Suspension design..........

[DsrtJeeper]

While wheeling this weekend I noticed some unique behaviour on my friend's rig as opposed to mine. My rear suspension consist of triangulated uppers and my friends has triangulated uppers and lowers. What happens to my rig is as follows:

Left rear falls into a hole or low spot and this in turn causes the right front to "jack" and lift high in the air. This is supposedly due to the rear lowers transporting energy to the outside of the frame.

My buddy's rig in the same situation does not "jack" in the front nearly as bad. Supposedly; with his rear uppers aimed in towards the center of the rig; the forces are not transported to a specific front corner. I often see this setup on buggies around here. I believe it's called "dual triangulation."

Can anyone shed some light on this subject? Blaine? Also; why don't suspension vendors offer this setup to the public?

[mrblaine]

Originally posted by DsrtJeeper
While wheeling this weekend I noticed some unique behaviour on my friend's rig as opposed to mine. My rear suspension consist of triangulated uppers and my friends has triangulated uppers and lowers. What happens to my rig is as follows:

Left rear falls into a hole or low spot and this in turn causes the right front to "jack" and lift high in the air. This is supposedly due to the rear lowers transporting energy to the outside of the frame.

My buddy's rig in the same situation does not "jack" in the front nearly as bad. Supposedly; with his rear uppers aimed in towards the center of the rig; the forces are not transported to a specific front corner. I often see this setup on buggies around here. I believe it's called "dual triangulation."

Can anyone shed some light on this subject? Blaine? Also; why don't suspension vendors offer this setup to the public?

Start here first- if you hook a tow strap to the front bumper, do you need to also hook one to the rear bumper?

[DsrtJeeper]

Originally posted by mrblaine
Start here first- if you hook a tow strap to the front bumper, do you need to also hook one to the rear bumper?

It depends......Am I flopped on my side again?

The answer is no and now i'm really lost.

[mrblaine]

Originally posted by DsrtJeeper
It depends......Am I flopped on my side again?

The answer is no and now i'm really lost.

No, you are not lost. My point was that you can not arbitrarily transfer energy to a point on the frame as you indicated and have the vehicle act funny just because the arms are attached there.

His suspension pushes on the frame also. Why doesn't his jack?

BTW-Let's discuss jacking first to understand what's happening.

What do you think causes it?

[DsrtJeeper]

Blaine;
I'm not even sure I understand what "jacking" is. I'm hoping that I worded my original post properly to describe what was happening.

I believe the jacking has something to do with power transfer and the leverage it causes. I saw it happen, but I just can't figure it out. He ran the same line with better success and no jacking.

By the way; his rig has outboarded rear shocks with more travel. I think this makes a difference as well.

[mrblaine]

Originally posted by DsrtJeeper
Blaine;
I'm not even sure I understand what "jacking" is. I'm hoping that I worded my original post properly to describe what was happening.

I believe the jacking has something to do with power transfer and the leverage it causes. I saw it happen, but I just can't figure it out. He ran the same line with better success and no jacking.

By the way; his rig has outboarded rear shocks with more travel. I think this makes a difference as well.

Disconnect your shocks. Disco your swaybars. Now, put the front tires against something they can't climb and ease into the throttle. What's gonna happen?

[DsrtJeeper]

"His suspension pushes on the frame also. Why doesn't his jack? "

His rear uppers come together just behind the TC skid. I would think the forces would be aimed more towards the center of the vehicle with less force on one frame rail or the other.

[mrblaine]

Originally posted by DsrtJeeper
"His suspension pushes on the frame also. Why doesn't his jack? "

His rear uppers come together just behind the TC skid. I would think the forces would be aimed more towards the center of the vehicle with less force on one frame rail or the other.

Didn't we just agree that you could pull on one corner of the frame and the whole rig would move?

[DsrtJeeper]

Ooops! I goofed. I'm talking about the rear lowers being triangulated. Think of it this way:
Lift the frame on the passenger side where your rear lower attaches. Now put a jack under the center of the TC skid and lift. What's the difference? Did I word it better that time?

[mrblaine]

Originally posted by DsrtJeeper
Ooops! I goofed. I'm talking about the rear lowers being triangulated. Think of it this way:
Lift the frame on the passenger side where your rear lower attaches. Now put a jack under the center of the TC skid and lift. What's the difference? Did I word it better that time?

You have to answer the disco question first.

[DsrtJeeper]

Originally posted by mrblaine
Disconnect your shocks. Disco your swaybars. Now, put the front tires against something they can't climb and ease into the throttle. What's gonna happen?

The rear will squat and the front will unload. The driver's side front will raise faster due to engine torque.

[mrblaine]

Originally posted by DsrtJeeper
The rear will squat and the front will unload. The driver's side front will raise faster due to engine torque.

almost. If you actually do this and I have, the most pronounced effect is severe body roll from motor torque. To the point of scaring the crap out of you if you try to drive it.

Now, not all rigs will squat in the rear, some will raise and that's the suspension working.

So, what's happening is that resistance to forward movement is be shown by the body trying to rotate around the driveshafts.

The steeper the angle, the worse it is.

Your theory almost makes sense until you get a mental image of the arm angles when TJ's do this the worst. That would be when the left front tire is the highest point and the right rear the lowest point.

That means that the frame is actually being pulled downwards in the left front and working against the right front lower. Then the right rear arm is almost parallel to the frame and the left rear is the most angled. Essentially the springs are letting the motor torque work it's devilry.

[DsrtJeeper]

Aha! Each time it happened; I was in the position you describe. So this only works one way? By one way; I mean the rear passenger side at a low spot and the front driver's side climbing. Like this shot: Jacking

[mrblaine]

Originally posted by DsrtJeeper
Aha! Each time it happened; I was in the position you describe. So this only works one way? By one way; I mean the rear passenger side at a low spot and the front driver's side climbing. Like this shot: Jacking

I'm not going to say that's the only time it happens, it's just the most likely scenario that will stop forward progress.

There are many little things you can do to slow down the effect. The first and most important is try and avoid having your tire in that spot.

Or, if you are like me, you do it on purpose to see how high it will go.

and sometimes you spot your buddies into it just to see how high they will go.

and if you are really good, you can trap more than one buddy

[DsrtJeeper]

I never get my frontend in the air. Right Jamie?

OK....now that we discussed this; what benefits does one get by dual triangulating the rear. It must do something for as many custom buggies here having this setup.

Thanks for explaining the first part; Blaine. My head hurts now!

[DsrtJeeper]

Here is my friend's description of what his dual triangulated rear is doing:

"It changes the roll center, which is the point that the axle pivots around as it flexes. You will notice that with parallel arm setups with a track bar and with a single triangulated setup without a track bar when the axle articulates it follows an arc. most of the time suspensions are setup so that as it flexes the tire dropping also moves outward and the tire stuffing moves in toward the rig. It is also at this time that you will see the rear steer come into play. With a dual triangulated setup the roll is basically only a twisting motion around a certain point, usually around the tcase output area. Think of it this way, picture the axle being attached solid to the rear of the driveshaft, being able to move up and down and also being able to twist around the driveshafts rotational movement. That is the optimal suspension. No bind whatsoever. All forces transfered to a central point around the center of the vehicle. However, no suspension can be perfect, but you do the best you can with the space requirements you have."

[mrblaine]

Originally posted by DsrtJeeper
Here is my friend's description of what his dual triangulated rear is doing:

"It changes the roll center, which is the point that the axle pivots around as it flexes. You will notice that with parallel arm setups with a track bar and with a single triangulated setup without a track bar when the axle articulates it follows an arc. most of the time suspensions are setup so that as it flexes the tire dropping also moves outward and the tire stuffing moves in toward the rig. It is also at this time that you will see the rear steer come into play. With a dual triangulated setup the roll is basically only a twisting motion around a certain point, usually around the tcase output area. Think of it this way, picture the axle being attached solid to the rear of the driveshaft, being able to move up and down and also being able to twist around the driveshafts rotational movement. That is the optimal suspension. No bind whatsoever. All forces transfered to a central point around the center of the vehicle. However, no suspension can be perfect, but you do the best you can with the space requirements you have."

I know that most run dual triangulated to alleviate rear steer, but I don't know how the roll centers affect climbing and jacking yet.

[DsrtJeeper]

Originally posted by mrblaine
I know that most run dual triangulated to alleviate rear steer, but I don't know how the roll centers affect climbing and jacking yet.

Sorry for not being able to put to words the scenerio that had peaked my curiosity. Correct on the rear steer. Here is a flex shot. I couldn't believe his rear tire was pointing straight ahead.

Rio's rig

[mrblaine]

Originally posted by DsrtJeeper
Sorry for not being able to put to words the scenerio that had peaked my curiosity. Correct on the rear steer. Here is a flex shot. I couldn't believe his rear tire was pointing straight ahead.

Rio's rig

That's not that hard to do.

[DsrtJeeper]

The J-arms aren't prone to rear steer? You are actually triangulated more on your lower rears than I am. Your J-arms are farther outboard which is nice to have.

Now; what's the deal with your soft top? It looks like a Besttop Half Top without the tub cover. I need a setup like that. The windjammer lets water and mud through on the side openings beside driver and passenger. This is due to my rear tires flinging dung without the rear flares.

[mrblaine]

Originally posted by DsrtJeeper
The J-arms aren't prone to rear steer? You are actually triangulated more on your lower rears than I am. Your J-arms are farther outboard which is nice to have.

Now; what's the deal with your soft top? It looks like a Besttop Half Top without the tub cover. I need a setup like that. The windjammer lets water and mud through on the side openings beside driver and passenger. This is due to my rear tires flinging dung without the rear flares.

I'd guess the J-arms aren't. Doesn't look like it anyway. I set them up under the premise that the closer I got them to the tire, but better chance I had of not hanging up on them.

The top is a custom creation by me and my upholstery buddy, snaps into the factory door surrounds, goes up under a Safari bikini, and down to an aluminum bulkhead level with the top of the tub.

[Matt Pascoe]

I'm about 90% complete with my double triangulated rear suspension. So, I have no real world experience as to how it will behave but I do have alot of "book" smarts after all of the design and research that went into my suspension.

Perhaps I could help (alittle) by defining some terms that I believe to be true:

Jacking - this is when the suspension tucks under the chasis. ex. front bumper against a wall, add power and the rear suspension walks under the chasis lifting the rear. This can also happen to the suspension when cornering hard (suspension folds under chasis)

Roll center (with 4-link) - this is the point where the upper links converge, typically above the rear diff. This is where the body pivots over the suspension. Roll center is expressed as a height above ground. A low roll center will give alot of body roll, a high roll center will give less body roll. Also a high roll center makes the suspension less willing to articulate and absorb bumps at speed.

Roll axis - This is a line drawn between the upper link convergance point and the lower link convergance point. This is expressed as a slope. A negative slope (sloping down to the front) gives roll understeer, a positive slope gives roll oversteer

I am thoroughly confused as to what a positive or negative roll axis does to handling. I do know that suspension designers strive for a flat or negative roll axis. This is why they double triangulate the links. With paralel lowers and triangulated uppers you will typically have a positive roll axis (unless the rear end of the uppers is higher than the frame end which I dont think is practical to build). I've been told that a positive roll axis makes a vehicle unstable at speed.

AFAIK double triangulated does not directly reduce rear steer, that is mostly a factor of link length and suspension travel (all links travel in an arc). My double triangulated design is giving me quite a bit of rear steer at the limits of suspension travel. So much so that my articulation is limited by the inside upper rear of the stuffed tire pressing into the frame

Heres a pic of the suspension calculator that I've been using, maybe it will help illustrate some of this.


Again, I am far from an expert in this stuff. I'm just passing on some nuggets of info that seemed helpfull to me.

Matt

[DsrtJeeper]

Thanks! Matt. I'm very interested in why you could possibly have so much rear steer. Is your wheelbase stock? My buddy basically welded a crossmember across the frame rails just behind the TC skid. He then attached the lowers to two spots centered on that crossmember. I can get exact spacing if you'd like. The axle mounts for the lowers have been moved outwards slightly and parallel with the ground. He rarely hits a lower arm with this design which is another plus. I believe he runs 4" Procomp coils and they are retained top and bottom in the rear. The upper triangulation is done the same way most comp buggies do. He has the typical rear axle truss with the heims spaced several inches apart on it. I need to check where he attached the frame end of the uppers. His shocks are outboarded.

A quick note about this Jeep.... He drives it daily and has no problems with onroad handling.

[Matt Pascoe]

I dont know that I would say I have ALOT of rear steer, but at the limits of articulation it shows up pretty fast. To me, that picture of Rios rig looks like a fair amount of rear steer, the front edge of the rear tire looks further out than the trailing edge

My WB is ~97". Heres a few pics of my setup:



I think that last picture really illustrates the cause of my rear steer. The compressed lower is almost leval, its longest position. The extended lower is way down in its arc so the effective length is shorter.

I actually got the rear off of jackstands and sitting on its suspension yesterday, hopefully by next weekend I'll be able to see if any of this works...

[DsrtJeeper]

That's looking very nice! The picture of Rio's rig is not doing it justice. The rear steer was nearly non existant in that picture. It's hard to tell with the shadowing. I was surprised to see that your lowers weren't triangulated more. How did you determine the placement of the mounts on the crossmember you welded in?

[Matt Pascoe]

I was surprised to see that your lowers weren't triangulated more. How did you determine the placement of the mounts on the crossmember you welded in?

I placed the crossmember as far forward as possible and still be able to remove my tcase. My thinking with the lowers was the closer I kept them to the frame the better my chance of not bending my crossmember. So, using the link calculator I placed them just far enough from the frame to get a flat (slightly neg) roll axis.

I could have triangulated them more, and I think the increased link length would reduce the rear steer but I would have had to make a much beefier crossmember.

I'll find out pretty soon how it works

[DsrtJeeper]

Will you be at TDS? I belive Rio's rear lowers are triangulated a few inches more towards the center of the crossmember. Maybe this accounts for his lack of rear steer. You've done a great job on your own and i'm sure there will be a host of little tweaks to get it where you want it. That's the fun of it; right?

[Matt Pascoe]

Barely got it done in time for TDS (10pm Fri night ).

Overall I was extremely happy with how it turned out (everything worked! ) Without front or rear swaybars there is slightly more body roll than I would like, but then again, I'm just not used to it yet.



I feel that I have too much rear articulation, in the above pic I still have several more inches of downward shock travel. The rear steer does not show up in a lineal fashion, almost none untill the very last few inches of travel and then it starts showing up fast. So, I'll probably wind up with some form of limiting straps.

One thing that I was VERY pleased with is how well the front and rear suspensions work together. I was afraid that the rear would do all of the flexing but they seem to match each other very well.

Since TDS I have reattached my front swaybar and taken a few trips on the road and was pleasantly surprised to find that its just as stable as when I was leaf sprung SUA. Couldnt be happier with the outcome

Now I've got to get it in some rocks and see how it really performs

[DsrtJeeper]

Matt;
The rig looks very stable. Very nicely twisted up as well. By too moch artuclation; do you mean that you need bumpstops to avoid stuffing your tires into the flares? Take them off!

....and what's with the square headlights?????

[mrblaine]

Originally posted by DsrtJeeper



....and what's with the square headlights?????

You now have met the first requirement for being able to own and operate a coal cart. That being the inability to distinguish a square from a rectangle.

Using your logic, the headlights on your rig are oval.