Synergy Suspension 4 link Or Rock Krawler 3 link whats better?

[redrider2911]

Screw numbers.

My 2" x .25 DOM lowers, all 4, look like bananas.

My 1.5" x .25 tie rod looks like a banana.

But I guess the little hex stock will be OK, as long your link mounts are below the axle centerline. Mine aren't, which is probably a contributing factor.

Are you still going on about that post 5 days ago? You know that from below center line of the axle to above does make a difference. Thats simple physics.



Link to a simple calculators for everyone

http://www.engineersedge.com/section_properties_menu.shtml

1.25 hex: .23438
1.25 x .75: .1666
1.5 x 1.0: .26542
1.75 x 1.25: .3885
2.0 x 1.5 (synergry): .53594
2" solid (rock Krawler) .784

not too bad. I dont know If your working on different #s or what..

Now lets talk about. Yield strength. People dont want their arms looking like bananas right?

1018, what MOST companies use
http://www.pmtsco.com/1018CD.HTM
tensile strength, 64000 PSI. Yield strength, 54000 PSI

12L14, What I use
http://www.pmtsco.com/12L14CD.HTMtensile strength, 78000 PSI. Yield strength, 60,000 PSI

Back where I used to work as an engineer we would use 1-1/4 hex for gear shafts. They dont come perfectly strait of course like anything. We would take the 4 foot long shafts under our 4 ton press to straiten them to tolerance. In order to take a .003 bow out of this material you would have to bend it atleast 8 inches in the opposite direction.

So are you saying I am completely wrong on my math and material choice?

 

[RCman]

So are you saying I am completely wrong on {snip} material choice?

Material choice? Yes.

Simply posting section modulus numbers does nothing for the average user. Your calculated numbers match my hand done math, so thank you for pointing that out.

Even at 60000 psi (only ~6.3k difference from 1018, not a large difference) You are only gaining 106.7lbs at the point load force. You total then becomes 1026.6lbs, which is STILL LESS than 1.5" X 0.250 wall tubing.

Also, how many of your customers land on the edge at every time?

I'm not here to start a war, just simply pointing out the facts. Your link material choice is inferior to the conventional 1.75" or 2" sizes. End of story.

 

[vetteboy]

Are you still going on about that post 5 days ago? You know that from below center line of the axle to above does make a difference. Thats simple physics.

"A difference."

Yes, we agree on that.

The magnitude of said difference, or even what that difference is? Not so much. I'd be happy to take it back to that other thread if you'd rather.

Back where I used to work as an engineer we would use 1-1/4 hex for gear shafts. They dont come perfectly strait of course like anything. We would take the 4 foot long shafts under our 4 ton press to straiten them to tolerance. In order to take a .003 bow out of this material you would have to bend it atleast 8 inches in the opposite direction.

This I gotta think about...

So your argument is not that the material is strong enough to resist bending...it's that it's resilient enough that it doesn't matter? Kinda like those aluminum flexy tie rods?

 

[asp]

Now lets talk about. Yield strength. People dont want their arms looking like bananas right?

Back where I used to work as an engineer we would use 1-1/4 hex for gear shafts. They dont come perfectly strait of course like anything. We would take the 4 foot long shafts under our 4 ton press to straiten them to tolerance. In order to take a .003 bow out of this material you would have to bend it atleast 8 inches in the opposite direction.

So are you saying I am completely wrong on my math and material choice?

No, they don't.

Did you guys have a granite table that you measured that 0.003 bow with? That's pretty small.

8" is a lot of deflection. Cool that it only plastically deformed by 0.003. But who the hell wants their link bending 8" when they land on a rock, even if it returns to straight when the force is relieved? I'd run the other way if I saw that happen on a trail.

I think material choice, as long as it's a high grade of steel is nearly irrelevant. The modulous of elasticity of steel varies less than 10% from the stiffest to the least stiff grades of steel - it's the yield and uts that vary signficantly. They're all pretty close and worst case scenario, within reason, should always be assumed during any calculations. I don't want my link plastically deforming at all, and I'd really prefer if they elastically deformed as little as possible too. More than 1/16" I think would be undesireable.

8" of flex would cause a 48" bar to have an effective length of approximately 45.5" - a whole 2.5" shorter. When running a more complex or longer travel suspension setup, a bowed link will cause the suspension geometry to shift and could even cause a coil over or air shock to hit the side of its mount. Just thinking about the potential problems that 8" of link flex causes. (Link flex... is that a new term that I just coined?)

Also, the 'landing on the edge' or on the flat is crap. Plan on them landing on the flat, because at some point, it will happen.

 

[redrider2911]

No, they don't.

Did you guys have a granite table that you measured that 0.003 bow with? That's pretty small.

Yes. I big granite table, some feeler gauges, and sometimes a dial indicator. Like I said these were gear shafts and had to be as true as we could get them.

8" is a lot of deflection. Cool that it only plastically deformed by 0.003. But who the hell wants their link bending 8" when they land on a rock, even if it returns to straight when the force is relieved? I'd run the other way if I saw that happen on a trail.

I was using this application as an example of what kind of forces my links will take and still not actually fail. Have you ever seen a link ripped apart? or broken in half? No. You see DOM kinked or bowed or all beat up with dents in them. Once the DOM has been deformed to this point the structual integrity has been compromised. Not to mention your link geometry all messed up from the deformation.

I think material choice, as long as it's a high grade of steel is nearly irrelevant. The modulous of elasticity of steel varies less than 10% from the stiffest to the least stiff grades of steel - it's the yield and uts that vary signficantly. They're all pretty close and worst case scenario, within reason, should always be assumed during any calculations. I don't want my link plastically deforming at all, and I'd really prefer if they elastically deformed as little as possible too. More than 1/16" I think would be undesireable.

I just dont think you can "have your cake and eat it too". (cost effectively) Either your material is really hard but brittle. Or decently hard (hard enough for the application) but also elastic.

Also, the 'landing on the edge' or on the flat is crap. Plan on them landing on the flat, because at some point, it will happen.

Agreed. Just bringing it up while in the topic.

I've also seen much larger joints wear out unreasonably fast in suspensions, so there's no way I'd ever trust that size.
It's hard to argue with results.

I have also seen this. But why spend 4 times as much on a heim that you will have to replace in 18 months, or however long yours last for your application. You can buy a heim that is a little smaller, be PLENTY strong, cost 4 times less, and will last almost just as long. Dollars/running time is much more efficient.

 

[MoparManiac]

So since redrider completely IGNORED RCMan and vetteboy's actual FACTs...

I'd recommend going with Poly Performance's kit. Their kit seems well engineered and plenty strong enough.



Man, where's the popcorn smiley?

 

[redrider2911]

So since redrider completely IGNORED RCMan and vetteboy's actual FACTs...

I'd recommend going with Poly Performance's kit. Their kit seems well engineered and plenty strong enough.

I didnt ignore any facts... Did you read everything? I just stated that there were more facts to be taken into consideration.

I havent had a single customer complain about link strength or them bending or breaking. Granted I am still a small company but only more time and more good reviews will show a wider span of consistent results.

 

[asp]

Yes. I big granite table, some feeler gauges, and sometimes a dial indicator. Like I said these were gear shafts and had to be as true as we could get them.

I was using this application as an example of what kind of forces my links will take and still not actually fail. Have you ever seen a link ripped apart? or broken in half? No. You see DOM kinked or bowed or all beat up with dents in them. Once the DOM has been deformed to this point the structual integrity has been compromised. Not to mention your link geometry all messed up from the deformation.

Gear shafts would need to be quite straight, I very much agree.

Links don't really catastrophically fail, I'm with you there. And I agree that when DOM or square tubing gets kinked it's structural integrity is compromised and needs to be replaced.

The metal in your links may not be failing as far as the state of the metal, but they would fail to serve the function of a suspension link if they're bending even just an inch. Even if they bend a half inch within the fully elastic region of deformation, that's too much. If your links are flexing, they're not doing their job. What would you think if you saw a link elastically bowing over a rock about 2-3"?

caveat: factory links do twist a little bit, but they were designed for a very different purpose

I'd like to point out that you stated that there were more facts to be considered, but dismissed the ones they presented.

To the op: Man, I'm really sorry we derailed your thread so hard.

 

[vetteboy]

I was using this application as an example of what kind of forces my links will take and still not actually fail. Have you ever seen a link ripped apart? or broken in half? No. You see DOM kinked or bowed or all beat up with dents in them. Once the DOM has been deformed to this point the structual integrity has been compromised. Not to mention your link geometry all messed up from the deformation.

I finally changed it out at this point:

Yes, that's two broken johnny joints with bent shanks and a broken 9/16" through bolt there too. I guess that also makes me wonder about the 3/16" wall thickness above the threads on the hex stock...with a direct bending hit like what happened on mine, do you think there's any possibility of failure there?

Wouldn't say my link geometry was all messed up though.

I don't think this thread is derailed...it's good discussion on the merits of different kits. Food for thought.

 

[ktm racer 419]

7/8" heims for the lowers wouldnt make me happy.

im sure you can throw some numbers at me justifying why you use them, and that they are plenty strong.

but they are dainty compared to what everyone else uses for thier lower arms. and i don't do dainty if i can avoid it.

 

[ktm racer 419]

Not to mention your link geometry all messed up from the deformation.

how much will link geometry be messed up from a lower control arm being slightly bowed anyway? I mean if anything, all it does is bring the mounting points maybe 1/8" closer (and thats being generous)

ZOMG YOU SLIGHTLY BENT YO CONTROL ARM YO ANTISQUATS ARE AT A BILLIONDY PERCENTS!!1!1!!1

 

[kastein]

I don't worry about a bent control arm screwing with link geometry... well, folded up stock uppers do, but real control arms don't bend that much.

I worry about them being weakened and turning into pretzels the next time they get hammered on. Once there is ANY deflection, it becomes far easier to bend the arm more, nevermind work hardening effects.

 

[ktm racer 419]

if you have a link deformed enough to significantly screw up your geometry, im pretty sure you have bigger issues to worry about.

 

[srimes]

redrider: can you stick a jack in the middle of a link and post a pic? Then we can see how much it deforms and speculate less.

 

[ktm racer 419]

redrider: can you stick a jack in the middle of a link and post a pic? Then we can see how much it deforms and speculate less.

that "test" would mean nothing to me

a suspension link landing on a rock is a different kind of stress than slowly jacking up from a suspension link

 

[redrider2911]

that "test" would mean nothing to me

a suspension link landing on a rock is a different kind of stress than slowly jacking up from a suspension link

I wish I had video. Still need to build my next jeep. You'll have to wait till spring so I can jump up onto some rocks at naches on purpose and Ill get some good quality video for you guys.

 

[98stocker]

I think the kinds of hits my lower arms take from rocks is similar to laying the arm on the concrete and hitting it with a sledgehammer a whole bunch of times. I think my lower arms (2 inch, .25 wall) would dent and begin to bend. But I don't see how I could significantly damage solid hex material.

Sure the overall strength of my arms may be greater, but the resistance to damage in my uneducated mind might go to the hex.

 

[kastein]

It's honestly more like placing a piece of stock on top of two widely spaced cement blocks and hitting it with a hammer at the middle. Less outright compression force and more bending (compression on one side, tension on the other.)

 

[ktm racer 419]

I wish I had video. Still need to build my next jeep. You'll have to wait till spring so I can jump up onto some rocks at naches on purpose and Ill get some good quality video for you guys.

SWEET! I like seeing people try to break stuff on purpose.

still interested in what ya hafta say about the other queries though.

 

[XJLI]

if you build a set for ktmracer and he cant break it, i'll pay for it. twice.