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Parallel 3 link with panhard or radius arm/ladder bar with panhard?

BlueBlazer

BlueBlazer

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Which do you guys like best and why. I do not want to run a 4 link because of space constraints on my rig, so 3 link or radius arms is the way I want to go. If you guys could give me some advantages/disadvantages and maybe some tips on the design I would appreciate it /forums/images/graemlins/thumb.gif
 
I prefer a 3 link to radius arms (assuming writsted) just due to the jacking and caster issues for the front. 3 Link lets you have some control over jacking (anti-squat/dive) and torque reactions (using asymetric top link).

Down side is more cost/fab due to more link ends. I've considered wristed radius arms just for simplicity and cost, but doubt I would go that route when it came down to it. Of course I still have not gotten my rear links done yet due to one problem after another, so hopefully someone with more "real" experience can provide more insight.
 
I have heard of wristed radius arm ends, but have never seen any. Do you have a link with pictures or anything? This is for the rear of my K30 by the way. Its shortened 21" and there is nothing but a fuel tank behind the cab. It has a doubler behind a 465 and NA 6.2. The ladder bar to me seems nice because all I would need is one 1 1/4 heim at the front of the ladder bars and two on the panhard bar and I could run bushings on the axle end, thus saving a lot on joints. Is the jacking effect really that bad I wonder? If it works well on a lot of fronts, I wonder why its not used as much in the rear? Any other comments from any other link suspension gurus?
 
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Which do you guys like best and why. I do not want to run a 4 link because of space constraints on my rig, so 3 link or radius arms is the way I want to go. If you guys could give me some advantages/disadvantages and maybe some tips on the design I would appreciate it /forums/images/graemlins/thumb.gif

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Front or rear suspension we are talking about here?
 
Rear suspension, I was hoping I would see a response from you, your rig is absolutely awesome and I hope you dont mind I have borrowed/will borrow a few ideas from looking at your rig.
 
Wristed radius arms are exactly what Brook runs on the front of the Freak. They seem to work best in the front (as opposed to rear) as long as you don't have issues with caster changing. The only real problem is anti-dive may cause jacking on hard decel (street) or extreme angles on decent. Obviously a strap can correct much of that.

I would be much less inclined to run a rear wristed radius arm since the IC will always be right at the front joint. This typically leads to high anti-squat which is generally not considered ideal. With a third split link you can control the intersection point and provide a "virtual intersection" by changing vertical separation on one end or the other (usually the frame end). Anti-squat is a bigger issue in the rear due to throttle on climbs, but again, you can use a strap, and some competitors handle VERY high anti-squat successfully.

3 link rear can also have more control over roll axis angle, though not as much or easily tuneable as a 4 link. On the other hand, roll axis height is easier to control/tune due to the drag link.

The other problem that can come up is torque roll, and an asymetric top link can be used to counter that to a small degree, where a rear radius arm can't.

I've got similar problems to what you appear to have. My tank is in exactly the wrong location for a traditional or double 4 link. Another option I've considered is the 4 link design with roughly parallel outboard uppers and triangulated lowers meeting at the frame. Retains much of the benefits of a traditional 4 link (like tune ability) and the drawbacks (like roll axis that changes dynamically). But it can also be a bit more trouble to get a higher roll axis if that is important to you.

That's about all I can think of based on my research. If I've made any mistakes or oversights (I'm no expert) I'm sure they will be corrected…
 
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Rear suspension, I was hoping I would see a response from you, your rig is absolutely awesome and I hope you dont mind I have borrowed/will borrow a few ideas from looking at your rig.

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Im not so good at putting it into type like baddog, but he pretty much has it covered anyway. I would never do radius arms in the rear of a truck... Maybe in a sami (80" wb), but nothing longer.

Like he said. Too much antisquat.

I would be much more inclined to do a parallel 4 link with panhard. Infinate instant center = no anti-squat problems

Glad you like the truck... expect some updates this winter.
 
OK, so radius arm idea is out. Now if I go parallel 3 link, where should I put the upper link? Does it matter where really as long as I get enough seperation to control the pinion? Can I use smaller joints on it because it will be taking less stress (or will it take less stress)? I am going to have to do some measurements and run it through some calculator to see what I get. Thanks for the advice thus far and keep it coming /forums/images/graemlins/thumb.gif

Edit:

Brook, does the seperation of your triangulated upper links hold the axle in place laterally pretty well? If I can get away with a setup like yours that will locate the axle well, I think I can pull that off pretty easy. Whats the advantage of using bushings besides cost? Your setup obviously doesnt bind much looking at your pictures. Do the bushings where out fast when they see side loads like your 4 link is subjecting them to?
 
Yes location matters. On the upper 3rd link you can offset it to allow for a centered roll axis. I am not that familiar with the 3 link geometry or I would be more help.

I say screw it, prove em' all wrong with a one link.
 
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OK, so radius arm idea is out. Now if I go parallel 3 link, where should I put the upper link? Does it matter where really as long as I get enough seperation to control the pinion? Can I use smaller joints on it because it will be taking less stress (or will it take less stress)? I am going to have to do some measurements and run it through some calculator to see what I get. Thanks for the advice thus far and keep it coming /forums/images/graemlins/thumb.gif

Edit:

Brook, does the seperation of your triangulated upper links hold the axle in place laterally pretty well? If I can get away with a setup like yours that will locate the axle well, I think I can pull that off pretty easy. Whats the advantage of using bushings besides cost? Your setup obviously doesnt bind much looking at your pictures. Do the bushings where out fast when they see side loads like your 4 link is subjecting them to?


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I would like to have more angle (when looking at the rear suspension from the top) but Its never caused any real problems. I drive my truck at high speeds alot, and have never noticed any poor handeling. I run it in washouts and the like, and abuse it pretty regularly by sliding into ruts. and its never broken, or split out bushings. I also have never "HAD" to replace any bushings, but I have replaced a few that were becoming loose, and had split the flanges. There are really no side loads in a 4 link. All the load is transfered through the links axially. The links should only see compression and tension loading as far as typical suspension movement is concerned. Side load can be induced by external factors though. (sliding sideways into a stump, etc)

Heims or JJ's will provide a more positive feel, and put less stress on the link brackets, but they are 5 times the cost, and dont always last any longer.

Im going to put threaded ends on my rear links this winter, just cause I've got the stuff laying around, and I'd like to get a tad bit more articulation out of it. Should relieve alot off stress on the bushings.

If I was doing a parallel 3 link in the rear, I would put the third link as close to the center of the axle as possible. I would also build my panhard mount on the axle as tall as practical.
 
So do you think heims at one end and bushings on the other would work well?
 
I also run bushings on the frame side of both of my 4 links. The rear 4 link upper links have "split" the outside bushing for the second time (it splits on the shoulder of the outside bushing) I believe this is due to heavy slamming into berms/ ruts. I've discussed it with some fabricators and I may go delrin (selflubricating-hard plastic) for those upper link bushings.
 
What do you guys think if these bushings? Would you have any problem running them at both ends or would you run them just at the frame end? Are they strong enough for a 5500-6000 lb rig?

Blue Torch bushings
 
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What do you guys think if these bushings? Would you have any problem running them at both ends or would you run them just at the frame end? Are they strong enough for a 5500-6000 lb rig?


I wouldnt run those on the lower links, either end. They would be fine on the uppers, but why? It takes away all the reasons to use bushings. (cost)

for another couple bucks you could just get hiems.
Blue Torch bushings

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I guess I was under the impression that the smaller heims do not hold up very well, and its a much bigger price jump to the 1 1/4 heims. How are the bushings you run much stronger? They are 9/16 bore correct? Maybe I am missing something.
 
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I also run bushings on the frame side of both of my 4 links. The rear 4 link upper links have "split" the outside bushing for the second time (it splits on the shoulder of the outside bushing) I believe this is due to heavy slamming into berms/ ruts. I've discussed it with some fabricators and I may go delrin (selflubricating-hard plastic) for those upper link bushings.

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If I understand correctly you are tearing the flanges off the bushes? If so, I don't hold much hope in a harder material curing the problem. One option you might explore would be to have the body OD of the bushings made barrel shaped. That would allow for the misalignment that's wiping out the current flanges.

Mostly what I see in the dez race trucks that use bushings at all is that they are at the frame end of the lower arms only. The axle end of the lowers and all of the ends of the uppers use SRE's. Usually the arms are quite wide at the bushing end. I'm speculating that they are using the end width and the bushing to keep the arm from twisting under the load of the mid-length mounted coil-overs, something most crawlers would not need to worry about (unless Sniper-esque lower arm shape).
Some of the bushes are made of Acetal (Delrin, Turquite, etc.), others are UHMW PE or graphite impregnated nylon. The last option would have me worried about Cold Flow. Acetal can have mild UV issues, so use the black and not the natural color.
 
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