Link Suspension Basics

Tinytoytruck

New Member
Joined
Aug 1, 2014
What about a 4 link setup with the panhard rod setup for extra stability or would these systems conflict with each other? I personally see no reason why you couldn't but maybe someone has tried this setup or considered it?
 

jeepinmatt

At least half the people are dumber than the rest
Joined
Mar 24, 2005
Location
Stanley, NC
Not much has changed since 2011...
But since you asked...
-A panhard bar travels in an arc. As it moves up or down, it also moves right or left. The only point at which it does not is when it is perfectly level (parallel to the axle basically).
-In straight up and down travel, a 4 link moves only vertically, and rotates slightly front to back depending on if the links are the same length or not. Right to left motion is constrained by the triangulation of the 4 link.
-The constraining of the right-left motion of the 4 link would bind against the inevitable right-left motion of the panhard bar. Also, the potential front-back motion of the 4 link would effectively be trying to twist the panhard bar, which may or may not matter depending on the type of joints and how much articulation they have.
 

paradisePWoffrd

Recovering Project Junkie
Joined
Nov 5, 2005
Location
Newton, NC
Not much has changed since 2011...
But since you asked...
-A panhard bar travels in an arc. As it moves up or down, it also moves right or left. The only point at which it does not is when it is perfectly level (parallel to the axle basically).
-In straight up and down travel, a 4 link moves only vertically, and rotates slightly front to back depending on if the links are the same length or not. Right to left motion is constrained by the triangulation of the 4 link.
-The constraining of the right-left motion of the 4 link would bind against the inevitable right-left motion of the panhard bar. Also, the potential front-back motion of the 4 link would effectively be trying to twist the panhard bar, which may or may not matter depending on the type of joints and how much articulation they have.

Agreed. What you are requesting is very similar to the factory suspension in a Jeep. If the control arms are parallel the panhard will control side to side motion without binding, but there will be some binding between the upper control arms against rotation. Depending on the setup, this may be minimal however.
 

Falko

Well-Known Member
Joined
Mar 20, 2005
Location
Winston-Salem
-The constraining of the right-left motion of the 4 link would bind against the inevitable right-left motion of the panhard bar. Also, the potential front-back motion of the 4 link would effectively be trying to twist the panhard bar, which may or may not matter depending on the type of joints and how much articulation they have.

Focus on the comment about the joints. Remember this is how most of the modern Jeep suspensions are designed.
 

jeepinmatt

At least half the people are dumber than the rest
Joined
Mar 24, 2005
Location
Stanley, NC
Focus on the comment about the joints. Remember this is how most of the modern Jeep suspensions are designed.
Yep, you can get away with some things if you have bushings, but the bushing will wear out. The 4 link parallelogram in stock jeep suspensions tries to twist the axle when articulated, but the amount is small enough that the bushings absorb it and you still get great flex. I personally am a fan of a 3 link parallelogram style with a panhard bar, as you get very precise handling and great articulation.
 

paradisePWoffrd

Recovering Project Junkie
Joined
Nov 5, 2005
Location
Newton, NC
Yep, you can get away with some things if you have bushings, but the bushing will wear out. The 4 link parallelogram in stock jeep suspensions tries to twist the axle when articulated, but the amount is small enough that the bushings absorb it and you still get great flex. I personally am a fan of a 3 link parallelogram style with a panhard bar, as you get very precise handling and great articulation.

It also helps that the factory panhard has that craptastic joint in it, and the factory control arms can flex
 

Tinytoytruck

New Member
Joined
Aug 1, 2014
I appreciate the replies. I'm kinda in the research / planning stage. I guess I was just over thinking it and got a bit carried away. My mind wanders sometimes. Lol. Anyway I have been reading over this and other write ups on link suspensions. Hats off to the author. This is really the most clear and direct I have read so far.
 

Mac5005

Well-Known Member
Joined
Oct 19, 2005
Location
Rocky Mount
Cliff notes for 4 link.

I shoot for some generic numbers in the calculator. See what fits under the rig and keep going back and forth until I end up with a setup I feel comfortable with. Usually takes about 3 hours of steady back and forth.

A/s 60-80% and no more that 5% change through travel

Roll axis angle of 0, no more than 2 positive or negative

Pinion change less than 4 degrees each direction.

Also need at least 40 degrees of triangulation minimum.

Try to get upper links as high as possible and as parallel to ground as possible at ride height.

Lower links are typically about same length as tire diameter.

Double triangulation is easier to get all the numbers in the calculator to function correctly through the travel.
As well, this keeps the links pivoting on the link bolts rather than using the misalignment of the joint.

The upper link frame mount is one of the most critical locations. Changes in 1/4 mean a lot. When I build the mounts I usually build them with three holes for adjustments to the a/s. Usually one hole for 60%, one for 70% and one for 80%. As you move the upper link higher the a/s drops and you also need to move the mounting hole forward slightly. Usually 3/4" up and 3/4 forward is what it typically ends up being.
 

Mac5005

Well-Known Member
Joined
Oct 19, 2005
Location
Rocky Mount
There is a ton of info that is easy to find about linking the rear of a vehicle and what numbers to shoot for in te calculator.

But when it comes to the front axle, what are some basic geometry numbers to shoot for?

I'm sure some most things carry over from the rear.

Get the uppers as high and as flat as possible and the roll axis angle as close to zero. If using a pan-hard bar, get the center of it as vertically high as practical and parallel to the drag link.

As far as the pinion change, I'm thinking if most are using a double cardan style front shaft, then it is desirable to have the uppers longer than the lowers in order to keep the pinion pointed at the tcase.
So the ideal pinion degree change would be the same angular change as the suspension travel amount.

As far as the anti-squat (a/s) , it would then become anti-dive (a/d) when applying the brake.

But how does the a/s or a/d affect the climbing ability of the front axle when under torque moving forward?

In the rear the pinion rotates upward under torque, and in the front the pinion rotates downward.

So if I'm thinking correctly about all this, and I may be completely wrong,

The higher the a/s % when analyzing a front suspension, is really the amount of torque % that will cause the front suspension to compress?

If that is the case: then a much lower front a/s number would be desirable, and just guessing here a range of 20% to 40% would be comparable to the rear a/s of 60-80%, in terms of how the suspension mechanically extends or compresses itself under torque due to the geometric design?

Looking at images of big name buggies, both rock bouncer and ultra4 stuff. It appears the front links are much closer to parallel that the rear when viewed from horizontal.

Need some help on this. Not trying start a debate on just make it all fit vs using the calculator. Just trying to get a similar range of #'s to shoot for when using the calculator for front suspensions.

Any and all help is appreciated. Hope this doesn't cloud this thread that already includes a great deal of rear link info without having to search pirate for hours. If this spins off and gets dumb, I will gladly start a separate front suspension tech thread.
 

Mac5005

Well-Known Member
Joined
Oct 19, 2005
Location
Rocky Mount
There is a ton of info that is easy to find about linking the rear of a vehicle and what numbers to shoot for in te calculator.

But when it comes to the front axle, what are some basic geometry numbers to shoot for?

I'm sure some most things carry over from the rear.

Get the uppers as high and as flat as possible and the roll axis angle as close to zero. If using a pan-hard bar, get the center of it as vertically high as practical and parallel to the drag link.

As far as the pinion change, I'm thinking if most are using a double cardan style front shaft, then it is desirable to have the uppers longer than the lowers in order to keep the pinion pointed at the tcase.
So the ideal pinion degree change would be the same angular change as the suspension travel amount.

As far as the anti-squat (a/s) , it would then become anti-dive (a/d) when applying the brake.

But how does the a/s or a/d affect the climbing ability of the front axle when under torque moving forward?

In the rear the pinion rotates upward under torque, and in the front the pinion rotates downward.

So if I'm thinking correctly about all this, and I may be completely wrong,

The higher the a/s % when analyzing a front suspension, is really the amount of torque % that will cause the front suspension to compress?

If that is the case: then a much lower front a/s number would be desirable, and just guessing here a range of 20% to 40% would be comparable to the rear a/s of 60-80%, in terms of how the suspension mechanically extends or compresses itself under torque due to the geometric design?

Looking at images of big name buggies, both rock bouncer and ultra4 stuff. It appears the front links are much closer to parallel that the rear when viewed from horizontal.

Need some help on this. Not trying start a debate on just make it all fit vs using the calculator. Just trying to get a similar range of #'s to shoot for when using the calculator for front suspensions.

Any and all help is appreciated. Hope this doesn't cloud this thread that already includes a great deal of rear link info without having to search pirate for hours. If this spins off and gets dumb, I will gladly start a separate front suspension tech thread.


TTT
 

John Fuller

XJ Fanatic!!
Banned
Joined
Jan 3, 2015
Location
Boone NC
There is a ton of info that is easy to find about linking the rear of a vehicle and what numbers to shoot for in te calculator.

But when it comes to the front axle, what are some basic geometry numbers to shoot for?

I'm sure some most things carry over from the rear.

Get the uppers as high and as flat as possible and the roll axis angle as close to zero. If using a pan-hard bar, get the center of it as vertically high as practical and parallel to the drag link.

As far as the pinion change, I'm thinking if most are using a double cardan style front shaft, then it is desirable to have the uppers longer than the lowers in order to keep the pinion pointed at the tcase.
So the ideal pinion degree change would be the same angular change as the suspension travel amount.

As far as the anti-squat (a/s) , it would then become anti-dive (a/d) when applying the brake.

But how does the a/s or a/d affect the climbing ability of the front axle when under torque moving forward?

In the rear the pinion rotates upward under torque, and in the front the pinion rotates downward.

So if I'm thinking correctly about all this, and I may be completely wrong,

The higher the a/s % when analyzing a front suspension, is really the amount of torque % that will cause the front suspension to compress?

If that is the case: then a much lower front a/s number would be desirable, and just guessing here a range of 20% to 40% would be comparable to the rear a/s of 60-80%, in terms of how the suspension mechanically extends or compresses itself under torque due to the geometric design?

Looking at images of big name buggies, both rock bouncer and ultra4 stuff. It appears the front links are much closer to parallel that the rear when viewed from horizontal.

Need some help on this. Not trying start a debate on just make it all fit vs using the calculator. Just trying to get a similar range of #'s to shoot for when using the calculator for front suspensions.

Any and all help is appreciated. Hope this doesn't cloud this thread that already includes a great deal of rear link info without having to search pirate for hours. If this spins off and gets dumb, I will gladly start a separate front suspension tech thread.
DAAIIIIAMMM...trying to learn a little something here and well, ...i'm lost as i've ever been lol. reading stuff is not my strongest at all so maybe that's why...i feel pretty dumb about right now!lol sounds like great info though...don't bother replying to me/trying to make it simpler terms...i probably still don't understand. i learn visually and why school never worked out. sorry to barge in but just learnin and skimming! moving on
 

Mac5005

Well-Known Member
Joined
Oct 19, 2005
Location
Rocky Mount
Copied my post from pirate in this thread Mark Ortiz chassis newsletter-“anti” effects - Pirate4x4.Com : 4x4 and Off-Road Forum



gt1guy;32679058 said:
Usually, we do not speak of anti-squat when referring to the front wheels. Anti-squat means a tendency of the rear suspension to jack up under power, countering the tendency for the rear suspension to compress due to rearward load transfer. The corresponding property at the front is anti-lift: a tendency to jack down under power, countering the tendency for the suspension to extend. Under braking, we can have anti-lift at the rear. The corresponding upward jacking tendency in braking at the front is called anti-dive. All of these can be considered forms of anti-pitch.

Negative anti-lift is pro-lift; negative anti-dive is pro-dive – and so on.

100% anti-squat is the amount of anti-squat that will make the rear suspension neither extend nor compress in forward acceleration. That doesn’t mean the car won’t pitch. It just means it will pitch entirely by rising at the front; the rear won’t go down.

For front wheel drive, 100% anti-lift is the amount that will cause the front suspension to neither extend nor compress in forward acceleration. Again, the car will still pitch, but it will pitch entirely by squatting at the rear; the front won’t come up.

Likewise, in braking 100% anti-dive or anti-lift is the amount that will result in zero displacement at the end in question when braking.

Although linguistic evolution has given us four different terms for these effects, they are all fundamentally the same thing: jacking effects resulting from longitudinal ground plane forces.



I am reading this as follows, if I ignore the effects of turning and load changes described in the original post:

Anti-squat in the 4 link calculator, when used to model the front suspension, could/should be labeled pro-dive.

The forces could/should be labeled as pro-dive under throttle and anti-dive under braking.

Pro-dive could also be referred to as anti-lift, it's easier for me to mentally understand it as pro dive under throttle for the next part.

In terms of travel AS in the rear, it is better for AS to decrease in droop, and increase in bump.

My change in AS in either direction I try to keep in the 10-15% range. This way the adjustable mounting locations change the overall value, and the deviation in travel is minimal.


So if the axle is compressed, while under throttle, the increasing AS would help to push the axle back to static location, making rebound faster.

The same would apply to droop. If the axle is at droop, you want AS to decrease, so that the geometry is not making it harder for the axle to return to the static location while under throttle.

When I think about travel (AS) or pro dive in the front:

When I apply The theory of increasing/decreasing AS at bump/droop from the rear to the front suspension:

It would then be desirable to have the front pro-dive decrease at bump, and increase at droop.

If the front pro-dive decreases at bump, this would aid in the axle rebounding back to static position, and not be sucked up to the bumpstops while under throttle, again making rebound faster.

If the front pro-dive(AS) increases at droop, then under throttle this would help the axle to return to the static location, and not be "stuck" at full droop.

Of course my terms of rebounding faster/slower, are in consideration that shock valving and spring force are the same and not changed.

As well, as pointed out in original post, the actual effect of travel rear anti-squat and front pro-dive is related to the slope of the green line in the calculator. The steep the slope the greater the effect the AS/PD value has on the chassis/suspension.

Thoughts?
 

iwaxmyjimmy

College Web Wheeler
Joined
Mar 10, 2007
Location
Greenville NC
I'm still curious about 3 link front numbers to shoot for, hopefully I'll be linking the front and rear of my JK this winter. The rear I've got pretty worked out on the calculator and I feel like I've got a solid understanding of it. But up front I'm in that grey area for the 3 link.


Sent from my iPad using Tapatalk Pro
 
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