Compilation: FRONT Link suspensions, lets talk comparisons!

[BadDog]

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I want to start a compilation of various topics relevant to those who are building serious off road rigs. Lots of stuff is touched on here and there, but finding it and putting it all together can be a problem. Lets try to get some of this stuff grouped together in one post. This is one such attempt among several. Lets try to keep this very focused and tech rich. NO POST PADDING! If you don't have something to add, please don't post fluff like the typical "that's cool" or similar having adding nothing relevant to the discussion.


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Just like for the rear suspensions, lets try to compile all the data on basic FRONT link suspensions here. Lets talk about (and define clearly) the following in terms of FRONT suspensions:
1) Conventional 4 link (triangulate upper - point on top of diff, parallel lower)
2) Double Triangulated 4 link, Reverse 4 link (triangulated lower - point at chassis end, parallel upper)
3) Parallel 3 or 4 link and track bar
4) Wristed radius and track bar
5) Wishbone upper with parallel lower
6) Whatever I forgot…

I can't tell you how many times I've heard people use the wrong (or ambiguous) terms when referring to a link suspension design. For instance, incorrectly calling a wishbone upper 4 link a "3 link". Lets establish definitions and stick to them so that we have a common vocabulary and frame of reference.

Those with convenient access can post links to the "Link Calculator" spread sheets and web pages.

Lets see if we can get all the basic "layman" descriptions of the various pieces in one place. Things like Roll Axis, Jacking, Torque reaction, "Instant Center", and Anti-Dive. Lets look at them (and describe how to find them!) for each of the primary link arrangements. Much of this will be very similar to the "rear suspension" compilation, but the effects change, like anti-squat becomes anti-dive. Lets mostly focus on the differences in front suspensions.

What are the bad characteristics of each? Things like jacking or binding and considerations/approaches to deal with them.

What about good/bad habits of positive/flat/negative roll axis angle?

What about good/bad characteristic and compromises of roll axis height?

Good and bad of anti-dive?

Clearance issues?


So, lets compare and contrast. Nothing but FRONT suspension discussion on this thread. Lets keep this tightly focused and VERY tech rich. No post padding and no "that's cool" but otherwise empty posts PLEASE.

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Let's keep this technical! Don't respond with "I know a guy who runs "X" and it works great, so that's what I would run" type of stuff. Tell me what you think is best and why. Know a guy who runs it is fine for a start, but tell me what makes it so great you would do the same thing…
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I've got lots of thoughts on these I'll add as I get time, but I'm already running out of time starting these compilation posts.

 

[bgreen]

Well, I finally ponied up so I could post in this Forum, and give my .02 on a few threads.

I'm really pleased with the wristed radius arm and panhard in the front of my truck. It handles great, and has been able to keep up with the rest of the truck just fine, in every situation I've put it in. I do notice the side to side axle movement caused by the panhard, but its not enough to cause any problems. The strenth has been fine, as far as only having two mounting points locating the axle for and aft. I've beat it into ledges on several occasions, and generally abused it as much as possible. The only problem I have had is with bending the passenger side arm, but that was most likely choice of material, and the design of the arm itself.

Anti-Dive seems to be a non-issue.

 

[ntsqd]

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1) Conventional 4 link (triangulate upper - point on top of diff, parallel lower)
2) Double Triangulated 4 link, Reverse 4 link (triangulated lower - point at chassis end, parallel upper)
3) Parallel 3 or 4 link and track bar
4) Wristed radius and track bar
5) Wishbone upper with parallel lower
6) Whatever I forgot…

I can't tell you how many times I've heard people use the wrong (or ambiguous) terms when referring to a link suspension design. For instance, incorrectly calling a wishbone upper 4 link a "3 link". Lets establish definitions and stick to them so that we have a common vocabulary and frame of reference.


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I think we'd better start with the vocab first. To me any linkage with 4 links and 8 total pivots is a 4 link. If it's missing one pivot point it's not a 4 link. If there are 3 links and 6 total pivots it is a 3 link. Orientation of the links (i.e.: upper converging, lower converging, both converging, both parallel, upper parallel - lower diverging, etc.) means nothing to this definition, it's useful only to further describe the linkage layout.
If it has a track bar or panhard bar, which ever you want to call it, then it is a 3 link or a 4 link with a track/panhard bar. A 4 link w/panhard could also technically be called a 5 link, but a 3 link w/panhard can NOT be called a 4 link.
Radius arms are technically a 2 link w/panhard, but since there's really only several variations on a single design I think "Radius Arm" is more appropriate.