Flexing the 3 link (10 Viewers)

[4WheelUnderground]

The 4wheelunderground encyclopedia is good but does make some oversimplifications I don't agree with, namely the idea that a non-parallel 4-link is a glorified radius arm setup. Yes, parallel links would avoid the links trying to twist the axle through 5 feet of travel, but correctly designed link geometries (model the rear of your 80 if you don't believe me) have very little pinion change through their usable travel. Radius arms, by definition, are just swinging the axle around the radius drawn from the lower control arm frame mounts.

I don't remember writing that. Can you please copy and paste the section you're speaking of? From what I remember it isn't a non-parallel 4link that is a glorified radius arm its 4 equal length uppers and lowers that are parallel that are. If all arms are equal length and parallel then during articulation one side of the axle is twisting against the other. If I failed to make that clear to the reader then I certainly take blame for it. Sorry in advance.

 

[Booger weldz]

Oh really. Please please please explain. I'd love to hear this.

I alReady asked. Not even a whisper...

Maybe the issue is you cant buy it at 4wheelparts and bolt it on with home depot tools?

 

[Booger weldz]

The paralell 4 links i build for the airbag lowrider trucks bind at about 7" of articulation when rigidly mounted. The tacks snap off the axle housing w symetrical 24" links perfectly paralell when flexed on a mockup.

I don't remember writing that. Can you please copy and paste the section you're speaking of? From what I remember it isn't a non-parallel 4link that is a glorified radius arm its 4 equal length uppers and lowers that are parallel that are. If all arms are equal length and parallel then during articulation one side of the axle is twisting against the other. If I failed to make that clear to the reader then I certainly take blame for it. Sorry in advance.

 

[4WheelUnderground]

And just so everyone knows I didn't write one paragraph of that article with out consulting a professional engineer that specializes in vehicle dynamics. That article was heavily reviewed by a vehicle dynamics engineer before it went public. If anyone has a problem with it or anything I build for vehicles please express your concerns here and I'll be happy to explain the in's and out's of how and why. If you have a better idea or serious concern lets hear it!!!!!!!!!!!!!!

 

[4WheelUnderground]

For those looking for more academic information on suspension design, Carroll Smith's Tune to Win is a good starting point. Yes, most of the chassis engineering literature is about racing, but kinematics are kinematics.

Cliffs notes: Engineering often requires you to make compromises

The only problem with that kind of kinematics you speak of is that they don't take in to consideration the terrain you're on isn't level to the earth. Going up a 50* hill changes things drastically! For example, I've helped friends dial in their geometry suspension designs on various other rigs and I've always gotten their rigs to climb better with less anti squat then more. Which is a total opposite to most road course racing or drag. My only point is that dynamics change when the terrain changes. Building geometry for terrain that is never the same is not the same as consistently flat black top.

 

[4WheelUnderground]

If you guys want one of those fancy super flex radius arms for really cheap. Here is what you do. Un-bolt the forward bushing form one of your current radius arms. Done!

 

[4WheelUnderground]

Oh ya I almost forgot. Here is your Mothers Day sale. I'll going to let the first 5 FJ80 brackets sets go for $500 a pair. That's about a 35% discount. I will also discount the coilovers and bumps 10% as a package with the link arms at full price if all 5 sets go with in the month. Lets get this train rolling.

 

[jcardona1]

Wait what? What's in this kit? Panhard brackets? Coilover towers?

 

[TheBigBoy]

Wasn't going to bother. But seeing as how you asked nicely. Firstly, 4WU's post above... Clearly you don't know much about superflex radius arms. I'm not for or against them. Stock radius arm seperation is 2x 185mm to control axle wrap. Binding is at its maximum as they are on a level plain. The same seperation verticly gives the least amount of binding with a radius arm design. But they handle like crap.

Go ahead and unbolt 1 of the front radius arm bolts and take it for a drive. You will notice straight away that it dives down on unbolted side under braking. Because only 1 side of the axle wrap is now controlled. And there is a huge amount of rotational force twisting the other. I make this point because the same thing happens with a 3 link vertical separation. With the tower not centred and to 1 side. So in a perfect world the tower needs to be dead centre to control and disperse the forces equally to each side (when braking in a straight line). How ever braking when cornering, (even with a centred tower) unloads the forces from the cornering side and still happens although not as bad. This is why a parrallel 4 link with the same length links is far better for controlling this. Although binds more than the 3 link.

Back to superflex. This is why the superflex arms still have 2 vertical bushes on 1 side. Yes they are closer, but to combat that 1 of the bushes is much smaller with much less bush deflection. So it still controls axle wrap and reduces binding just enough to allow for great travel. Which is the key to great on road and great offroad capabilities.


The pics I've seen for 4WU sets ups have varied heaps. 1 of a truck with 40 or 44" tires with no where near the correct amount of link seperation from upper to lower. 25% of tire size is minimal. Realistically 33% or 1/3rd is required. Then there are things that have been done (maybe it's just to get them to fit) but add undue stress to everything. Your lower links should never dissect higher than the axle instant centre. This creates more leverage and extra stress on bushes/towers. The same with not dissecting your coil perches to axle instant centres. Meaning they need to remain neutral and sit ontop of the housing. You've taken a force that's normal taken by the housing/tires, and now turned it into a 100% rotational force. Do you know how much force there would be when getting airborn with coil overs that are stepped off to the side of the housing/ or coil overs that are mounted onto the lower link arms as I've also seen somewhere. So much unnecessary rotational force a extra stress for no reason at all.

If its a 100% trail rig, you can do what ever and it doesn't matter. But what 90% of people are looking for is great on and offroad.

 

[half k cruiser]

Perhaps Toyota 4wd magazine can run a shootout between stock, 4WU, Superflex, and Battlement arms. Maybe put it in the August issue this year. This thread has turned into a real pissing match from the OP's original post of his setup. It might be beneficial to future readers to have this information in a different thread.

 

[TheBigBoy]

It depends which hat you wear when you drive it. Different people want different set ups, for different uses. None are right or wrong.

 

[Booger weldz]

Wtf are you talking about 'bigboy' ??? You are so far on tangents of stuff you obviously have ZERO experience with. I cant even begin to describe how your discussion is dog**** and full of atypical reverb.

Build it, wheel it, talk about it. We can analyze this mathematically if you wanna get crucified in front of the worldwideweb?

 

[TheBigBoy]

Lol it's basic s*** booger. You guys think your so damn smart... I've built plenty of link suspension. Can you not understand the simple things I'm explaining here??

 

[Booger weldz]

Im not smart, im dumb. Learning from mistakes is invaluable. Youre talking nonsence and i apologize if that insults you.

Edit:this is the polite version of me telling you i can hand you youre ass mathematically or scientifically suspension wise. You choose.

Lol it's basic s*** booger. You guys think your so damn smart... I've built plenty of link suspension. Can you not understand the simple things I'm explaining here??

 

[4WheelUnderground]

Wasn't going to bother. But seeing as how you asked nicely. Firstly, the post above... Clearly you don't know much about superflex radius arms. I'm not for or against them. Stock radius arm seperation is 2x 185mm to control axle wrap. Binding is at its maximum as they are on a level plain. The same seperation verticly gives the least amount of binding with a radius arm design. But they handle like crap.

Go ahead and unbolt 1 of the front radius arm bolts and take it for a drive. You will notice straight away that it dives down on unbolted side under braking. Because only 1 side of the axle wrap is now controlled. And there is a huge amount of rotational force twisting the other. I make this point because the same thing happens with a 3 link vertical separation. With the tower not centred and to 1 side. So in a perfect world the tower needs to be dead centre to control and disperse the forces equally to each side (when braking in a straight line). How ever braking when cornering, (even with a centred tower) unloads the forces from the cornering side and still happens although not as bad. This is why a parrallel 4 link with the same length links is far better for controlling this. Although binds more than the 3 link.

Back to superflex. This is why the superflex arms still have 2 vertical bushes on 1 side. Yes they are closer, but to combat that 1 of the bushes is much smaller with much less bush deflection. So it still controls axle wrap and reduces binding just enough to allow for great travel. Which is the key to great on road and great offroad capabilities.


The pics I've seen for 4WU sets ups have varied heaps. 1 of a truck with 40 or 44" tires with no where near the correct amount of link seperation from upper to lower. 25% of tire size is minimal. Realistically 33% or 1/3rd is required. Then there are things that have been done (maybe it's just to get them to fit) but add undue stress to everything. Your lower links should never dissect higher than the axle instant centre. This creates more leverage and extra stress on bushes/towers. The same with not dissecting your coil perches to axle instant centres. Meaning they need to remain neutral and sit ontop of the housing. You've taken a force that's normal taken by the housing/tires, and now turned it into a 100% rotational force. Do you know how much force there would be when getting airborn with coil overs that are stepped off to the side of the housing/ or onto the lower link arms as I've also seen somewhere. So much unnecessary rotational force a extra stress for no reason at all.

If its a 100% trail rig, you can do what ever and it doesn't matter. But what 90% of people are looking for is great on and offroad.

The supper flex arm works with one of the four mounting locations on a shackle that swings and pivots just like any shackle you'd find on a leaf spring. Because it is pivoting and swinging it is doing nothing in terms of resisting flex. As braking purposes you would most likely find that you get some wonder from a set up that uses one removed bushing. So in that portion you are correct. But that's about it really. Truly not being a dick. But that's all you'd really notice. As for designing a suspension that uses the geometry to counter the body lean... no thank you. I don't want the geometry to force my truck to do anything nor do I want the suspension to resist movement.. I want the geometry to act as though it was not there. The last thing a suspension system should do is force the chassis to do anything other than stay perfectly still.
As far as my 4WU setup goes. You mention the 25% rule of thumb that everyone tries to use that was stereo typed from Pertersens magazine 10 years ago. And while that sounds really good in our heads, there about 1000 builds since then of people using 8" of separation and less on vehicles of various weights and power and tire size that aren't braking their stuff. A 40" tire needs 10"s of separation at the axle if we use that rule. But rarely do we see anyone use more than 9"s. Let us not forget the reason why the 25% rule was put into affect. It was for the purpose of torsional resistance. Solely! But if brackets and joints and link arms aren't braking with 8"s of separation then why would you or anyone for that matter claim that one with it is built wrong? That to me sounds like someone has an idea stuck in their head about how to build/design their suspension and cant grasp what is really going on. And because Im a small time guy not a big fat magazine I cant be trusted. Do you truly believe that 33% is needed. So we should all start building our stuff with 12.5"s of separation. REALLY???
Lower links higher than center line of axle. Do they put more stress on components?: 100% yes they do. In the case of my design about 20%. Have any of you wondered why my stuff still works better then anyone else's. It rock crawls better. Drives better on the street and Baja's better. The brackets and links and bushings and even the bolts I choose are all selected to handle that extra abuse. no other part of the truck sees this extra abuse, just the suspension. But I've designed for it. So why does it matter then you or anyone else. I'll include that coilover mounts in there too. Build the stuff stoutly! The argument of extra torque on the system is so over thinking the point of geometry. Geometry IS handling. Bracket design is for strength. I have both!!! yes I know exactly how much force there is when getting air born. And its no more then I've accounted for.
As for putting the upper link in the center of the axle tube. You are correct putting it off to one side or the other will play on caster during articulation and have braking effects on the vehicle. But if you put in the middle of the tube then you cant fit it on the vehicle because you have an oil pan, with out having the lower links far below the axle tube and making a huge rock anchor and or REQUIREING extremely low lift highs to get your links flat for PROPER handling. There are certain compromises we all have to live with when building around an existing platform.
I understand that my designs are not for everyone. But I don’t put stuff to market that are flawed as you claim. It sounds to me your understanding of geometry and engineering are suffering. By the way my father is an engineer. Don’t think I havent picked up on a few things in the 37 years I’ve been on this earth.
Yes I am here to make a point. If you think my stuff is weak its because you don’t like what I do. It’s not because your argument holds water.
When I first started doing this, people told me that my stuff wont work because the link is about the axle and it does nothing to protect the drive shaft. If that were true then everyone with leaf springs on top of the axle would be screwed. And IF it had further problems you would have seen them by now. I don’t go around paying people off to keep quiet when something goes wrong. NOTHING has gone wrong.
You are entitled to your own opinions.
But if you have no proof to back them up, then keep them to yourself. You are just poisoning knowledge and the forum from good tech and filling it with age old beliefs that are unwarranted like old wives tales. These days we know better than we used to. So let the tech flow!

 

[TheBigBoy]

I'm not talking nonsense at all. Maybe it's just a communication failure. Try to understand it before shooting it down.

 

[4WheelUnderground]

Lol it's basic s*** booger. You guys think your so damn smart... I've built plenty of link suspension. Can you not understand the simple things I'm explaining here??

There is a difference between understanding what you are saying and it actually being an issue. Im not saying its not true just that your concerns are overly stated. They are not something to worry about. I’ve already done that and taken care of it.

 

[TheBigBoy]

Run it through a stress analysis and see the extra stress yourself. I know you've raised it higher than the axle centre to get better numbers. But really it should be done by lowering/lengthening it at the chassi.

 

[4WheelUnderground]

That is to say I understand your concerns. They are not with out warrant. But I took them into consideration when I designed this stuff.

 

[TheBigBoy]

So everything I've mentioned you have tested and has valour?

I know you can't fit a centre tower. My point was, that 4 link (all though more restrictive) is better in design as its symmetrical and distributes it evenly.