height is determined by how high that roll center location is from the ground. The front roll center and the front roll center height both need to be in sync with the rear roll center and roll center height.

"as long and as flat as possible" and only paying attention to its relationship with the draglink will definitely get you wierd behavior problems at higher speeds. Typically the front roll center height should be lower than the rear and if the rear roll center is off center the the front should be complementary to the rear.


Quote:
right, but OEM vehicles do not have the same kind of travel that we are talking about in an offroad suspension. however OEM TJ/XJ are both parallel and the same length (+/- .5" for steering wheel centering)
So the conversation stays reasonable, the TJ/XJ track bar is 31.5" and the drag link is 37".
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Unread 01-03-2012, 06:37 PM   #66
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Originally Posted by ftgiles View Post
Long and flat have nothing to do with the roll center characteristics defined by the track bar.

The roll center is set by the center point of the track bar mounting locations. The roll center height is determined by how high that roll center location is from the ground. The front roll center and the front roll center height both need to be in sync with the rear roll center and roll center height.

"as long and as flat as possible" and only paying attention to its relationship with the draglink will definitely get you wierd behavior problems at higher speeds. Typically the front roll center height should be lower than the rear and if the rear roll center is off center the the front should be complimentry to the rear.
you are correct, but having it as long and flat as possible minimizes the amount that it moves the axle side-side which can cause unwanted steering input at speed.


Quote:

So the conversation stays reasonable, the TJ/XJ track bar is 31.5" and the drag link is 37".
odd, before I went inverted T, my track bar was ~34" and my drag link was within .5" of it. my steering wheel was center and the axle was center at ride height, which was about 1" higher than center of travel.

I haven't measured a stock jeep, but I didn't think they would be that far off.
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Unread 01-03-2012, 07:16 PM   #67
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Originally Posted by Climbit View Post
you are correct, but having it as long and flat as possible minimizes the amount that it moves the axle side-side which can cause unwanted steering input at speed.
I'm all for limiting the side-to-side movement of the axle by having a flatter track bar, but it's way down the list of priorities and you'll probably never get that far down in the list, so it will be what ever it is.

As far as causing steering input... Not if the drag link/track bar relationship is correct. Flatter definitely gives you a larger "sweet spot" for sure!


Quote:
odd, before I went inverted T, my track bar was ~34" and my drag link was within .5" of it. my steering wheel was center and the axle was center at ride height, which was about 1" higher than center of travel.

I haven't measured a stock jeep, but I didn't think they would be that far off.

From a 2001 XJ

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Unread 01-03-2012, 07:43 PM   #68
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Originally Posted by Climbit View Post

but OEM vehicles do not have the same kind of travel that we are talking about in an offroad suspension. however OEM TJ/XJ are both parallel and the same length (+/- .5" for steering wheel centering)
So the point I'm trying to make is same length and parallel is an ideal. And you can have very acceptable steering without extending the track bar out past the springs.

Blaine has created a cult-like following with his steering setups. And they are fine, indeed. But that very same cult will also tell you how great their Currie HD steering is with a track bar that is in its original location.

So what's the answer? Blaine's steering or Currie? And if Currie steering works really well, even with lots of travel, then why the effort to copy Blaine's steering?

These questions aren't really directed at you personally, mostly just rhetorical.
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