Link mount location on axle housing

[Hollowpoint]

I just got a pre built 9" with the link mounts on the front of the axle, and the top link mounts higher than any I've seen before.

What do you guys have to say about the higher strength of the link mounts on top and bottom, compared to the higher clearance of a fwd mounted lower mount?

2nd thing is whether the top link mounts should be lowered like Newline's setup, therefore elongating the roll center. Either way, I know I have to gusset that thing.

Here's a pic of Newline's kit, as well as my rearend as it sits now.

[Hollowpoint]

Alright, my pic supposedly "contains no data." So here's the link to the URL of my setup as I got it.

http://i7.photobucket.com/albums/y268/rattpoison82/773ad24b.jpg

[Justin]

Who did you get the set up from?

[matt_helton]

those upper link mounts need alot more plating or they will break off.

do a search for "lower links 101" pages and pages of info.

[matt_helton]

oh yeah, and those welds look questionable at best. and there needs to be more thickness in the plates where the heim bolts will go through.

[Justin]

Why did somebody hack up the work newline did on that housing?

[Hollowpoint]

It's a Curry assembled housing, with the upper link mounts redone by the last owner. I bought it off the classifieds.

I already intend to put some work into this, just deciding on the lower link mount location.

The search provided 0 results for lower links 101 in various word combinations.. just spent the last 2 hours reading through search results with none talking about link mount location on the housing. Informative search, nonetheless.

[matt_helton]

ok, well im no "genius" engineer type like alot of guys here but ill give my 2 cents anyhow. just speaking in a logical manner, it makes it alot easier on all the components involved when the lower link tabs are under the axle tubes rather than infront. yes it gives more ground clearance but stresses the parts more. all the load of the truck is being carried by the lower links....if the tabs are under the axle the load should be a staight downward pull for the most part. if they are infront of the tubes the load would also push straight down but would intern want to twist the axle forward alot, which would load the hell out of the upper links and heims causing premature heim/bushing failure as well as stressing all the mounts more.

i would build lower link mounts off the front only if i was making a 4-tube link set up with the coilover off the axle in a near 1-1 ratio. because then the load is actually carried by the housing and not the lower links/mounts. they are just there to locate the axle housing.

[matt_helton]

ill let more qualified people talk on the upper link height but i think taller is better somewhat. lol

heres a housing my friend Tony who works at Currie built for their race truck. its in an F-150.

[matt_helton]

oops, forgot this one....

[Chris_Wilson]

I'd put the lower mount under the housing tube. The ones on my 8 truck are in front
and it puts huge stress on the upper links. I've been reinforcing the upper link mounts
after each race, chasing cracks and adding structure to the mounts. Last race both
upper links bent the Bowman 3/4" bolts. I'd rather give up some ground clearance.

[ChuckH]

You also have to think about the location of the links where their mounted to the frame, this i the area i would stay in with mounts, mount the top axle links centered above, the bottom links centered below or maybe 1/2 - 1 inch forward ( but below approx 1.5 inches from the tube) the top 2 links that mount to the frame should be mounted so they are behind approx 6-7 inches ( or think of them being 7 inches shorter than the lower links) in relation to the mounting location of the lower links.

[Outcast]

I would agree that mounting the lower tab below the axle tube is better in terms of stress, for all situations. Even with shocks/springs mounted on the axle itself, you still must consider the torque reaction in the axle housing and how that is transmitted through the links and their subsequent mounting points on into the chassis.

Mounting the lower tabs on the front of the housing does achieve increased ground clearance. But to what avail when your differential already hangs down below the axle centerline any way? Also you pay the price that others have already mentioned by creating additional twisting forces on the housing and additional loading on the upper links. Having the shocks/springs on the axles reduces this stress but it is still there due to the torque reaction in the axle housing itself. Also, mounting the links in front of the housing will typically reduce the amount of anti-squat the rear suspension generates. Now that, in itself, is not necessarilly a bad thing but should be considered none the less.

I would agree with the consensus that the tabs should be mounted below the axle tube. Whether or not you want to keep them directly below the center or move them forward is up to you. Again, this will change the antisquat some and also effect the pinion angle change as the suspension cycles. I believe that controling the pinion angle thoughout the travel is the biggest reason those lower mounts are moved a little forward. However, by doing this, in conjunction with shocks springs mounted lower arms, you start placing a moment back on the housing and adding stress back in so consider that too.

I would also agree with the idea that for a rear suspension, the top links need to be a little shorter though no less than 60% of the length of the lower links if it can be helped.

As to the height of the upper mounts on the axles. Basically that will change your roll center height, and again your anti-squat and pinion angle change so bare those in mind. Also consider chassis clearance and the fact that making higher mounts means additional boxing and additional unsprung weight. Most likely, the logic behind a higher set of upper mounts is raise roll center height. I would also understand a higher set of upper mounts in conjunction with the lower mounts being on the front of the axle tube because that would reduce the force put on the upper links.

Just food for thought, there is no real "right" way to do this stuff.

[Hollowpoint]

Thanks for all the input, guys. Explains exactly what I was looking for. Outcast: I can't agree more with that quote.

[Outcast]

Thanks for the kind words.

[ChuckH]

I would also agree with the idea that for a rear suspension, the top links need to be a little shorter though no less than 60% of the length of the lower links if it can be helped.


60% would be way to short for a good design, the minimum would be more like 85% - 90 % to stay close to ideal, i wouldn't ever go below 80 % if your pulling much travel, having said that lots of things that are not ideal can still work, he11 look at the front Sup of some ford trucks ;) :D

[Outcast]

Actually, that was a typo. I meant to say 70% as a minimum. I would agree that it depends on how much travel you're going for but I'm not a big fan of mega travel in the first place.

[Ramsey_ElWardani]

but I'm not a big fan of mega travel in the first place.Nor is Nye Frank; what is your conection to him?

[Outcast]

Just a fan/student of his work, going back to his drag racing days. I love what he does and how he thinks. I really got into his work while laying out a front suspension for another "severe duty" application a few years ago. It incorporates a few things, from a geometry perspective, and after sharing my thoughts with a well known builder he said, "That sounds alot like the kind of stuff Nye Frank does." It was neat to find out that someone out there thinks about things in a similar fashion so I've tried to follow what he does/has done ever since. Hope to meet him or get the chance to talk to him someday.

[Stephen]

Chris Wilson: did your upper link bolts bend from compression on the links or tension? It sounds like you have a good idea what's causing your problem but if the bolts are bent from tension forces, it's from torque (drive torque), not link forces from supporting the truck's weight.

In general, the key to keeping link forces down is vertical separation on the axle housing between upper and lower links. Again, it's not the answer to everything but I should mention the link geometry program floating around, check CK5 or Pirate for the latest version, it's interesting to play with.

Who built fabtech's prerunner with the lower arm mounted on top of the axle tube?

[Chris_Wilson]

> did your upper link bolts bend from compression on the links or tension?

I can't be sure. I could not tell they were bent until I tried to remove them.
By the time I realized they were bent, I had already started spinning them out with the impact. It's the bolts at the front that bent. At the rear end, the upper
link mounts also started to tear away from the housing. So the primary stress
is tension. I think I've solved the rear end mounts with some additional trussing
and triangulation. And we added some more structure to the front mounts too.
It's not like it's ever actually failed. In fact I've never failed to finish a Baja race.
It's just that when I do my down-to-the-bare-frame race prep, I always find signs
of too much stress and ways to improve it for the next race. It's all really a lot
stronger now. I replaced all the heims since they were under so much stress thinking
that any heim that could bend a 3/4" Bowman bolt may have been overstressed.
And I'm mag'ing the upper links even though there is no signs of any stess on those.
It's really hard to keep a class 8 truck together. Everything is so powerful and heavy.

[Stephen]

> It's really hard to keep a class 8 truck together. Everything is so powerful and heavy.
And lots of it has to be in the wrong place too. I think that's some of the appeal.

How much vertical link separation is everyone running?

[GOAT1]

Chris Wilson: did your upper link bolts bend from compression on the links or tension? It sounds like you have a good idea what's causing your problem but if the bolts are bent from tension forces, it's from torque (drive torque), not link forces from supporting the truck's weight.

In general, the key to keeping link forces down is vertical separation on the axle housing between upper and lower links. Again, it's not the answer to everything but I should mention the link geometry program floating around, check CK5 or Pirate for the latest version, it's interesting to play with.

Who built fabtech's prerunner with the lower arm mounted on top of the axle tube?

Brian Kudela of Light Racing designed parts of that truck, at least the rear suspension, Matt Goodsell started building it and I think Hussman finished it. Kudela and his team are about the only ones that apply any engineering to off-road race cars and actually know why and how things work. If you look at most of the trucks he has designed, (Baldwin's TT and Big Mac) the lower link mounts are at the center or higher than the axle centerline. They also incorporate higher upper link mounts to get the roll center higher. Most of his designs also use a rocker arm shock set up with either torsion bars or coil over shocks in the case of Fabtechs prerunner so the links do not carry any of the shock or spring forces. Some of the trucks that Kudela has designed with the shocks and springs mounted on the lower control arms are Honeycutt's Tundra and the last Little Mac, but I dont know where the lower control arms are mounted on the axle, I will have to dig up some pictures.

[Big_Matt]

From the Tundra class 8

[Stephen]

From what I know of Kudela and light racing, this is stuff we should pay attention to. They seem to have good reasons to do what they do.
Looks like a LOT of vertical separation, 10"?

[Hollowpoint]

I'd be really interested in where the upper links' fwd mounts are. The setup on my rearend that I wanted to tear off rightaway, doesn't look that far off from this setup(Kuderla's).

[Outcast]

Bare in mind that photo shows the lower fourlink axle mounts are actually above the axle centerline. Thus some of the loading both in terms of torque reaction and vehicle weight is taken off of the upper bars in that setup versus one where the lower fourlinks mount right at the axle centerline.

[Hollowpoint]

Does anybody know what is achieved by placing both mount locations above centerline? As opposed to top/bottom, and in top/in front? From what I'm gathering in this thread, placing the mount in front is the worst place to mount the lower links, strength wise.

[ChuckH]

Strength wise there all relatively close, thats not why their mounted where they are, different mounting locations effects how the rearend works under braking and acceleration.

[Josh_K]

All this random speculation is quite funny.

Chuck and Chris excluded thou.

Josh

[Hollowpoint]

I'd rather make a guess than sit on my *** till someone hands me the answer in gift wrapping.

[partybarge_pilot]

Who's Guessing? It's pretty cut and dried dynamics.

[Josh_K]

I am sorry if I am too course and blunt for some. I don’t mean to insult. But some times the solution is so simple that it’s comical to read the debate.

P.B. is right. It’s simple. I think once again people are getting rock crawling issues confused with off road racing. They to totally different parameters and I know you cant make one chassis excel in both fields.

It has been my experience that the ground clearance issue isn’t that important in off road racing. Things do hit my lower arms (flying rocks off the front tires) and hard too but build them strong and it doesn’t matter. Furthermore, mounting the links in front of the axel makes for a weak link mount on the axel. Just think about the wreck that can be caused by the axel breaking loose on one side a turning the truck at a high speed.

I think Ramsey and Chris have seen a truck that it’s happened to too (Kurt Kupik). It isn’t pretty.

Oh ya, the force that is putting a huge tension loads on the upper links inst inducing “anti squat” it’s inducing “squat”. On a comp crawler the ideal situation is neutral squat and on an off road race truck / fast prerunner you want to induce squat. The amounts thou are strictly personal opinion and feel.

Josh

[Outcast]

Just because the upper links are put in tension, doesn't mean that squat is being produced instead of anti-squat. Anti-squat and squat as well as Anti-dive and dive are a function of how the torque reaction of the driveline and braking systems are input back into the chassis via the instant center resulting from the suspension geometry. You can produce anti-squat with the lower links above, right at, and above (Edit: that should be below) the axle centerline. It depends on the overall geometry of the suspension. That is not speculation, that is what I was taught while obtaining my Engineering degree.

Having the lower links above or at the axle centerline has to do with other factors that said designer gave priority. In my opinion, which is based on my own observations and not speculation, those factors, mainly ground clearance, are not worth the additional loading placed on the axle housing, links, and mounts for an Off-Road Racing application. Those setups do make more since for Rock Crawling applications but consider what those vehicles do in contrast to Off-Road Racing vehicles. Also consider the fact that those vehicles (at least the purpose built crawlers) are much, much lighter so the overall loading is not as great.

[Josh_K]

To quote Outcast.

"That is not speculation, that is what I was taught while obtaining my Engineering degree."

Hoo boy... Here we go with the engineers...

[matt_helton]

hahaha, oh man Josh. just let it go. its a no win situation.

[Outcast]

Hey take or leave it, you weren't the one asking the question in the first place. To disagree is fine, and if so, state why you do because I'm always willing to learn. But don't jump into a thread and assume someone's of view is merely speculation. I was just clearifing that my points were rooted much deeper than that. I don't see how me or anyone else defending ourselves against your ad-hock statements deserves a 'hoo boy'.

[Hollowpoint]

Rediculous... this thread needs to be killed. Ironically, I posted this question on this site hoping to avoid this nonsense. That's great, good job there.

[CRAIGHALL]

Plain fact no speculation here. Baldwins trucks have a 10" center line from lowers to upper uniball,with lowers at axle centerline.

[partybarge_pilot]

Plain fact no speculation here. Baldwins trucks have a 10" center line from lowers to upper uniball,with lowers at axle centerline.


Yes, but they are cantalever. Bottom arms only locate. It would be a whole defferent animal if you were supporting the truck with them.

[FABRICATOR]

Are we talking about these? One picture is worth a thousand speculations...http://www.race-dezert.com/forum/attachment.php?attachmentid=999&d=1031891669

[matt_helton]

i coulda sworn were talking about rear suspension here..........

[Stephen]

Hmm, let's think about this one a little bit (or dare I say apply some math to the problem?)....
IF
we smack the rearend with 10,000# of vertical force (just a kiester number for reference) and the lower link is mounted dead in front of the tube and about 4" from center (1.5" for tube radius and 2.5" for link spacing, and again a general guess), and we have a upper link arm mounted 10" above the lower

THEN
we create a 4000# compressive stress on the upper link arm. Assuming we use a rod end that's rated for 50K# or more, that big bump doesn't even phase the end. Especially considering that it's compressive and it's tough to damage or even stress a joint in compression.

Based on this I'd build the lower link mounting point where ever you want based on factors other than the stress induced by bump loads on the upper link arm. Maybe you could do something smart like use that leeway with the mount point to control the roll axis or give you more link separation if you're upper brackets are close to the housing.

[partybarge_pilot]

It's not the rod end thats going to suffer, go take a 1.5X.120 wall tube 3' long and stick it in your press. Tell Me what happens when you reach 4K. Not to mention any aditional side loads that may be imparted.

[partybarge_pilot]

Haha, I'm an idoit. Just out of curiosity I calced out how much load it would take.... In a perfect world it would have a compresive strenght of about 11.5k....... Which makes Me wonder why they bend so easy when you roll?

[Outcast]

Well, 1) Since the upper links are usually converging, they are not loaded in simple compression along their axis. They are also loaded in bending. 2) During rollovers often times, the entire weight and subsequent momentum of the vehicle touches down on one tire so that side of the suspension takes all the hit. Food for thought.

I would agree that a properly sized heim can take just about any abuse but lets also consider the compression and beam strength of the links and also the strength of the mounts too.

The Taylor truck is awesome, period. Having seen the craftsmanship put into it and the truck's performance I can certainly appreciate it and it's sophistication. Now having said that, I would not set up the axle with the mounts like that. Does it work for them? Obviously and yes its easier to get away with that kind of setup when the lower links are not weight bearing. But in my own personal opinion I would not risk the potiential problems with the additional loading on the rearend and suspension pieces that still exist due to the torque reaction that occurs in the axle housing itself. The Trophy Truck class is still very much a war of attrition so reliability is still a big factor in determining winners, thus the reasoning for my opinion on this subject.

Yes you can put those lower links just about anywhere you want. Just please be aware of the effects involved with various placements.

[FABRICATOR]

i coulda sworn were talking about rear suspension here..........
Oops, wrong picture...I'll look for one of the other end later.
As far as ulltimate vertical loading, this is what bump stops are for.

[ChuckH]

Well, 1) Since the upper links are usually converging, they are not loaded in simple compression along their axis. They are also loaded in bending.

uhhhhh..... with hiems on the ends of a rod-tube bending loads are almost nothing until you get to the ultimate compressive force to fail the rod-tube.

A rode-tube with hiems on both ends reacts-works the same if its converging or parallel to the frame, its in compression or tension, nothing else.

Are you going to say thats not what you meant to say !!. like with the upper arm length that you said should be 60%.

[GOAT1]

Haha, I'm an idoit. Just out of curiosity I calced out how much load it would take.... In a perfect world it would have a compresive strenght of about 11.5k....... Which makes Me wonder why they bend so easy when you roll?

That seems like a pretty low number, how did come up with that?

[Outcast]

Are you going to say thats not what you meant to say !!. like with the upper arm length that you said should be 60%.Right, you've neeever had a typo, okay.

No, I'm going to disagree. Uhhh, if the converging links aren't loaded in bending then what keeps the axle located laterally? It's not all tension/compression. Unless the link is placed in the direct alignment with the load path (I.E. Panhard rod) it will have combined loading and thus be placed under bending stress. Also, don't think in just one or two planes. Consider loads induced by articulation and engine torque.

http://images5.theimagehosting.com/Link Load.1.jpg

[GOAT1]

Right, you've neeever had a typo, okay.

No, I'm going to disagree. Uhhh, if the converging links aren't loaded in bending then what keeps the axle located laterally? It's not all tension/compression. Unless the link is placed in the direct alignment with the load path (I.E. Panhard rod) it will have combined loading and thus be placed under bending stress. Also, don't think in just one or two planes. Consider loads induced by articulation and engine torque.

http://img14.imgspot.com/u/05/243/13/LinkLoad.jpg

If the link has rod ends on each end, there can be no moments acting on it to load it in bending until one of th rod ends bind. It's all tension/compression., its triangulated.

[Outcast]

I see what you're saying but freedom of motion in the rod end does not mean that the bending loading does not exist. Yes those rod ends would allow that link to swing if nothing else was there but the triangulation of the suspension doesn't allow that. Thus the link sees bending loads.

If that is not the case, where's that other component of the lateral load then? If someone really wants to do the press test, put a heimed rod in a press at the lateral angle it would be in a suspension. Bolt the ends down to restrict them just like in the suspension and see if it takes the compressive yield force to bend that link. It won't.

[J.JOHNSON]

Is that a momomonster truck tire I see in the drawing. I'm not making fun just trying to lighten the mood.

[Outcast]

Is that a momomonster truck tire I see in the drawing. I'm not making fun just trying to lighten the mood.

Yes, the drawing is borrowed from an MT application. Excuse the crudeness but I removed most of the details to faciliate quick illustration of my point.

[ChuckH]

If the link has rod ends on each end, there can be no moments acting on it to load it in bending until one of th rod ends bind. It's all tension/compression., its triangulated.

Thank you, ding ding ding we have a winner


Outcast, this is as basic as it can get, put two hiems on the end of a shaft and it can ONLY work in compression or tension, franky i find it scary that engineers are coming out of school whom seemingly lack very basic reasoning ability's.

[Outcast]

franky i find it scary that engineers are coming out of school whom seemingly lack very basic reasoning ability's.

Speaking of basic, tell me, genius, what's going to happen to this link? Why don't you dazzle us and interpret the load paths?

http://images5.theimagehosting.com/Link Press.jpg

[Josh_K]

Chuck, what the hell do you know???

Just because you are a rock star in the off road racing world, doesn’t that mean you know how to drive a class 1 car? Do you know how to prep you class one car? Do you fix your car and change tires on it when you get flats during a race one in remote spots???? Do you make love to that car between ever race to make sure that it’s good to go for the next battle. Do you know every detail of it and how it works and why? What makes you think you know more about off road racecars than an engineer that may not have even seen a desert 1 car or 8 truck in person?

YOU ARE INCREDIBAL!!! I can’t believe the gall you have. Picking on a well-educated engineer.

I hope you relize I am being factious.

Josh

[Josh_K]

Speaking of basic, tell me, genius, what's going to happen to this link? Why don't you dazzle us and interpret the load paths?

http://images5.theimagehosting.com/Link Press.jpg

That looks like a pan-hard bar and we dont use those in the desert becouse thay suck!

Josh

[Outcast]

That looks like a pan-hard bar and we dont use those in the desert becouse thay suck!

.....And the point blows right on by Josh..... No, it's not a panhard bar. It's a link mounted in a press, thus movement only occurs in the direction of the press.

[matt_helton]

oh man, now its getting rediculous.......josh we need to get you a spelling/grammar checker program if nothing else.......:)

[ChuckH]

Dalton 8

hahaha :D

[matt_helton]

Speaking of basic, tell me, genius, what's going to happen to this link? Why don't you dazzle us and interpret the load paths?

http://images5.theimagehosting.com/Link Press.jpg

im no genius, but i suspect the mounting tabs would fail before the link would. right? the tube would be in direct compression, and the tabs would be subjected to crazy sheer forces....

[Outcast]

Assume the link itself is the weakest point...

[Hollowpoint]

Whoah... all I gotta say is WHOAH. Are we back in high school, now? Cuz I haven't heard an attempt at ridicule backfire that badly since then. Talk about statements that expose a little too much about the author. Don't get me wrong, I know sarcasm, and the reasoning for it.

About the whole nonsense of cut and dried dynamics, and this whole thing being a black and white subject of right and wrong. I've heard a lot of discussion from high end fabricators vouching for each design. That's just what I wanted to gather here, as well, not a "I'm right, cuz I say it is, and everybody else is wrong" BS. I'll go to the other site if I wanted that. I doubt anybody would go to Kudela, Nestor, or anybody else's face and give them this cut and dried talk to steer them in their holy "right direction." Within this thread itself, there's people who say NOTHING but lower links on bottom, and then suddenly, Kudela's design is shown, and then suddenly EVERY position is okay, strength wise. Leave the egos at home, add to productive discussion, leave the high school BS to the kids, or shut up. Seriously...

[matt_helton]

Assume the link itself is the weakest point...


sure, the link would eventually fail by blowing out one side or another but its still direct compression because the ends are hinged, right? this seems so simple...what am i missing here?

and i do kinda miss high school.......but only for the chicks. :)

[Josh_K]

Duurrrrr,

I just drivem mannn

[matt_helton]

which one is "the other site?"

[ChuckH]

sure, the link would eventually fail by blowing out one side or another but its still direct compression because the ends are hinged, right? this seems so simple...what am i missing here?

and i do kinda miss high school.......but only for the chicks. :)

I agree with the chicks thing, oh yeah and the other part

Hay maybe this guy is really a physicist and has discovered that the hidden so-called "dark matter" exists in a way not expected and exerts a force on the side of everything.

[Josh_K]

Sub-atomic "string theory"

B.T.W. Mr. OUTCAST,
When talking about shocks, is the correct terminology to dampen or dampening??

[GOAT1]

Outcast, that link in the press will be in tension or compression only. If loaded in compression it will not fail from compressive stresses, it will fail from buckling which technically will be from bending stresses from an eccentric bending moment from it's own deflection, but there is no bending moment applied to that link from the rod ends.

[toddz]

Outcast, that link in the press will be in tension or compression only. If loaded in compression it will not fail from compressive stresses, it will fail from buckling which technically will be from bending stresses from an eccentric bending moment from it's own deflection, but there is no bending moment applied to that link from the rod ends.

I'd agree with that - Euhler's rules for column buckling, as I recall. 'Course it's been a few years since I've been in engineering school.

Todd Z.

[partybarge_pilot]

Sub-atomic "string theory"

B.T.W. Mr. OUTCAST,
When talking about shocks, is the correct terminology to dampen or dampening??


OK, I was just down at the beach doing some research on this.

String bikinis have a definante effect on load beaing members. This can only be "dampened" by the not so rare Michigan land whale.

[Outcast]

http://www.piorek.net/pub/_me15web/9_buckling/text_9-1.htm

Euhler's formula applies to axial loading only. However, if the load, or force, applied is not directly along the axis of the beam, then only part of the total load is scene as axial, (compression/tension). The rest of the force is seen in other directions that are perpendictular to the beam's axis, per my previous illustrations. Thus the force applied breaks down into components that are axial and perpendicular to the beam. Now if the beam itself is allowed to swivel (deflect) then the forces in the perpendicular direction cause motion in those directions and the beam swings. And no, no stress is induced into the beam in that direction until it's movement is hindered. However, if the beam is not allowed to deflect (like in a four-link suspension where the links cannot deflect side to side) then those component forces that are perpendicular to the beam's axis turn into bending loads. That's what I'm talking about here, not trying to twist the beam at the ends but rather pushing the beam sideways and not allowing it to swivel. That's the bending loading I'm talking about.

[ntsqd]

Hoo boy... Here we go with the engineers...

Hoo boy, Here we go with the Anti-Engineer... :D

It's "Damperening", dammit!

Seriously though, think about how the two sets of tabs are NOT directly inline with the force direction. That is the key to understanding why the link would bow in bending even though the ends are free to rotate about axis' parallel to the centerline of the bow's arc.

EDIT:Outcast, perhaps a Force Vector Diagram, only leave off the fancy math? Say a 3-4-5 triangle? Pythagoreas is at play here and he LIKES to multiply loads and just generally run amuk.

Further EDIT:Think it it this way, a 3-4-5 right triangle. The 4 is the direct loading, the 5 (hypotenuse) is the compressive loading. That leaves the 3. It turns into a moment b/c of it's direction and distance from either end.
Now consider that each end of the link is free to rotate, but the pair of ends limits that freedom. The only way for the link to rotate about the ends is for the link itself to bend and for the tabs to move closer together. Coincedentally the force direction is helping to move those tabs closer together.

[FABRICATOR]

The arrangement or movement of a beam is not relevant. If a simple beam is mounted between centered and freely swivalable ends, and does not contact anything between those ends, there are only two forces outside of buckling, that can act to bend it. One is friction of the swivel ends; the other has to do with the laws of inertia. Link components of a proper 4-link system do not experience high inertial loads.

Swivel rod end friction can, on rare occasion, be quite substantial and cause “unexplainable” part failures up to and including breaking a shock absorber shaft. However, even if you have a rod end that is substantially seizing, it will not bend an average tubular suspension link, but would cause failure at or next to the rod end.

"Swivel: a device joining two parts so that one or both can pivot freely." (even under load)

[Josh_K]

Hay man, I am not anti anything.

Some times thou a smart but otherwise average person that happens to have a good education and an engineering degree can tend to "think they know it all". In many ways I wish I had the education and training too. But instead I use some not to common "common since" to solve my engineering issues. Sure lots of times I go heavy to solve the issue but as Rod Hall once said, “I have never seen a truck built too strong broke on the side of the trail”.

And just so all of you know, one of my hero’s of the aviation world is Kelly Johnson, lead aerodynamic engineer for Lockheed thro the 40’s 50’s 60’s and in to the 70’s. What I think makes Kelly such a great engineer is that he would have Toni Laveer (Lockheed’s lead test pilot thou the 40’s, 50’s, 60’s. and civilian race pilot) take him up about once or twice a year and scare the hell out of him. He said it always kept him grounded on all the far out ideas that he wanted to do or try.

BTW, Kelly was the guy that designed the Electra, P38, U2, X15 and SR71 with out the use of a computer, just to name a few. But I am sure that he had the help of some other smart talented engineers too.

Josh

[matt_helton]

ok Josh, i just ordered that spell checker program for you. You should have it in 5-7 business days. :)

[ntsqd]

Hay man, I am not anti anything.

I WAS teasing. We've been at odds b4, but it's only b/c you're as stubborn as I am and won't concede that I'm right. :) LOL


"Swivel: a device joining two parts so that one or both can pivot freely." (even under load)

Because the swivels in this situation are mutually opposing and (in the above diagram due to outside parts) movement is confined to a singular direction (the Force direction), the "free pivot" no longer exists.

[Josh_K]

I know... I also know that I come off wrong at times

[matt_helton]

awww, im gettin all misty over here. :)

i love RDC!!!

[matt_helton]

jeez, im gettin all misty over here.

i love RDC!!!

[Kbach66]

And just so all of you know, one of my hero’s of the aviation world is Kelly Johnson, lead aerodynamic engineer for Lockheed thro the 40’s 50’s 60’s and in to the 70’s. Josh

Josh,
I'd have to agree with you on the Kelly Johnson being the man. I've got a Blackbird book that is signed by Kelly and the two authors. My dad worked at Lockheed and I'll never forget seeing the SR71 fly. I was also lucky enough to see it do it's final flyby at Burbank in the late 80's and it was an amazing site.

Alright....back to the bickering about forces, loads, bending blah blah blah.
Sorry to kick it off topic.

Oh....I'll put it back on topic....I'm an engineer :)

[FABRICATOR]

K. Johnson is my hero too. Skunk Works by Ben Rich is a must read!

T/S, you are right, the beam ends are mutually opposing…
But, where did the pivot function go?

[ntsqd]

They're still there, but they are locked out by the beam being attached at both ends and the constraint of allowable motion only in a single direction that is not down the link's axis. The geometry of the design forces a bend in the link even though the ends are free to pivot.
If the upper tabs are allowed horiz translation relative to the lower tabs, then the moment goes away and all that is left is the compressive loading of the link.

That Johnson and team did all of the 71's thermal growth calcs pre-computer is mind boggling. I once got a cool tour of a hangar that housed, among other muy interesting aircraft, the only twin stick 71 ever built. Even got some of it's fuel in my hair. Sitting next to it was a 'std' 71 that was fitted to test the Linear Rocket motor slated to power the shuttle's replacement.

[rokker]

...is the correct terminology to dampen or dampening??

Gosh I remember that one... LOL

[Josh_K]

My personal KJ favorit is the x15. Just think that this was flying out of our atmospher into space and returning in 1965. Guys like Scott Crossfield actually were awarded astronaut wings for the flights. I think the were over 265,000 ft. Today they ("The Man") will tell us that it was data colletion for the shuttel. But think about this.

In 1903 we had the first flight. 62 years later we have things that can fly into space and glide back home. Now its a full 40 years later and I am guessing that the Gov. has it figured out to the point that they have AC that do a missions simular to some thing out of Starwars. Fly into space (low otbit) manuver and shot down satalites or ICBM's???

I know, I am just dreaming. Purly speculation.

Josh

[Racer277]

I once got a cool tour of a hangar that housed, among other muy interesting aircraft, the only twin stick 71 ever built.
I thought there were two 71B's, and one 71C.
Didn't they all have two sticks?
I stood under one (for shade) on the flight line at Dryden while we watched a shuttle land...

[Stephen]

Is there a chance that our nye scholar has been working on applying ME101 so we can get back to the subject of forces on links without having to teach that you can't bend on a link with hiems on the ends?
I only mean this slightly sarcastically, you deserve a little leeway for trying to think about this but also some harassment for arguing about it too long without figuring it out.

As for the "put the links where you want" statement, you still have to have some idea what you're doing to the other parts. If your math indicates that a 1.5 x .120 tube will buckle, use a 1.75 x .120 tube. That's an easy problem to solve compared to messing with a roll center or squat problem since the latter problem usually involves moving mounting points.

One issue we haven't looked at here is weight. If you're mounting a coilover and bypass shock on the link arm, you can drop all that weight (plus the mounting structure) in the chassis by several inches by mounting the lower link arm under the rear axle rather than in line or above. I think it would be a factor worth considering.

[FABRICATOR]

..you deserve a little leeway for trying to think about this but also some harassment for arguing about it too long without figuring it out.

Everyone does have it figured out, they just didn't come to the same conclusion. Maybe we could have something more scientific, like a consensus.;)

You can see a real SR71 trainer (2 seater) up close right in the middle of Los Angeles at the Science Center. It is not black because it is outdoors and they don't want to paint it all the time. It's kind of a titanium color... quite impressive.

[ntsqd]

Perhaps bending is being confused with Buckling? The net result is the same no matter how you get there.

If there's one thing about Engineering that drives me crazy it's the stupid, non descriptive nomenclature. "Moment" intuitively makes zero sense to me. Call it a "torque" or a "leverage" or something that paints a damened picture so that I know what's going on.

Every 71 started out as a two seater, but the NASA guide told us that there was only one built with 2 control sticks. It's distinctive b/c the rear seat is higher than the front seat and has it's own forward facing glass. In all of the others there is an actual bulkhead btwn the two astronauts flying it. The rear seat may be able to fly by instruments, but can not see thru the forward facing glass. It was intended to be a trainer. I do not know if it ever got used that way.

[Racer277]

Every 71 started out as a two seater, but the NASA guide told us that there was only one built with 2 control sticks. It's distinctive b/c the rear seat is higher than the front seat and has it's own forward facing glass. In all of the others there is an actual bulkhead btwn the two astronauts flying it. The rear seat may be able to fly by instruments, but can not see thru the forward facing glass. It was intended to be a trainer. I do not know if it ever got used that way.

Ah, I see.
That's the one I stood under at Edwards. This was mid 90's, they told us that a husband and wife team flew it, can't remember why. It was definetly distinctive with the 2nd canopy.

Sorry for the thread jack, back to the axle housing-very interesting stuff.

[Josh_K]

Yes that is true a husband and wife did fly it. All the mission that they flew were for NASA thou. Some thing about sicance and a global warming.

At the time I was big into flying acro and the two pilots that flew it were big time and serious acro pilots too. They were trying to get on the US acro team. I forget there names, but I remember they had a super stinker Pitts that could fly out of the top of an acro box on the up line. At the time I had 180hp flat wing that wouldnt roll and pooped out after about 1200 vetical ft with about 200 mph of smash.

[Kritter]

Sub-atomic "string theory"

B.T.W. Mr. OUTCAST,
When talking about shocks, is the correct terminology to dampen or dampening??

Neither..it's damp and damping.

Not to Chuck or D8D but to the so called grads...

I dont have time to go thru these shenanigans but I want to know what "engineering school" teaches 4 link suspension? Thats something that would be learned at a tech school or some kind of specialized school for automotive. If they did teach 4 links it would be touched on...not in depth and if it was in depth it would be more of a mechanical linkage system used in machine design, not automotive. If your school did teach it I would like to see the syllabus.

and something connected at two points is a 2 force member meaning forces only act upon it thru a line between the two points...thats entry level statics class or the first part of a physics class. Dont give engineers a bad name by spouting off things you dont have a clue about and use your degree as a scape goat for ignorance.

Yes I am an M.E. grad. with honors.

[Chris_Wilson]

Exactly Kritter. Nuff said.

[Hollowpoint]

Everyone does have it figured out, they just didn't come to the same conclusion. Maybe we could have something more scientific, like a consensus.;)

THE most intelligent comment made in this thread by far, IMO.

You don't have to go through the shenanigans or whatever the F that is. But others may. You're welcome to leave the classroom when your curiosity/patience is satisfied. No one's going to miss ya. Some of us aren't ME majors.

[Outcast]

I'm well aware of the two-force, axial model, it makes things much easier to visualize. And yes, when you use that model, you can see that the reaction force in the link mount magnifies the axial load thus making the axial load greater than the load applied laterally. And yes, the greater that angle gets, the more the axial load is magnified, meaning the link is put under greater stress and thus put closer to the critical buckling load. However, I look at it from the same perspective that ntsqd does and see the bending moments. Call them internal, inertial, what have you, but they are also magnified by non-axial loading. Now you can say they are magnified because the axial load is magnified and such but that's really a chicken or egg discussion. It's magnified because of the compound loading, and I think that does answer the question that was asked, which was why do they bend so much especially in crashes? The compound loading, and the single point hits that are taken during crashes. Can that, at least, be the concensus?

There was no spouting off.. I only defended what I, and others were commenting about against someone calling it speculation and that was BEFORE the whole bending/axial arguement. I don't see the need for that comment...

My degree is from GMI, now called Kettering University. The class that "touched on" four-links was called Vehicle Design. I appologize as I no longer have the syllabus but I would think the title would be self explanatory.....

[Outcast]

Fine, Chuck. Links (not trailing arms with the coils mounted on them) don't bend they buckle. There, I concede your symantics, which is really all this argument was.

[ChuckH]

Fine, Chuck. Links (not trailing arms with the coils mounted on them) don't bend they buckle. There, I concede your symantics, which is really all this argument was.

We weren't talking about links with coils-shocks on them, of course they have a side load, we where taking about rod-tubes-links with two hiems on the ends.

the pic you posted showed the top links that where mounted in a V, you debated that it was the top links that had side loads because they where mounted in a V

The pic you posted

Quote of what you said ( that started this)
Well, 1) Since the upper links are usually converging, they are not loaded in simple compression along their axis. They are also loaded in bending


http://img14.imgspot.com/u/05/243/13/LinkLoad.jpg

[ntsqd]

Perhaps bending is being confused with Buckling? The net result is the same no matter how you get there.
The danged tube still bends under a compressive load. How do you KNOW it is due to buckling and not bending? The two pivots are constrained such that they can not move relative to each other, Except in the direction of the force vector by deflection of the tube. The true force vector is not coaxial with the tube centerline. That creates a lever length and combined with the non-coaxial force makes a bloody "moment", wtf that is.

Better yet, aside from enjoying a Euler experience, why do we care which it is? It's still bent.

[matt_helton]

im sooooo glad this thread is still going........:) good stuff guys.

[Outcast]

We weren't talking about links with coils-shocks on them, of course they have a side load, we where taking about rod-tubes-links with two hiems on the ends.

Yes, Chuck, I know that... I made the caveat about links with the springs/shocks mounted on them because if we are going to restrict each other to "proper" terms then those links don't apply to this discussion because they are not "two-force" members. Had I simply stated that links don't bend they buckle, then sure enough, someone would jump in an say well that's not totally true because links with coils, blah, blah, blah. I was only trying to avoid yet another holier than thou crusade in the pursuit of semantics...

You can calculate when a link or column is going to "buckle" but when it does, it sure looks like bending....

[ChuckH]

Yes, Chuck, I know that... I made the caveat about links with the springs/shocks mounted on them because if we are going to restrict each other to "proper" terms then those links don't apply to this discussion because they are not "two-force" members. Had I simply stated that links don't bend they buckle, then sure enough, someone would jump in an say well that's not totally true because links with coils, blah, blah, blah. I was only trying to avoid yet another holier than thou crusade in the pursuit of semantics...

You can calculate when a link or column is going to "buckle" but when it does, it sure looks like bending....

No you said there was a side load on the top links, thats what everyone said you where wrong about, you even drew a pic to prove your point ( There is no side load like your pic shows )

Your just trying to change the subject now

Quote of what you said ( that started this)
Well, 1) Since the upper links are usually converging, they are not loaded in simple compression along their axis. They are also loaded in bending

[ChuckH]

ChuckH, Sometimes your posts are inflammatory and unnecessary.

I'll admit that my posts on occasion are also inflammatory, but my goal is always better understanding, not name calling. Please consider deleting it and I'll delete this.

Ever hear of PMing someone !!!!!! OK now that you made me look like a dic by leaving yours up after i deleted mine ( people might think i said something worse than i really did )

This is what i said to outcast ( note i didn't call him ignorant like Kritter )

Bla Bla Bla, blather on all you want everyone knows your wrong, be a man and face the truth

[Outcast]

Your just trying to change the subject now


No, Chuck, that is still how I see it. You want to use the axial model, then use Euler's formula to calculate why/when the link bends, then call that buckling, fine. Like I said, I concede your semantics. But I still "see" it differently. Buckling looks and is the same as bending.... But, by all means, let's not call it that because someone has decried that axial members don't bend. What ever.

I was responding to your statement that claimed that I was somehow talking about both upper links and trailing links, which was not true. I simply explained why I made the links with coils qualification.

[ChuckH]

Ok, explain the side load in the pic you posted, on the tube-rod-link what ever you want to call it ( this should be good )

quit trying to change the subject to failure modes, note i haven't said anything about how it would collapse under a force behond the tubes failure point.

http://img14.imgspot.com/u/05/243/13/LinkLoad.jpg

[Josh_K]

I know I am at fault for this thread too but is this longest, stupidest and most points less thread that that has ever been in RDC Shop???

It has my vote.

BTW, guys like Chuck and I actually know what we are talking about form hands on experience. Not cyber space and theory in a classroom.

Josh

[matt_helton]

here, let me start the lockdown countdown.......10..9...8...

[partybarge_pilot]

7....6...5.... Burp, time to go do more research......

[Outcast]

Ok, explain the side load in the pic you posted, on the tube-rod-link what ever you want to call it ( this should be good )

I already did...
Thus the force applied breaks down into components that are axial and perpendicular to the beam. Now if the beam itself is allowed to swivel (deflect) then the forces in the perpendicular direction cause motion in those directions and the beam swings. And no, no stress is induced into the beam in that direction until it's movement is hindered. However, if the beam is not allowed to deflect (like in a four-link suspension where the links cannot deflect side to side) then those component forces that are perpendicular to the beam's axis turn into bending loads. That's what I'm talking about here, not trying to twist the beam at the ends but rather pushing the beam sideways and not allowing it to swivel. That's the bending loading I'm talking about.

[Josh_K]

4,...3,....2,....

[ACID_RAIN28]

1.......kaBBBBBBBBBBBBBBBBBBBBBBOOOOOOOOOOOOOOOOOM MMMMMMM!!

[matt_helton]

josh, we need to hang out and drink some beer.

[Josh_K]

I am working on the wife right now about doing a little late annual BBQ as we speak. Have faith, the wheels are spinning.

[ntsqd]

Anyone seen Fish's softball?

[Kbach66]

Anyone seen Fish's softball?


Damn you Thom, you beat me to it!!!

All I could think of about a page ago was "where's fish's baseball?"


mmmmmmm.......beer. Did you mention beer helton?

[matt_helton]

beer what?? lol

and yes, it was a "baseball" haha

[ntsqd]

Damn you Thom, you beat me to it!!!

All I could think of about a page ago was "where's fish's baseball?"


mmmmmmm.......beer. Did you mention beer helton?

Thot about typing "football" just to see who would remember.

Now I know the Secret Weapon against Helton. Just get on his race freq and say "BEER".......

LOL

[matt_helton]

mmmmmmmmmmmmmm beer...........:)

[J.JOHNSON]

Beer And Limp Bisquet Is All Matt

[J.JOHNSON]

Wasn't this thread about axle somethings or thingymajigs.

[matt_helton]

jeez Jake, at least you could spell it right..........its Limp Bizkit. HAHAA, i remember that time in glamis when you got all pissed at me. lol

[FABRICATOR]

Here's a picture of an unusual setup that includes the anti-sway bar. (sway-bar courtesy of photoshop :))

[matt_helton]

so adding all that extra unsprung weight isnt a big deal?

[Outcast]

so adding all that extra unsprung weight isnt a big deal?It depends on who you talk to. There's alot different views on that subject.

[matt_helton]

yeah, i know those rear ends are heavy as hell to start with then throw in the sway bar and links and its gotta weigh a boat load more......maybe its good for traction??

[Chris_Wilson]

Re unsprung weight, I think the most important aspect is the ratio of sprung to
unsprung weight, not so much what the absolute numbers are.

[ntsqd]

I think low unsprung can't help but be a good thing with regard to letting other parts live. It will reduce all of the loads placed on the linkage, springs, joints, and dampers. The dampers will be more fade resistant, the joints will have a greater strength margin, same for the linkage. It's a domino effect thru out the whole suspension system.

The problem is making those light parts live. How light is still strong enough? The ideal light weight race car falls apart at the finish line. I know danged few people who'd be willing to climb in such a car. Better to build it robust and know it will live and maybe even finish.

[matt_helton]

i think you meant to say "dampeners." hehe

[Josh_K]

I sware it was "DAMPENERINGGEERDINGGERS"

[toddz]

Here's a picture of an unusual setup that includes the anti-sway bar. (sway-bar courtesy of photoshop :))

Geisers' use that sway bar setup on all their trucks now.

Todd Z.

[FABRICATOR]

Keeping weight low does not have to mean making things weak. Except for Formula 1, any part for a racecar can be made lighter without necessarily loosing strength. This is done with better (dare I say it…) engineering, along with the usual increase in work and material costs. But overall component layout is at least as important as the parts themselves.

On anything faster than a farm tractor, adding unsprung weight does not help traction and should be minimized. More weight means slower response, less control, greater stress, and usually more sprung weight.

The sway bar here is certainly a compromise, but it very well may have been a practical choice in relation to the overall layout. Logic says it slows the car to some degree, but how much and how importantly is hard to tell.

[ntsqd]

i think you meant to say "dampeners." hehe

DOH!
Actually, it's "damperens", but still DOH!

I agree that removing weight doesn't necessarily weaken the part, but at a point pretty close to where most are now they'll need some semi sophisticated to outright sophisticated analysis done to do this w/o weaking the structure. That's not something everyone here can do, or even has the tools to do so with. So my comment was pointed more towards the amature fabricator (meaning not paid to do the work rather than poor work quality) than what any of the reputable shops can do. A certain amount of this can be done by the "Eyeballic Method" (tm), but there are near limits as to how far this can be taken unless the eyeballisizer has considerable experience in lightweight fabrications. That's not a catagory I class myself in.

[SANDlessNSeattle]

Ok if a bear is taking a crap in the woods......and is dumping "unsprung weight" are his or her knees bending or buckling from the stresses of the unsprung weight.....and furthermore when the crap hits the ground is it being dampend by this action or is it just having a dampeninng effect?????

[knucklemeat]

Ok if a bear is taking a crap in the woods......and is dumping "unsprung weight" are his or her knees bending or buckling from the stresses of the unsprung weight.....and furthermore when the crap hits the ground is it being dampend by this action or is it just having a dampeninng effect?????
and for the bonus question,is the bear uilizing squat or anti-squat?

[SANDlessNSeattle]

DAMNNIT I left that part out .......good point dos

[matt_helton]

just when i though this thread was done and couldnt produce anymore laughs.......:)

[down4glamis]

awesome thread, though there was alot of bickering involved. i know its old, but applies to my situation...

My upper link mounts(on the housing) are ripping off(cracking to say) and are cracked at the front, so the load is pushing the mounts back. I mounted my lower links at center line on the housing per recommendation from Nestor(from newline). he did a calculation of lower link mounts(on the frame) relative to the upper link mounts, relative to the shock placement. now I am curious if i had mounted my lower mounts(off the housing) lower than center line if it would be relieving the stress placed on the mounts? if i change them(I wont be) but if i lowered them, how would that affect anti-squat and any other variables. my distance between the upper bolt line and the lowers is 6". i was told that i need to have it less than that, or right at 6" no more, since i already mounted the lowers(on the frame). i am going to throw more plate at the mounts, and make sure they do not continue to crack, but this is just building it to last, not building it right. any advise?

second, my truck was built by Rick Holmes(Jesse Jones TT in Skunk works thread) and he utilizes the same sway bar setup off of the housing instead of having the torsion on the frame rails(on a truck w/ a frame still) and having the arms run to the housing and down. What is the advantage to that setup, and is the unsprung weight added and drawback?

I am by no means a engineer(21yrs old) but have learned alot through knowledge able people, and by asking good questions. i hope this will help me learn more about the geometry and loads that are applied on a 4link and other suspension components...

Sean Kepler
#!475

[Outcast]

Yes, if you were to lower those bottom link axle mounts below the center line it would reduce the stress on the upper mounts. However, as you suspect, it will effect other variables.

If you were to lower the axle mount of the lower link without changing the frame mount, you would most likely increase the anti-squat. You would also increase the amount of housing rotation throughout the suspension cycle and also slightly change the roll center height. You will also change the roll center axis and will most likely have a little more roll oversteer or less roll understeer depending on the geometry as a whole.

The 6" separation, is this at the frame or the axle? Allot of builders recommend around 10" of link separation at the axle.

As far as the swaybar mounting there are different views to that. The two most popular reasons swaybars end up where they do are packaging constraints and trying to achieve a particular roll rate in the bar itself.

[down4glamis]

the 6" bolt seperation is at the housing, and there is about the same distance where the mounts are on the frame. the upper link mounts are about 6" back, and about maybe 3-4" above the lower link mounts. the truck handles superb and has no squat or lift at all. the 6" diffrence is at ride ehight, it does change through out the suspension while it cycles. i am goin to throw more plate at the upper mounts, and basicly add a gusset from the top of the truss(along the back side) that will have a gusset against the back of the upper mounts. (gusset as a triange shaped plate butted against the back end of the upper link mounts, and laying on the truss. which should keep the links from pushing/cracking off the housing). thanks for your input...