Triangulated 4 link options

csutton7 said:
BBD built a link set up for BBD1 and he ran a panhard bar and he pulled with it --I dont' recall how many links it was though, but I want to say 4--so in essence it was a 5 link--there should be some pics somewhere on the internut of what he built yrs ago....it was a stout set up that I do remember

and yes like the others stated a 4 link has 4 bars and a 3 link has 3 bars, but in almost every case there's a panhard bar with a 3 link set up--which makes it 4 bars--yes it's confusing, but when talking about link set ups you're talking about how many bars travel from the axle to a point forward or backward----
chris
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Here's some pictures of that suspension for BBD1: Suspension


The triangulated 4-link is nice for lots of travel where a panhard's arc would be significant. But for lesser travel systems it's not so bad. It seems like heavy trucks tend to use a panhard bar to control axial movement, and it works pretty well.
 
I think some of you are mistaking some things as per ability and bar diameter and what it actually does.

Lets say he was pulling 30,000 lbs. . . now he has a 4 link with a trac bar vs leaf springs.. .
He now has 4 solid axle locating devices rather than 2 flat pieces of spring steel wrapped around a bushing with a bolt thru it at each end (in reality you only have 2 mounting points and 1 flat piece of steel locating and keeping the axle under the truck), it's only the main leaf that keeps the axle centered, with the 4 link you really have 4 points locating it.

A 4 link with double triangulated arms like in that picture with that set up will be kinda squirrelly in a street truck and towing.

The best as far as easier is the straight 4 link with a trac bar, and the only way the rear will move side to side is if you mount the trac bar at ride height wrong, if it is mounted level at ride height then at full comp it might have a .25 to .5" difference to the left or right from center and at full drop it might have a .5" diff the opposite way (unless you're looking for teens of axle movement then you might get an 1." to 1.25")

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Supershafts said:
I think some of you are mistaking some things as per ability and bar diameter and what it actually does.
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You need to understand the geometry of the setup as well as the loads involved. Its not as easy as looking at it and eye-balling it.

The 4 link calculator has a force calculation for each link. It uses an outrageous safety factor, but then again peoples lives are at risk if it breaks.
 
The geometry of how it's set up will be the driving issues it has on the road, by eye ball the double triangulated pic is going to be on road offensive.

The diameter of the bar is important also, but if you're not going to enter in the monster jam free style events the bars don't need to be that big. . . .ever seen a ford expeditions driving around on 2 links (5 links total) because the bottom links are gone, its very common. . . As for safety, ever come across the issue of breaking the bottom bar at the front after you make it 4' long and 2" diameter rather than keeping it the needed diameter and short. . . .
Rather have short and needed diameter fold away and break off then rip the rear out of the truck, or rip/bend that axle side out/off and send it spinning into someone else vehicle. . .

When you modify a vehicle like this and god forbid have an accident do to some issue, fed law makes it illegal to modify vehicles without certain procedures like that and after they insp it. . . it's all over.

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Great thread! I am building a pulling truck and wonder if this would apply to the front end also? I am putting a solid axle under my Chevy and I think that a lot of this would apply. Correct?
 
Supershafts said:
The geometry of how it's set up will be the driving issues it has on the road, by eye ball the double triangulated pic is going to be on road offensive.

The diameter of the bar is important also, but if you're not going to enter in the monster jam free style events the bars don't need to be that big. . . .ever seen a ford expeditions driving around on 2 links (5 links total) because the bottom links are gone, its very common. . . As for safety, ever come across the issue of breaking the bottom bar at the front after you make it 4' long and 2" diameter rather than keeping it the needed diameter and short. . . .
Rather have short and needed diameter fold away and break off then rip the rear out of the truck, or rip/bend that axle side out/off and send it spinning into someone else vehicle. . .

When you modify a vehicle like this and god forbid have an accident do to some issue, fed law makes it illegal to modify vehicles without certain procedures like that and after they insp it. . . it's all over.

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so what exactly you are saying?
 
no i didn't open links, i see pictures of bad set ups being used as examples though of better than

I have quite a few books on suspensions, design and engineering, even a few on laws regarding modifications to vehicles for on highway use.
 
what issues? I think it has already been established in the thread that both link geometry and material selection are important
 
There is a few things to consider with a 4 link as far as handling go too. On a parallel 4 link with a trac bar your roll center is wherever the trac bar crosses the center line of the vehicle. Ideally the should be as close to your vehicles center of gravity height as possible but this is hard to do because generally that's about the same height as the camshaft. Triangulated 4 links can be made EXTREMELY strong (Kenworth uses a sort of 4 link on there 8 bag suspensions) but you have to keep the triangulated set (generally the uppers) at a pretty severe angle. The downside to that is it will hinder extreme wheel travel but in your case this shouldn't be an issue as it will be more of a street truck. It's hard to explain without pictures but with a triangulated setup you can kindof put your roll center wherever you want by changing link angles (up and down looking at it from the side). The closer you can get your roll center to your center of gravity height the better it will handle. If you can get you VRC (vehicle roll center, found by connecting your front and rear roll axis') at the same point as your center of gravity youd be golden. My opinion is do a triangulated 4 link.
 
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I'm a big fan of Ballistic Fab. They have about any mount you can think of and they can custom make brackets.
 
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