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

[inVERt'D]

Front LCA Crossmember

Still more to do to the rear suspension, but I had to prioritize my argon and I really want to get rid of those Teraflex arms up front. On to the front 3-link.

I've already dropped some hints, but my 3-link is going to be a little different than your typical TJ's. I'd looked forward to following convention and doing things fairly simply. Just some typical LCA brackets on the frame rails. Some extra holes in the UCA brackets. The more I thought about it, though, the more I wanted to take the roll-oversteer out of the front suspension, and that meant moving the frame-side LCA mounts inboard. What I needed to do that was a front crossmember. With that big ol' 4500 under there, there's only one place to put a crossmember without it doubling as the transmission mount, and that's right in front of the transmission, and under the neck of the bellhousing. So the crossmember had to be bolt-in.

It's a tight affair, but there's room. Gonna have to re-route that exhaust, though. Wouldn't you know it, though, there's a dog-leg in the frame right where my bolt-in crossmember needed to go.


Well, I got to designing, and calculating and reckoning. Force will be coming from the front and from below. First thing I decided was that the bolts should go fore-to-aft (or aft-to-fore) so they wouldn't be in sheer. The crossmember would go in from the bottom. The bracketry would hold the crossmember in place securely front, back, and top. The basic crossmember would be a piece of 2”, .250” wall square tubing. Would have preferred completely fabricated out of 1/4” or better plate, but I didn't have what enough, let alone what I wanted, so I'd just have to reinforce the 2x2.

From there I played with a number of variations of design, both in my head and on the computer. Two bolts, three bolts, five bolts (adjustable height), different dimensions. Again, my entire design was built around the materials I had on-hand that I could spare for it. I also designed for the future when I may build a replacement crossmember or two.

Here are a couple of drawings of the bracketry that are pretty close to what I've made in steel.

First the the top view. This is pretty accurate, except that this shows the 2x2 crossmember with two 1/4” laminates for a total thickness at the brackets of 2-1/2” . If and when I make another crossmember entirely out of steel plate, I want it to be 3” thick front to back, so I modified the design for two additional 1/4” laminates to take up the space. None of my drawings reflect that, however.


Now the front view. The two main bolts are 5/8”. Lower bolts are (to the bottom of the frame) are 3/8”. Drawing is to scale. The location of the exhaust and the shape of the adjacent radius are subject to change.


By now some of you may be thinking “That's great for the exhaust, but what about the your ever-loving driveshaft?” To which I say, this is a redneck rig, it has no front driveshaft, silly! Just kidding. The driveshaft will be a two-piece affair. Here's a diagram. I paid a professional to do this.

[inVERt'D]

Holey cow tipping!

I understand holey cows tip a lot easier.

[6spdYJ]

Holey cow tipping!

[inVERt'D]

When people look under my Jeep they'll say "Holey, holey, holey!"

[aw12345]

Then you simply add more holey stuff till it all holy, maybe that will work

[inVERt'D]

You know guys, I've been thinking...

What if that holey 2x2 crossmember isn't strong enough?



















:cactus::cactus:

[inVERt'D]

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.

Looks good and strong, Art. I remember when you added those braces. Looks like those LCA brackets are taking a good beating. I'm glad to know that you're glad you're did it, because mine probably hang down just a bit more. I just couldn't get the numbers I wanted with them higher or I would have put them out of the way. Same with my front LCAs.

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

Delinquents! At least you're not trolling on the internet.

ARSS™.

Is that pronounced "arse"?

Why yes it is! Silent 'e,' in the best English tradition, of course. In fact, if I change my mind and decide to run with the ball, I'll call my company Adjustable Redneck Suspension Engineering. I'm just afraid people would pronounce it "ars้," and I would have to constantly inform them that it's not French.

[Materdaddy]

Adjustable Redneck Suspension System

ARSS™.

Is that pronounced "arse"?

[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

[6spdYJ]

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

[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.

[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.

[RAT]

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

[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.

[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.