Triangulating a four link suspension

[Jeeppon]

So when you fully triangulate your 4 link, what exactly happens. The anti-roll bar is no longer used, so does that mean that roll resistance approaches infinity subject to the stiffness of the frame, or that roll resistance is provided entirely by those long soft springs?

[MikeAdams]

Actually- most 3 & 4 link setups use sway bars- or "anti-roll" bars- check out Chet Huffman's trophy truck in the skunk works...without a sway bar and a locked rear end can create some undesirable effects.
I'm sure some of the fabricators on this board can fully articulate the cause and effect- or even do a search- this has been covered before..

BTW- thank you for your service in Iraq!
Mike

[DMSRACE]

Yes, thanks for your service!!!!

[025]

What do you mean by fully triangulating.

[Jeeppon]

Well, I've seen some lift kits that claim to have a "fully triangulated" suspension geometry. Specifically, Full-Traction's long arm kit. They claim that by fully triangulating the suspension, track bars are no longer necessary to keep the vehicle stable in turns. My question is... How? Do does doing this put all the roll resistance on the springs? If so, thats bad, because eventually I'd have long, relatively soft springs to absorb the high speed bumps. Or, does it use increased leverage on the frame to provide the roll resistance?

[silverstateracer]

I think what they mean by triangulated is that you don't need a panhard rod (what they are calling a track rod). The triangulation works to stop body yaw with relation to the axle not body roll (i.e. body won't wiggle side to side). There are ways to control body roll with suspension connection point changes, but I don't think you would want to use it on something being built for max articulation. A track bar adjustment change in Nascar usually results in changes with regards to body roll.

P.S. Thanks for your sacrifice...You're the guys that keep us free!

[Josh_K]

As an interesting side note to this, some of the newest and baddest competition rock crawlers are getting away form the off road style 4 link and going back to a 4 link with a pan hard bar (I call it a 5 link). I seems that it is allot easer for them to deal with off camber lean with this set up and a winch to pull the body down to the axel to eliminate body roll.

Josh

[ntsqd]

In a rock krawler the links are typically very short. Unless the designer understands the concept of the Roll Axis and can adjust it, this makes for a system that will steer the rear end when articulated. Sometimes that's an advantage, but most of the time it causes problems. By going to nearly parallel linkage arms they can reduce or eliminate rear-steer. Then all they have to deal with is the lateral dislocation of the whole axle thru the range of motion. Some have used a Watts Link laid over flat (Matkins Frames). Looks promising, don't know the results but no one seems to be following that lead.

Then again, some gave up on solid axles altogether.
http://www.dock.net/ntsqd/support/SatMorn run1.jpg

I'll second the fully triangulated comments above. I believe what they are saying is that the linkage design does not require any sort of separate lateral locating arm.

[Stephen]

The panhard bar on a rock buggy lets them raise the suspension roll center up to near the CG height or higher so the rigs don't have body roll at all. I've seen pics of them sitting sideways on the tires and still no body roll, or if anything, the body starts to roll up hill if the roll centers are above the CG height.

This is pretty specialized stuff, for most use a triangulated setup works better since it doesn't try to wag the vehicle side to side when the suspension cycles. Most fronts still run a track bar or panhard bar since it's hard to make the steering work properly with a triangulated suspension.

[GOAT1]

Alot of the competiton rock crawlers are using a 3 link and panhard bar set up now instead of the trianulated 4 link. There are two lower links and one upper, mostly parallel in the top view with the upper link offset to one side. It solves alot of packaging and space issues but they mainly do it because that's what Jon Nelson did and it works so good, everyone has copied it. The reason it work is that the offset location of the upper link causes the rear tires to be loaded equally while climping instead of having the right rear squat and left front lift like a triangulated 4-link would do. I hadn't thought of the high track bar helping the side hill capability with the high roll center but that would make sense. It causes the axle to swing funny and I have heard some people dont like that part of it.

[JESSE_at_TLT]

Isn't the parralel 3-link w/panhard on Jon Nelson's "Tiny" just a better execution of an old idea. The suspension didn't look revolutionary to me, but packaging is incredible and they have obviously refined the supsension to suit their purposes. Baker's planning to use this type of suspension on the front-end of our HD2500 project, and he was talking about examples from straight-axle desert-racing trucks of the 80's.

[Stephen]

Yeah, 3 leading/trailing links and a panhard bar isn't anything new, especially for front suspensions. It really shines on the front of a conventional solid axle 4wd because it's easy to match the panhard bar to the draglink and the links package pretty clean and don't have any inherent bind.

[GOAT1]

Yeah, everyone is copying 'tiny'. It is a common road race setup where they can balance the rear tire loading based on the side to side location of the upper link. That is what I have on the front of my Jeep and it works well.

[ntsqd]

Hum, can't say I've ever seen a 3 link/panhard bar arranged road racer with anything other that the single upper link centered.

[Matt Hoffmeier]

Would anyone happen to have a photo of this 3-link type setup? I am planning to dive into a 4-link w/ panhard setup for my jeep's front suspension this weekend. Space gets really tight at the front differential, and the 3-link might be just the ticket.

Thanks.

Matt

[JESSE_at_TLT]

You'll find exactly what you're looking for over at Pirate4x4 (http://www.pirate4x4.com/forum/).

[Outcast]

In addition to the desirable packaging and roll center/axis characteristics, I also believe that panhard rods have become popular in rock crawling because they allow more articulation without binding. With the fore/aft links being parallel, or at least closer to parallel, with the vehicle's longitudinal axis, there is less angle/missalignment in the heims so the axle can articulate to greater extremes before binding becomes an issue.

To answer the original question, I concur that what the lift kit manufacturer is saying is that the triangulated 4-link eliminates the trac-bar or panhard rod that controls the axle laterally. This will eliminate side to side deflection of the axle, as the suspension cycles vertically, that would otherwise be present with a panhard rod. This is more desirable in suspensions that utilize significant amounts of travel.

[Stephen]

There's some pics of my K5 front here:
http://www.offroaddesign.com/customrigs/TopTruck%20K5.htm

It has 3 leading links and a panhard bar, the current iteration is the same configuration with a lower ride height and motor height, with 8" of bump travel. It definitely packages in the tightest space possible.

[MNGSX]

They should be looking at a mumford linkage... With a twist...

On road racing cars it can be set up so that the roll center is actually underground..

Geometry can be changed and you can use the same concept to raise the roll center considerably farther than a panhard linkage...

http://susprog.com/images/Susp23.jpg

The pivot points of the bell cranks behind the pumpkin actually mount to a drop bracket... We dont want that.. 1 ground clearance.. 2 really low roll center...

So flip the idea upside down.. Bell cranks mount up on the frame... for a roll center that could be above the cab depending on the lever ratios..

[ntsqd]

One thing I think may be getting overloked by some is that with a normal crossed over drag link you WANT a panhard rod in the front. Any other lateral locator will result in the axle traveling in a verticle or nearly verticle path while the axle end of the drag link travels in an arc. Can you say "BumpSteer"?

Obviously this isn't a concern with a rear suspension, but I can't decipher from the original poster's posts which end we're talking about.

[smokey]

They should be looking at a mumford linkage... With a twist...

On road racing cars it can be set up so that the roll center is actually underground..

Geometry can be changed and you can use the same concept to raise the roll center considerably farther than a panhard linkage...

The pivot points of the bell cranks behind the pumpkin actually mount to a drop bracket... We dont want that.. 1 ground clearance.. 2 really low roll center...

So flip the idea upside down.. Bell cranks mount up on the frame... for a roll center that could be above the cab depending on the lever ratios..

Now there's an interesting idea! However, I was under the impression that the roll center on a mumford link was at the imaginary intersection of the two arms connected to the axle housing. If these arms were angled up enough to raise the roll center to or above the COG, I don't see how they could still have the down travel required in off road racing. Maybe I'm missing something, please correct me if I'm wrong, because it's a cool concept.
I wonder how a truck would handle that leaned INTO turns...

If you ran control arms from the axle to the opposite frame rail (ie left side of the axle to the right frame rail) connected to an idler arm, with another arm to the bell crank on a mumford link, would the roll center be determined by the theoretical line connecting the axle mount to the bell crank, or by the control arm running to the idler arm?
I hope my description makes sense. I may be way off base, I was just trying to think of a way to make the idea compatible with long travel - even if it would be overly complex...

Thanks in advance.

[MNGSX]

Now there's an interesting idea! However, I was under the impression that the roll center on a mumford link was at the imaginary intersection of the two arms connected to the axle housing. If these arms were angled up enough to raise the roll center to or above the COG, I don't see how they could still have the down travel required in off road racing. Maybe I'm missing something, please correct me if I'm wrong, because it's a cool concept.
I wonder how a truck would handle that leaned INTO turns...

If you ran control arms from the axle to the opposite frame rail (ie left side of the axle to the right frame rail) connected to an idler arm, with another arm to the bell crank on a mumford link, would the roll center be determined by the theoretical line connecting the axle mount to the bell crank, or by the control arm running to the idler arm?
I hope my description makes sense. I may be way off base, I was just trying to think of a way to make the idea compatible with long travel - even if it would be overly complex...

Thanks in advance.

It was a suggestion for rock crawling not for desert running... You DONT want the high roll center in the desert.. Its compatable with alot of articulation not travel... 30" of articulation is different than 30" of travel. As the center of axle is in two completely different places on each scenario..

Whole axle moving 30" vs one wheel up 15" and the other down 15".