Panhard with Links

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Panhard with 3 or 4 Links?

With a Panhard parallel link Suspension I see people running 3 links and some running 4 links.

What are the pro's and con's 3vs4 links?
I read through all the suspension pages and search the internet but I couldn't find the information I wanted. I was hoping to get some expert advise.

The only thing I can think is that 4 links are stronger where 3 links have less binding, hence the 4 link birdcages with torque arms.

Looks to me 3 links do not supported enough.
If the 3rd link is in the middle I guess it could be strong enough


But when the 3rd link is near the vertical over the other mount would this put a huge amount of stress in the links and axle housing.
I'm looking at it like a tripod if you put the 2 legs right next to each other it would not be as stable.
I seen a lot of rock buggies set up like this, I've even seen where a JK or TJ actually just remove one of the upper links to get more travel.
Maybe it is just the fact they are so over built it doesn't matter?




Wouldn't 4 links be stronger



One more question,
Is there any reason everyone puts the 2 links on the bottom and 1 on the top instead the 2 links on the top and 1 on the bottom.
Is it a clearance issue or strength issue?
 
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Zambo

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Is there any reason everyone puts the 2 links on the bottom and 1 on the top instead the 2 links on the top and 1 on the bottom.
To clear the driveshaft?
 

Chris_Wilson

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If you use 4 roughly parallel links plus a panhard link, and the caster changes as the suspension cycles then what happens in the situation where one wheel is drooped out and the other is fully compressed? The front axle tries to twist up like a torsion spring. If the bushings are all metal (shpetrical/heims) then there is nothing to give and it will restrict articualtion and/or flex something that should not flex. If it's rubber or soft bushings then the bushings will take up some of this. You could design the links so there is no caster change as it cycles but this might present some packaging issues.

One solution is to only use two parallel links on one side, a single link on the other side plus the panhard.

Or do a 4 link with either the upper or lower links configured in a V shape so they are only controlling axle rotation at a single point (or two close points) instead of at each end of the axle. Now if you do this you don't need a panhard link. But then you have a steering problem (massive bump steer) because the stock steering was designed with the axle sideways motion (prescribed by the arc of the panhard) taken into account. If you eliminate this side motion then you need to design a steering linkage that also cycles without side motion. Common solutions to this involve bell cranks and steering push/pull arms that run forward to the axle parallel to the parallel link bars. Bell crank on the housing to control the tie rods and bell crank at the back of the link bars to shoot the steering link forward to the steering box (or put the steering box at the back of the link bars and fanagle the steering column back to it. It gets complex but there are many examples of this being done very well.
 

Zambo

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If you use 4 roughly parallel links plus a panhard link, and the caster changes as the suspension cycles then what happens in the situation where one wheel is drooped out and the other is fully compressed? The front axle tries to twist up like a torsion spring. If the bushings are all metal (shpetrical/heims) then there is nothing to give and it will restrict articualtion and/or flex something that should not flex. If it's rubber or soft bushings then the bushings will take up some of this. You could design the links so there is no caster change as it cycles but this might present some packaging issues.

One solution is to only use two parallel links on one side, a single link on the other side plus the panhard.

Or do a 4 link with either the upper or lower links configured in a V shape so they are only controlling axle rotation at a single point (or two close points) instead of at each end of the axle. Now if you do this you don't need a panhard link. But then you have a steering problem (massive bump steer) because the stock steering was designed with the axle sideways motion (prescribed by the arc of the panhard) taken into account. If you eliminate this side motion then you need to design a steering linkage that also cycles without side motion. Common solutions to this involve bell cranks and steering push/pull arms that run forward to the axle parallel to the parallel link bars. Bell crank on the housing to control the tie rods and bell crank at the back of the link bars to shoot the steering link forward to the steering box (or put the steering box at the back of the link bars and fanagle the steering column back to it. It gets complex but there are many examples of this being done very well.
The other way you can get rid of bump steer is to go full hydraulic steering. You just have to run hoses down one of the link arms.
 

Chris_Wilson

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The other way you can get rid of bump steer is to go full hydraulic steering. You just have to run hoses down one of the link arms.
Yes, just make sure you keep a solid mechanical link between the two wheels. This is the route I'd go (full hydraulic but with a real tie rod to link the wheels to each other). Had full hydro steering on my boat and it was great. Without the mechanical link between the wheels the toe will wander just like the steering wheel will not stay centered.

As far as the original question, the setup using two parallel links on one side, a single link on the other side, plus a panhard is plenty strong if you design it right. This is the cheapest route to a big travel, big articualtion coilover setup for a rock crawler IMHO. Also in my opinion, for a go fast rig, it's worth the effort to do a design that eliminates the panhard and deal with the steering. I think full hydro steering would work great on a desert racer. Anyone racing with this setup?
 
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I think he is talking about Axle steer the axle rotating not Bump steer tie rod length change. I plan on going full Hydro.

The binding is what I've always afraid of as one moves up and moves one down they want to twist in opposite directions.
I guess it works in stock vehicles like on TJs because they use rubber joints and the arms are not that stiff.

I like the Panhard design a little better than the triangulated 4lin.
The roll center is easier to modify plus seems to me a panhard would be stronger loaded in the same direction as mounted.
And you don't have the 2 upper links getting in the way of the engine.


Thanks for clearing up 3 vs 4 links

Last question on this.
Would it be stronger to have the single link in the middle of the axle?
The middle sound like it would be stronger to me.
Don't take into account fitment. The compromises will come later.


Thank you
~Justin
 

Zambo

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I think he is talking about Axle steer the axle rotating not Bump steer tie rod length change. I plan on going full Hydro.
No, he was describing the problem you run into if the front axle goes straight up and down. With an angled steering linkage, you get massive bump steer unless you have a panhard bar running parallel to the steering linkage.

The full hydro steering I'm talking about is accomplished with a steering rack mounted on the axle and tie rods going to the knuckles, so no toe change.
 
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