It's An OCD Thing, You Wouldn't Understand

[inVERt'D]

are you planning on re-enforcing that lower control arm cross member? There is a tremendous amount of stress on those when climbing. That will snap. I found out the hard way.

i agree with chuck. There are way too many holes in the cross member.

i told him that about 5 pages ago when we started discussing swiss cheese

I agree with all of you guys, and thank you for your input. I had decided to brace up the crossmember even before I decided to drill holes in it. It doesn't have too many holes, it has just as many as I want it to have . Neither is this thing overly complicated. It's just complicated enough to provide the functionality I want. Does the design present some problems? Yes, but they are problems with solutions. (It's a problem with a solution is sort of a mantra for me ).

I think the need for reinforcement is sort of a no-brainer when you consider that without holes, the 2x2, .250" wall crossmember is of similar strength to the 2" .250" wall links. If I need my lower links to be that strong, and two of them are putting pressure on the side of the crossmember, then it probably isn't strong enough (tubing being a lot stronger in compression than bending). Messing with things like Triaged's 4-link calculator just reinforces this. The DOM links don't have an overwhelming factor of safety when you figure in enough Gs to account for things like bouncing, falling, jumping.

The link brackets themselves will also be braced. They stick out kinda far, and I see the potential for them to put torque on the crossmember. This aspect of the design is part of what postponed me actually going through with it. However, it's a problem with a solution. I alluded to this a few pages ago as well.

So there will be (Lord willing and the creek don't rise) plenty of bracing for the lower crossmember. It's just being put off until later. For one, I have several different schemes bouncing around in my head. The other thing is, I'm working with pretty limited resources in some ways, so I have to prioritize things more carefully. Not that the bracing isn't important, but doing the front 3-link is moreso. Making the Jeep safer for the highway is higher priority than wheeling. Not that wheeling isn't important...

[aw12345]

David that tube without the holes is not strong enough, giving it the Swiss cheese treatment didn't make it better, however since you got all these holes brackets bolted to it going forward at an angle and Swiss cheesed to the frame somewhere and bolting this crossmember to the skid will help. That crossmember sees a tremendous amount of force pushing towards the front of the Jeep as well as upwards

[6spdYJ]

If he uses it as a rear attachment for a 1/4" thick flat belly pan that has a piece of 1/4x2" angle to stiffen and locate against the cross member with 1/2"-20 button head cap screws all the way through, it will definitely not bend. It'll weigh more than the M4 Sherman and need a 5.7 hemi to move it, but it won't bend.

[aw12345]

If he uses it as a rear attachment for a 1/4" thick flat belly pan that has a piece of 1/4x2" angle to stiffen and locate against the cross member with 1/2"-20 button head cap screws all the way through, it will definitely not bend. It'll weigh more than the M4 Sherman and need a 5.7 hemi to move it, but it won't bend.

It will I tried the bolting to the skid thing, bolts worked loose every wheelin trip. It takes good bracing to keep it from bending and twisting

[RAT]

I'm not bashing anything here. You have skills man. But you are reinventing the wheel here.
Take the advice of them that trod before you. The Swiss make great cheese. Cross members not so much.
Ill go away now.

[inVERt'D]

1/4" thick and it snapped with no holes. [ATTACH=CONFIG]1245[/ATTACH]

Ouch! Must have been fun getting that home/ or to its trailer. Besides the the thing that we all agree on, which is that a crossmember that size and thickness needs bracing, I can see two things that contributed to its failure. First, the captures are almost at the middle of the crossmember, which puts a much higher bending force than if they were closer to the frame rails. Second, it broke adjacent to the the forward part of the capture bracket (which formed a stress riser, or focal point of stress). As an aside, I like your grease groove.

Thanks for sharing that. What were you doing when that failed? Did you post up your new crossmember in your build thread?

[inVERt'D]

David that tube without the holes is not strong enough, giving it the Swiss cheese treatment didn't make it better, however since you got all these holes brackets bolted to it going forward at an angle and Swiss cheesed to the frame somewhere and bolting this crossmember to the skid will help. That crossmember sees a tremendous amount of force pushing towards the front of the Jeep as well as upwards

In short, I agree. Never planned it otherwise. There are three things that are a for-sure deal with the bracing, and you just mentioned them. The first and most important are diagonal braces to the frame just aft of the trans crossmember brackets. The second will be tying it into the skidplate. You're right, holes are handy, and I may as well use them. The third for-sure thing is a brace between the UCA hinge boxes that will double as a mounting position for the adjustable capture braces. I still don't have the sheet/ plate metal I need for this.

There are a several other ideas I've tossed around. These would be done in addition to the things described above. One is to run bolt-in bracing between the rear crossmember and the front crossmember (you probably noticed it sitting on the floor in one of the more recent pics). The problem with this right now is that the transmission crossmember is in the way, and I don't want to tie into that, not in its current form. I would have to make another transmission crossmember, which I'd sorta figured I'd do sooner or later anyway. Another idea involves a second crossmember forward of the first one, but I don't want to try to explain that at the moment. It would need a good drawing to do it justice. Finally (I think), I've even considered going a little juggy and tying it into the roll cage.

If he uses it as a rear attachment for a 1/4" thick flat belly pan that has a piece of 1/4x2" angle to stiffen and locate against the cross member with 1/2"-20 button head cap screws all the way through, it will definitely not bend. It'll weigh more than the M4 Sherman and need a 5.7 hemi to move it, but it won't bend.

I do think that's a good idea, and as I stated above, I plan to do something along those lines, but also with the diagonal braces (or "kickers" as construction-oriented might call them).

It will I tried the bolting to the skid thing, bolts worked loose every wheelin trip. It takes good bracing to keep it from bending and twisting

That's interesting about the bolts working loose every trip.

I'm not bashing anything here. You have skills man. But you are reinventing the wheel here.
Take the advice of them that trod before you. The Swiss make great cheese. Cross members not so much.
Ill go away now.

I know you're not bashing, and I appreciate the critique and the compliment too. Thank you . Honestly, I expected some flack for this thing and not just because of the holes in the crossmember. I had sorta thought it better to wait until the rear suspension was "done" before I posted it up, and that was one of the reasons I had held back on it for so long. As far as reinventing the wheel, yeah in a way I am, and that's part of the reason I poke fun at it, and at myself, and for the name of the thread itself. My problem isn't under-thinking things, but if anything, the contrary. On the other hand, it's innovation with a purpose that's personal to me. I wouldn't have built this or recommended it to anyone else, and I never plan to make another like it. No need to go away, by the way.

When you all see how the front crossmember turns out, I think you'll see that I understand the need to reinforce a 2x2 crossmember.

[dirtman13]

Ouch! Must have been fun getting that home/ or to its trailer. Besides the the thing that we all agree on, which is that a crossmember that size and thickness needs bracing, I can see two things that contributed to its failure. First, the captures are almost at the middle of the crossmember, which puts a much higher bending force than if they were closer to the frame rails. Second, it broke adjacent to the the forward part of the capture bracket (which formed a stress riser, or focal point of stress). As an aside, I like your grease groove.

Thanks for sharing that. What were you doing when that failed? Did you post up your new crossmember in your build thread?

Thankfully I just happened to trailer the Jeep on that trip. It happened on Gatekeeper at Calico.

At that time I really didn't have the time to deal with it so I had Leadfoot Josh make me this.


This is no way that will happen again.



Not bashing you at all but why have all the holes for adjusting? If your already playing with the links calculator why not figure out what you need and make it permanent? I can see having the uppers adjustable up and down but don't quite get why you have to have the lowers adjustable side to side.

[inVERt'D]

Thankfully I just happened to trailer the Jeep on that trip. It happened on Gatekeeper at Calico.

At that time I really didn't have the time to deal with it so I had Leadfoot Josh make me this.
[IMAGE]

This is no way that will happen again.
[IMAGE]

Not bashing you at all but why have all the holes for adjusting? If your already playing with the links calculator why not figure out what you need and make it permanent? I can see having the uppers adjustable up and down but don't quite get why you have to have the lowers adjustable side to side.

Nice, I like that! I like fabricated plate crossmembers in general. I don't think that's likely to break.

I know you're not bashing, it's a very good question, really, although I think I answered it at the beginning of the 4-link stuff. Messing with the 4-link calcs and a bit of studying suspension theory is what convinced me to go through all the extra trouble to make the Adjustable Redneck Suspension System.

Cliff Notes Version:
1) Inboard/ outboard lower link position changes roll-steer geometry, which is important for handling and safety.
2) The calculator tells you what your roll-steer geometry is, not what it needs to be.
3) Roll-steer geometry isn't the only thing that influences actual roll-steer. Numerous other variables influence roll-steer.
4) Besides roll-steer, there are numerous other variables that determine how a vehicle handles and corners.
5) There isn't one answer to what actual roll-steer should be.
6) Calculator or no, probably 95% of the people building 4-links out there are either guessing where to place their links or copying someone else who guessed. The other 5% are tight-lipped.
7) It's called suspension theory for a reason: it is a very complex subject, and there is no perfect understanding of it. The experts argue even over basic things.
8) Given a choice, I'm not content to follow the people in number 6. I want to experiment and learn--that's what turns me on. I also want to be able to adjust and adapt my Jeep to different conditions. The crossmember setup is part of that.

The values the calculator produces are sort of meaningless by themselves. They're also not the whole story. I mean, sure I can understand what 2* roll understeer geometry means, but how do I know how it will make the vehicle perform versus 1* I want to know what those numbers mean in a real-world, visceral, seat of the pants, practical sort of way.

The Food For Thought Version
As far as the adjusting holes go, moving the lower link positions inboard and outboard changes the rear roll-steer geometry. Further inboard makes moves the geometry further towards roll-understeer. Further outboard moves the geometry further towards roll-oversteer. Roll-steer geometry is also changed by ride height. For instance, a bone stock Jeep TJ's roll steer geometry is a bit of understeer both front and rear. Lift that TJ 4 inches, and now it has roll oversteer geometry. Of course, the roll stiffness of a vehicle will influence how much the sprung mass (body, frame, driver, engine, trans, etc.) of the vehicle rolls and therefore how much roll-steer will come into play. Assuming we don't want a vehicle that over-steers, how much under-steer do we want?

Too much oversteer, and a car may want to go sideways in a corner, not good, especially in a Jeep. Too much understeer and a car will tend to push straight through turns--not good either.

Roll steer geometry isn't the only thing that influences roll steer. We still have to take into account the tires and road (or off-road) surface. A car isn't on rails. In turns at speed, tires slip sideways on the road surface. At speed, tire deformation and side-slip play a big part in a vehicle's trajectory through a corner. Less traction = more side slip. The slip angle is a measurement of the difference between the direction the tires are pointing and direction the vehicle is actually moving. Related to this are toe-in, Ackermann geometry, caster, camber (mostly irrelevant to Jeeps), front-rear balance, wheelbase and track width, and of course, the road surface and the tires themselves.

Not to be forgotten is the driver himself. What are his skills? Does he know how to handle oversteer? Most people are better and compensating for understeer than oversteer. I've had oversteer in my Jeep and learned to deal with it, but I'd rather have a bit of understeer, but not a lot.

So if you've read this far, you hopefully grasp a couple of things. First, the science is imperfect. Even expert suspension engineers need to test and revise their designs. It's probably safe to say that no non-engineer is smart enough or even lucky enough to design an optimal suspension geometry without a good bit of experimentation. I'm not a suspension engineer. Second, simply changing one of the variables mentioned above, whether it's something like the tires or ride-height, or simply the road surface or type of driving/ wheeling, adjusting the suspension geometry can help compensate.

[RAT]

Well you go have fun with all that. Me? I'm gonna go wheelin...

[inVERt'D]

Have fun wheeling! I can barely afford to weld pieces of scrap metal together, let alone wheel it outside the yard, so I'm having the sort of fun that I can afford.

[aw12345]

I went this route for bracing 3 years ago has been happy ever since. Only change I made after that was dropping the rear arms at the
crossmember about 1.5". Which made it climb and hook significantly better.

[6spdYJ]

All this talk about rolling steers. All I can think of is cow tipping

[RAT]

All this talk about rolling steers. All I can think of is cow tipping

Been there. Tried that. I have the scars to prove it

[Materdaddy]

Adjustable Redneck Suspension System

ARSS™.

Is that pronounced "arse"?