4 link help

Too Far said:
NO, don't make them equal/parallel. Your rear suspension would squat really bad. Desert racers can get away this much squat, but a crawler will have a hard time getting grip.
1. axle separation looks ok. between 10-12" with 40's will work. You will get a little more roll understeer with 12" and it raises your roll axis a bit. If your going for super flexy you may want to go with 10" separation.
2. link separation at frame basically determines the squat characteristics. Equal separation basically gives you no anti squat, and as you move the front of the links closer together you will add anti squat. What to shoot for is largely up to what you want out of your buggy. The front upper link mounts are where I would build in some adjustability. If you give yourself 3 or 4 mounting points you will be able to dial in the squat charachteristics you want, many times you don't really figure out what you want until after the build is complete. I personally don't like rigs with tons of anti squat, so for me I would put my adjustable holes at equal on the highest and 3-4 inches down on the lowest. With your link lengths that will give a pretty wide range of adjustments.
3. upper link length. It seems that around 70% keeps your anti squat equal throughout vertical travel, this is why you see this # talked about so much. Yes, it does induce some pinion angle change. That is the trade off for correct suspension geometry. Many desert/go fast link setups use a length that has the anti squat lessen as the suspension droops out and then get greater as it aproaches full bump. This gives a certain amount of "bump stop" built into the system.
4. lower link angle. you want the virtual point that the upper/lower links make to be around the center of gravity. Having the lower links angle up a bit will help raise this point up where it needs to be. If the lowers are parallel to the ground this point ends up being quite low.

I think that your basically on the right path with your first plan. I would go with around 10"-11" separation at the axle. I would make adjustable mounts for the upper frame with 10"-6" of separation, so you can dial in the antisquat at a later date. I would mount the lower links even with the axle and let them angle up so that the point created by the uppers and lowers is around the center of gravity. I would try and shoot for making this point at the area around the front bumper. The adjustable front upper link mounts allows you to move this point forward and backwards, testing will show what works best with your rig.
At some point you just have to burn it in and see how it works out!
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I'll have to disagree with part of this post--plus, you're kinda contradicting yourself at times.

Parallel links will not make the rig squat. What it will do is have a low ANTI squat number, meaning the suspension won't resist squatting under power. If you had more separation at the frame than the axle, then it would CAUSE it to squat. Low anti-squat numbers work well on crawlers especially, since they won't change how your axle gets traction in loose or variable traction areas. (higher anti-squat can cause a rig to start hopping if it gains/loses traction)

Shorter upper links are what make the anti-squat numbers raise as the suspension compresses, and lessen as it extends.

None of these things will affect greatly how much the rig will squat or not, since he's not going to have tons of power. Traction and predicability is all he'll need to worry about. Drag racers need to dial in their anti-squat to get the greatest grip possible...that just doesn't work the same way on a crawler.

Flat/level links are ideal, in my opinion. Having a convergence point around the center of gravity will end up with quite a bit of anti-squat, and most likely too much roll-steer.

I'll agree with building in adjustability, and tuning it to the driver's wishes. There are too many variables to say there is only one way to build anything. :)
 
I Lean said:
I'll have to disagree with part of this post--plus, you're kinda contradicting yourself at times.

Parallel links will not make the rig squat. What it will do is have a low ANTI squat number, meaning the suspension won't resist squatting under power. If you had more separation at the frame than the axle, then it would CAUSE it to squat. Low anti-squat numbers work well on crawlers especially, since they won't change how your axle gets traction in loose or variable traction areas. (higher anti-squat can cause a rig to start hopping if it gains/loses traction)



Shorter upper links are what make the anti-squat numbers raise as the suspension compresses, and lessen as it extends.

None of these things will affect greatly how much the rig will squat or not, since he's not going to have tons of power. Traction and predicability is all he'll need to worry about. Drag racers need to dial in their anti-squat to get the greatest grip possible...that just doesn't work the same way on a crawler.

Flat/level links are ideal, in my opinion. Having a convergence point around the center of gravity will end up with quite a bit of anti-squat, and most likely too much roll-steer.

I'll agree with building in adjustability, and tuning it to the driver's wishes. There are too many variables to say there is only one way to build anything. :)
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I am happy to yeild to what Carl says. I was having a hard time getting my thoughts down in words.
 
e3f3eef6.jpg


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Maybe that will help you guys see it better
 
Overall, the geometry looks pretty good, but I really think the lower links need to be flush with the bottom of the axle (mounts on front of tube,) and the uppers need to come down the same amount that the lowers do. That will eliminate the ridicu-tall truss/link-mount that the current setup will require you to build.

If your lower links are as high as they are for clearance reasons, think of it this way: If your links are even with/lower than the bottom of the axle tube, you slide all the way over obstacles on your links and the bottom of the housing. If the links are higher (as yours are set up now) you slide on the links, and then get hung up on the huge rock-anchor that you just made out of your axle.

Just my observation/opinion. :)
 
Is your chassis at ride height, and the axle at the height it would be with tires on it?
 
I agree with bryson drop the lower links down to the front side of the axle tube and lower the uppers as well it will help not getting hung up on your rear axle and will definately make it more pleasing to look at.

also your driveshaft will be the lowest part in the rear making it really vulnerable i would like to have my links lower than my driveshaft so if i hit something the links guard the drive shaft per se
 
I Lean said:
Is your chassis at ride height, and the axle at the height it would be with tires on it?
Click to expand...

That is a question that should be asked before any advice is given, because if that is ride height, my advice may not be wise to follow - The angle change in the links would play havoc with important geometry...
 
Carl it is at ride height and axle at trail pressure height.. Racing axle height will be a little higher..

The drive line is a big worry but im going to try running it how it is.

Links mounting on top of axle..
Clearance isn't the big reason for this.. Getting my links flat is the goal..

And with the mounts on top of axle I can tuck the lower link frame mounts up high in the frame ..

Only schedule 40 PVC but I think I will glue some .25 angle iron to the bottom..

Not sure how much compression as in whole axle going up

But where most mount there shocks I have 12 inches up and 12 down maybe a little more that's just lifting one side of axle why dropping the other

I will be running a coil and an air shocks just for fun :)

Coils will be out as far on axle(close to tire) as possible..
Air shocks will be mounted on the lower links


Motor will be 1uzfe..


Also unless things change my roll center??

Or whatever the line that goes through top of tranny bolt is 38.5


I know I'm doing a few things in this build that on paper probably are not right but people trying ideas is how this industry evolves



Ps my lower axle mount will wrap around front of axle and have a few set of holes so I can move lower link down and infront of axle if needed :)
 
Do you have a lot? It doesn't look like it too much in the pics...what it does look like is a ton of side-shift during articulation, which is due to the super-tall roll center you have going on with the links all up so high.
 
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