let's talk about 4-links

[N-Smooth]

Double triangulated to be exact...
there really is no easy way to start a discussion on this so i will just hit it head on hopefully. i have been gathering information on 4-link suspension for a while now on PBB mainly and i wanted to actually get in on the discussion without someone calling me a stupid newbie, you know how it goes. anyways, here is what i collected, please chime in and lets talk about links!

why double triangulated? less axle steer than other setups

-DEFINITIONS-THE CONFUSING PART!!!-

-SQUAT/ANTISQUAT-best described by a picture and most of you have probably seen the pictures of a car that display this, i will do my best
-squat or antisquat is what happens when you move forward and your center of gravity shifts to the rear
-squat is when the the rear part of the body moves downward and the suspension moves upward, providing less traction basically because the tires are not being pressed downwards besides with the weight of the rearend
-antisquat is when the rear part of the body moves upward and the suspension moves down, providing more traction because it is driving the tries into the ground
-numbers: 100% antisquat means that the axle will not move up or down during acceleration and 0% means that the rear end will squat down because there is no raising force from the rear suspension
-as you can imagine they both have their ups and downs because too much antisquat can cause bouncing and breakage and too little doesn't provide a lot of traction
-longer links also helps because during suspension cycling they change the antisquat levels slower than short links

-ROLL CENTER-
-the point at which the uppers converge at the top of the axle
-the higher the roll axis the better a rig will handle in off-camber situations because basically the body is being "supported" up higher so there will be less body roll
-also, with a high roll axis doesn't let the wheels compress upwards as easily as a low roll center, because it has to move the body

-INSTANT CENTER-
-take a look at the links from the side and draw a line through the upper links toward the front of the vehicle and do the same with the lowers and the point that they intersect at is the instant center

-CENTER OF GRAVITY(COG)-
-figure it out using this... lots of work!
http://www.jeepaholics.com/TECH/COG/

 

[N-Smooth]

-BASIC GUIDELINES TO DESIGN- (may be opinionated)

-make links as long and flat as reasonably possible
-make the roll axis as high as reasonably possible
-make the triangulation 40 degrees plus
-make the frame mounts as level as possible to the frame so they don't drag
-the more horsepower and tires you have the more vertical separation you need at the axle to control wrap
-place the axle mounts as far apart as possible for stability

-a good way to start a 4link would be to make the links parallel (or close to parallel) to eachother when viewed from the side and make the upper mounts on the frame adjustable (up-down) so that you can tune antisquat. links totaly parallel induces less antisquat and it is a good idea to start that way and change as you go instead of hopping all over the place your first time out and you will have less problems with breaking

-there is a lot of adjustment in link length, for example-
-running shorter uppers makes the pinion slowly point downwards while in droop, but running equal length uppers and lowers make the antisquat increase as the axle droops and the only thing that will stop it is a limiting strap.
-so basically, people run shorter uppers because it uses antisquat for a good bite into the ground and if the axle droops more, the antisquat will not increase... but you must run a limiting strap so that the pinion does not go too far

-some people talk of magical link length of 36" lowers and uppers 25-27"... it is said that the uppers should be 70-75% length of the lowers, whether or not this is true???

 

[Greg]

Do you subscribe to Petersons? Do you have the July '03 Issue? There's a 4 Link article that explains only what you need to know, in simple terms. I think that's the best collection of 4 Link information, considering our use.

Is there something specific you want to discuss?

 

[N-Smooth]

okay that is all that i have right now, lets hear some replies... i will give you a while as it is a lot of reading! the point of this is to learn more because i am not an expert...

on top of that, there is no perfect setup for everyone, and you could tune a triangulated four link into millions of combinations of antisquat/squat and link length etc... but what is important is making one that works at all and then you can make it work well.

 

[Greg]

-some people talk of magical link length of 36" lowers and uppers 25-27"... it is said that the uppers should be 70-75% length of the lowers, whether or not this is true???

In the Petersons article they go over the idea that (If your lower links are pointing to your COG), then the uppers should be 25% shorter. I don't know exactally why, but I would imagine it has to do with keeping your pinion angle close to the same as the suspension cycles up and down.

Then again, I'm going off what I've read & makes sence to me, so I may be wrong. Take it for face value.

 

[Shawn]

-BASIC GUIDELINES TO DESIGN-

I think you get the idea.

Now, go build one and learn even more.

 

[N-Smooth]

Do you subscribe to Petersons? Do you have the July '03 Issue? There's a 4 Link article that explains only what you need to know, in simple terms. I think that's the best collection of 4 Link information, considering our use.

Is there something specific you want to discuss?

i didn't get that petersons, and i have heard good and bad about it. i think that pbb is the best source you just have to read the right threads with the right people. some of those jerks are really smart and can put it in simple terms! i just want to talk about it, hopefully some lights can go on in people's heads cause of what i wrote... but i understand that it is a hard subject to discuss and understand.

 

[Shawn]

-some people talk of magical link length of 36" lowers and uppers 25-27"... it is said that the uppers should be 70-75% length of the lowers, whether or not this is true???

I like them longer,
mine are close to 50".
Tops are about 2" shorter than the lowers.

 

[N-Smooth]

I think you get the idea.

Now, go build one and learn even more.

yeah hopefully soon! i was a leafs man up until i started understanding 4 links a little better. i am going to stick with shackle reverse for the front though. rear links just make more sense to me.

 

[Shawn]

yeah hopefully soon! i was a leafs man up until i started understanding 4 links a little better. i am going to stick with shackle reverse for the front though. rear links just make more sense to me.

This is smart, I was going to go with a link in the front,,, but it just works so well with leafs I just can do it.

Don't over think this idea, when you start to build it, it will all make sence.

 

[Greg]

I'll toss a Monkey Wrench into the general Squat/Anti-Squat theroies....

Ken Shupe (Winner of '02 SuperCrawl & many other Comps) has a pretty standard Comp Buggy. His rear 4 Link (From what I've heard) is setup for alot of Squat and uses a limiting strap to control how far away the axle travels from the frame. The idea is pretty much simaliar to a Drag Car with traction bars. Plant the tires with alot of squat, but put a set limit of where the axle stops planting. Brilliant idea, I think. I don't know if it's still the same.

 

[N-Smooth]

This is smart, I was going to go with a link in the front,,, but it just works so well with leafs I just can do it.

Don't over think this idea, when you start to build it, it will all make sence.

well when i put the leafs under the front of my xj i thought shackle forward would be fine so i did it, not knowing much about shackle reversals. then i thought about it and started reading about links and i decided to go with shackle reversal... it just clicked in my head like a math equation, it all of a sudden works you know.
i do plan on building it soon, but maybe not till after ejs because links in the rear to me means more than just putting them in there. i need to tube out the back if i am going to go with coils.

 

[N-Smooth]

I'll toss a Monkey Wrench into the general Squat/Anti-Squat theroies....

Ken Shupe (Winner of '02 SuperCrawl & many other Comps) has a pretty standard Comp Buggy. His rear 4 Link (From what I've heard) is setup for alot of Squat and uses a limiting strap to control how far away the axle travels from the frame. The idea is pretty much simaliar to a Drag Car with traction bars. Plant the tires with alot of squat, but put a set limit of where the axle stops planting. Brilliant idea, I think. I don't know if it's still the same.

true true, but wouldn't you agree that if you were to build it yourself you would do it differently? just make the upper frame mount have like 3 or 4 holes vertival on the same arc and then adjust it. start with the arms about parallel when viewed from the side because you will have less AS. less AS lets your tires just kind of hang out, it does not apply as much down force, leading to less hopping and breakage of all sorts. if it were me i would do that and then if i wanted more traction cause i felt like it could grab better, i would simply lower them a hole. get it?
your first few times out you could decide what you want from it and adjust it. ken does have a lot of antisquat, i believe they are all on the same plane.

 

[Greg]

true true, but wouldn't you agree that if you were to build it yourself you would do it differently?

Oh, for sure I'd do it diffrently. Adjustable all the way. Just tossing the idea out.

 

[N-Smooth]

Just tossing the idea out.

and i appreciate it because that is how things get said is questioning!

come on more people come talk i know there is more knowledge than this out there.

 

[N-Smooth]

okay here is an idea... any of you that check out this discussion that have a 4link, post a good pic of it from the rear or the side or even post both. i think that seeing it explains it better.

shawn, you have a 4 link so post a pic or two.

i know hickey has links too, but he hasn't chimed in yet... i would actually like to learn more about his link setup being threaded and running bushings... see how it works.

anyway, keep a posting guys

 

[Shawn]

 

[Shawn]

 

[James K]

Shawn what is your seperation at the frame on your uppers?

 

[cyberduke]

okay here is an idea... any of you that check out this discussion that have a 4link, post a good pic of it from the rear or the side or even post both. i think that seeing it explains it better.

shawn, you have a 4 link so post a pic or two.

i know hickey has links too, but he hasn't chimed in yet... i would actually like to learn more about his link setup being threaded and running bushings... see how it works.

anyway, keep a posting guys

Hickey I think is still leafs front and rear. And the left one is probably still broken.

Andy's got one that seems like it will really work well on his buggy that's he's building. No side to side movement at all!. Dunno if he's got any pics though.

-Earl