Learn me - Triangulated 4 link

I'm mocking up the triangulated 4 link on the '49. Need input from anyone familiar with this. This is a triangulated not a parallel but I don't know if the top and bottom bars should still be parallel or not. You can see in the photo they are not. I could drill the lower axle end mounts and move these lower bars up a bit if its an issue, Im just not sure it matters with a triangulated setup like this. This is a full squat as the axle is actually welded to the frame during this setup stage to keep it properly aligned. I have to get some 3/16 plate to box the frame so I can actually mount the ends, they are just tacked to the frame right now and I'll need to build new mounts for the axle end of the upper link as the universal mounts I have are not ideal, they way they are sitting right now will put the joints in bind when it moves.

Some of my drag racing friends chimed in elsewhere and it looks like Im fine but I'll need to calculate the IC once Im far enough into the mockup to get proper measurements.    My brain just got scrambled with parallel 4 links and I suddenly couldn't remember if triangulated needed to keep the bars parallel or not.

Do not do it unless this is drag dominant.  The Fox Mustang is a triangulated four link and the arms are too short and it's bindarifically bad. 
 

Id prefer a parallel 4 link with a panhard rod by a lot.

AnthonyGS (Forum Supporter) said:

Do not do it unless this is drag dominant.  The Fox Mustang is a triangulated four link and the arms are too short and it's bindarifically bad. 
 

Id prefer a parallel 4 link with a panhard rod by a lot.

Oh I dont plan to go away from the triangulate 4 link, just making sure I wasn't missing something with the way these bars were lining up.  I know everyone has their preferences.  The goal of this one is not anything sporting and this setup is fairly standard in old trucks, it works well.

The rear roll center will be determined where the angled bars intersect.  In your case, this would be (in my opinion) a very high rear roll center.  I would prefer to angle the lower bars.

The instant center for "anti squat" will be determined where the top and bottom bars intersect.  I prefer to keep the lower arms horizontal (parallel to ground), because.....

.... Angling the lower arms UP at the FRONT to increase anti-squat, introduces roll steer.

All the while, there is a lot of binding in this design because of the different arcs of motion that the axle tubes will not twist around.  Rubber bushings will "hide" a lot of the binding, poly or rod ends will not.

There isn't really a magical win with this, which is why I much rather have a three link and a panhard.

AnthonyGS (Forum Supporter) said:

Do not do it unless this is drag dominant.  The Fox Mustang is a triangulated four link and the arms are too short and it's bindarifically bad. 
 

Id prefer a parallel 4 link with a panhard rod by a lot.

Misguided. Once you are free to articulate all points, it works rather well in all aspects. But in the same breath, a wishbone should be utilized jst to avoid the little amount of sway possible.

Ranger50 said:

AnthonyGS (Forum Supporter) said:

Do not do it unless this is drag dominant.  The Fox Mustang is a triangulated four link and the arms are too short and it's bindarifically bad. 
 

Id prefer a parallel 4 link with a panhard rod by a lot.

Misguided. Once you are free to articulate all points, it works rather well in all aspects. But in the same breath, a wishbone should be utilized jst to avoid the little amount of sway possible.

Came here to say this, using bushings that can only rotate on 1 axis is the first big mistake I see, and the kind of mistake that has given this suspension design its undeserved reputation as a bind-ridden disaster. If the joints are free to rotate on all axes then this is actually the best suspension linkage design for solid-axled offroaders (often seen on KoH/Ultra4 trucks).

You want to keep the pinion angle constant, so it's a bit like designing a double wishbone suspension with zero camber change, parallel arms with equal length would be the easiest way to achieve that in theory, but in practice there are usually compromises...

Common problem for binding to arise when folks swap in poly bushings on triangulated 4 links. Often it's just the top 2 links that are angled, so if you replace those with spherical bearings the system can work very well. 

maschinenbau said:

Common problem for binding to arise when folks swap in poly bushings on triangulated 4 links. Often it's just the top 2 links that are angled, so if you replace those with spherical bearings the system can work very well. 

The binding occurs when the 2 ends of the joint aren't kept in the same plane.  It's very easy to mess this step up.  In my mock up they are not in the same plane but I know that and that's why Im building new upper mounts to adjust.   But agreed that if you cannot, due to packaging constraints, keep the joints aligned then a spherical bearing is the fix.  Its my plan B but I don't think I'll need to go there as I have the space to get them aligned correctly with some properly made mounts.

As posted: not sporty, just a truck = It really won't matter as long as you're not so far out of wack that problems exist before it even moves.

To make it work well: Yes you want to be close to parallel at ride height....If it were me I'd be setting this up at ride height and not axle to frame like you are (but it understand the easy of it). The kit you're using looks to have some decent length to the links (compared to a fox body or G body) and that's going to help a lot in minimizing bind while increasing movement and performance characteristics. With my G body and going after performance I've arrived at a setup with the uppers nearly level and the lowers with a few degrees up to the front. The lower angle gives it rear steer which gives me the feel and rotation I like on track. Street setup you'll want to be closer to, or level so that you minimize bump and/or roll induced steering going on. Spherical bearings are great for movement and I didn't notice much additional NVH with the Ridetech stuff. For a driver...not needed.

Asphalt_Gundam said:

As posted: not sporty, just a truck = It really won't matter as long as you're not so far out of wack that problems exist before it even moves.

To make is work well: Yes you want to be close to parallel at ride height....If it were me I'd be setting this up at ride height and not axle to frame like you are (but it understand the easy of it). The kit you're using looks to have some decent length to the links (compared to a fox body or G body) and that's going to help a lot in minimizing bind while increasing movement and performance characteristics. With my G body and going after performance I've arrived at a setup with the uppers nearly level and the lowers with a few degrees up to the front. The lower angle gives it rear which is gives me the feel and rotation I like on track. Street setup you'll want to be closer to, or level so that you minimize bump and/or roll induced steering going on. Spherical bearings are great for movement and I didn't notice much additional NVH with the Ridetech stuff. For a driver...not needed.

Thank you, that is really what I was looking for, making sure I wasn't headed down the wrong path in the mock up.   I understand we all have different goals and expectations so others are providing great input for what they would want their vehicle to do but this setup should be more than appropriate for the intended use of the truck.

Agreed ride height setup will be best.  All of this mockup was just to get a feel for where/how things will fit.   Next step is to pull it all back out and box the frame now that I know where it needs to be boxed.  When I do that I will probably solid mount the axle again but with some spacers to get to ride height.   This thing will be dropped and bagged so ride height wont be too far off the frame but I'm aiming for enough that I wont have to notch the frame so Im still mulling over exactly where I want to set it.  Right now my uppers are up in the back and lowers are level so contemplating your setup I think I will be much closer to that with level uppers and lowers angled up to the front once at ride height.

SkinnyG (Forum Supporter) said:

Rubber bushings will "hide" a lot of the binding, poly or rod ends will not.

Soft bushings minimize bind. Hard bushings maximize bind. Rod ends eliminate bind.

I understand that it's not a performance build, but (if it were mine) I'd probably still be looking at something more like simple swaged tubes with Johnny joints at both ends.

JThw8 said:

The binding occurs when the 2 ends of the joint aren't kept in the same plane.

Aligning the mounts to the bushing axis is all that's required to eliminate static bind, but they don't actually have to be co-planar to do so. Dynamic bind through the range of suspension motion will happen no matter how you orient the bushings. Reducing bind means minimizing the amount of non-axial motion the bushings encounter in both 1 and 2 wheel bump situations.

For example: If you orient all of the bushings parallel to the axle, there will be no appreciable bind in 2 wheel bump. However, it will maximize 1 wheel bump (and roll) binding. By comparison, orienting the bushing axis perpendicular to the link tube, parallel to each other, and co-planar in twist, will result in more 2 wheel bump bind but less 1 wheel bump bind.

While the roll center will be high by performance standards, having it that way also won't affect the kinematics of a solid axle the same way it does an IRS... Which is part of the reason it works just fine for truckish things.

JThw8, what are you doing for side to side control?  Panhard bar?

Triangulated 4-link suspension can handle its own lateral control, no panhard bars or z-links needed.

In reply to GameboyRMH :

Yep, that's the whole point of them - so OEM's can save cost by having one fewer link. 

GameboyRMH said:

Triangulated 4-link suspension can handle its own lateral control, no panhard bars or z-links needed.

There's a load-bearing "can" in there... The answer could be "nothing beyond the four links themselves" or "panhard" or "watts" or other stuff beyond those solutions.  Bushing / joint compliance plays into this.

Driven5 said:

SkinnyG (Forum Supporter) said:

Rubber bushings will "hide" a lot of the binding, poly or rod ends will not.

Soft bushings minimize bind. Hard bushings maximize bind. Rod ends eliminate bind.

Agreed. However, (and I may not have been clear in my writing of this), if the movement is such (say, in a one-wheel bump for instance) that the axle tube itself is actually trying to be "twisted" by the motion arcs of the links (that is, one axle tube end needs to be rotated because of the link movement and the other is held stationary), rod ends will not eliminate that.

For the OP's intended purpose, it will all work "good enough." For an all-out race car, probably not the optimal.