Let's Argue About Roll Cages

mobil1syn said:
having spent a lot of time prepping a igor designed car that i had to pull the shocks to a steering pump out, i am suspect as hell with his designs being serviceable.
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You should have worked on the hedgehog, after that everything is easy. If that thing had any driveline problems during the race, it was done, on the trailer it went.

Or any Newhan pre-runner. It took a solid 6 hours to remove the headers on the white one that did the canal jump.
 
Bends: support it with a tube and it's fiiiiiiiiiiiiiiiiiiiiine. Given unknown variables with HAZ, sharp points concentrating stress, and the fact that you end up with a bunch of butt-welds on outside corners, I think a bent tube with a supporting bar is stronger. Especially from a Sanctioning Body's perspective where they can't control who made the damned thing. :flipoff2:

NFW I'm plugging this into any sort of a calculator to back it up with maths, just my noodle's first blush analysis. :flipoff2:
 
JR4X said:
I’ve made some colossal serviceability mistakes on builds, because of that I watch who builds stuff with working on them in mind. At Reno finals one time my brother and I R&R’d a TH400 in a Tribe car in under an hour, a car we had never touched previously. The Penhall car right next to it was getting a trans too and they missed qualifying because it took like 6 hours for all hands on deck to R&R it. Joe Thompsons UFO’s are also extremely well built and easy to work on in a hurry.
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One of the biggest reasons I wanted to build my own buggy from scratch. I found out the day before the first run that I had the wrong torque converter. I had the trans on the floor in under 20 minutes from fully assembled. Nothing worse than a rig that is poorly engineered for maintenance.
 
HYDRODYNAMIC said:
The introduction of the tube bender has set back cage design about 40 years. It weakens the structural integrity of tube. It doesn’t allow for proper node placement. It has become such a predominant tool in fab that people have been close minded to all the other methods of fabrication with tube.
There is a time and place for a bend or a slight bend more like a roll bend. Aerodynamics, arched bridges, arched semi trailer, cattle gates, fluid lines, and economics are proof that there is a time and place for a bend.
I personally gave an Irate salute :flipoff2:to the tube bender sitting on the floor when setting out on a no bend chassis.
The best thing that could have happened to the tube bender was the introduction of the tube laser. The ease of miter joints has slowly killed off the over application of bends.
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Every rock bouncer with 2000 lbs of tube is crying inside. :lmao:
 
Winchested said:
Every rock bouncer with 2000 lbs of tube is crying inside. :lmao:
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IDK dude...

There is a rock bouncer in my shop right now, made exclusively of .188 and .250 (or bigger) with brackets made out of 1/4 and 3/8 everywhere.
It's 8 years old, has been beat down plenty and is still straight as an arrow. Something to be said about overkill.

And yes, it weighs 5700lbs, but there are plenty of heavier JKUs driving around with a 3.8 and it doesn't phase anyone.

Also yes, it has a giant big block and it ****s on your crawl ratio :flipoff2::usa:
 
Bebop said:
IDK dude...

There is a rock bouncer in my shop right now, made exclusively of .188 and .250 (or bigger) with brackets made out of 1/4 and 3/8 everywhere.
It's 8 years old, has been beat down plenty and is still straight as an arrow. Something to be said about overkill.

And yes, it weighs 5700lbs, but there are plenty of heavier JKUs driving around with a 3.8 and it doesn't phase anyone.

Also yes, it has a giant big block and it ****s on your crawl ratio :flipoff2::usa:
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But is it competitive?

Just curious I don't know **** other than I like watching them destroy their **** on vids!
 
HYDRODYNAMIC said:
Even with bends that buggy wouldn’t look cool. Cool was thrown out the window along with the bender. Now if I cut the the roof line down about a foot and take out the rear seat, people might take it serious.
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(honest no prick questions)
Any math/FEA to back up the no bends method is stronger than the bend?

IMO the double A like in the Triton and Bomber posted above doesn't seem to be more less superior than the mitered solution.
I get the nodes are more focused on the cut/weld cage but is that really a factor when colliding with dirt at race speed?
Hitting a rock/plane would be different and could have negative effects considering force vectors but with proper connections I don't see there enough separation to matter.
 
Bebop said:
Why do we care ?
We're talking about roll cages strength and design.
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If all one is worried about is wether it will save your life in a crash, sure no one cares. I bet a Tim Cameron chassis weighs 1000 ish pounds less than say Plowboy. When the game is fighting gravity AND saving your life AND competing against the clock. Then I care a lot.

That’s why I like Bombers and JHF cars. You get to lose weight while still maintaining a safe space to survive a crash in. Just my personal preference anyway.
 
JR4X said:
If all one is worried about is wether it will save your life in a crash, sure no one cares. I bet a Tim Cameron chassis weighs 1000 ish pounds less than say Plowboy. When the game is fighting gravity AND saving your life AND competing against the clock. Then I care a lot.

That’s why I like Bombers and JHF cars. You get to lose weight while still maintaining a safe space to survive a crash in. Just my personal preference anyway.
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I agree.
But not all rock bouncers compete.

Some are just for hardcore trail riding fun.

And the Bombers and JHF chassies are well known for cracking at weld joints and needed regular check/maintenance/tube replacement. Being lightweight comes at a price. Even if it's not safety.
 
Bebop said:
I agree.
But not all rock bouncers compete.

Some are just for hardcore trail riding fun.

And the Bombers and JHF chassies are well known for cracking at weld joints and needed regular check/maintenance/tube replacement. Being lightweight comes at a price. Even if it's not safety.
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To be fair though....the way many of those chassis get pushed, something's got to give eventually anyway.

But I totally agree....comp is very different from trail riding and overkilling the parts on a trail rig means it will struggle more on some obstacles due to the extra weight but will likely hold up longer over time. Everything's a trade off and if you don't have deep pockets to constantly be rebuilding or chasing the latest trend, building something hella stout that lasts makes sense even if it does show its age after a decade.
 
Sean said:
To be fair though....the way many of those chassis get pushed, something's got to give eventually anyway.

But I totally agree....comp is very different from trail riding and overkilling the parts on a trail rig means it will struggle more on some obstacles due to the extra weight but will likely hold up longer over time. Everything's a trade off and if you don't have deep pockets to constantly be rebuilding or chasing the latest trend, building something hella stout that lasts makes sense even if it does show its age after a decade.
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Age exposes things you'd never consider as well. On my desert buggy I had a pair of tubes that completed a perfect triangle crack about a third of the way from the node (one towards the top, the other towards the bottom). I chalked it up to some sort of material issue, cut them out and replaced. Following season, they cracked again. Nothing from the eyeballoscope said these tubes should crack, as they were part of the roll structure and I wasn't crashing constantly, and why not right next to the node? Cut/replaced again with thicker wall tube since something was obviously up.

Couple of trips later, I was diagnosing an engine issue and just happened to be leaning on this tube while revving the engine. Holy ****, I was practically tased from the tube vibrating like a **********er (as in: 1" of deflection mid-span). Apparently the length of the tube just happened to match secondary vibrations from the solid-mounted 4-banger at 3-4,000rpm and caused some sort of natural frequency issue. Added a node mid-span and all vibration went away, no more cracking after 4 years of heavy use. Still crazy to see a piece of steel flap around like a guitar string.

Point being: there's a lot of things to consider in a chassis. Cracks don't mean weak, just means it's being used and something you didn't consider ****ed it. :flipoff2:
 
Sean said:
To be fair
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CarterKraft said:
(honest no prick questions)
Any math/FEA to back up the no bends method is stronger than the bend?

IMO the double A like in the Triton and Bomber posted above doesn't seem to be more less superior than the mitered solution.
I get the nodes are more focused on the cut/weld cage but is that really a factor when colliding with dirt at race speed?
Hitting a rock/plane would be different and could have negative effects considering force vectors but with proper connections I don't see there enough separation to matter.
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No science here just feelings and opinions which have no value but are good to argue with. Facts are too easy to cherry pick. Data can be driven by the experiment parameters.
You can’t easily put a splice plate in the middle of a bend to protect the already deformed tube from flattening out more. You can put a splice plate in a mitered node and transfer a point load on the edge of the splice and down into the tube below.
Rooflines matter. If you bend then the roof should cover the bend to protect it from denting. If you miter then the roof can end at the miter where the down tube immediately changes angle. So the impact is at an angle rather than directly on the top of the tube.
 
CarterKraft said:
(honest no prick questions)
Any math/FEA to back up the no bends method is stronger than the bend?

IMO the double A like in the Triton and Bomber posted above doesn't seem to be more less superior than the mitered solution.
I get the nodes are more focused on the cut/weld cage but is that really a factor when colliding with dirt at race speed?
Hitting a rock/plane would be different and could have negative effects considering force vectors but with proper connections I don't see there enough separation to matter.
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Any kind of bend in a tube will lower the buckling load of a tube in compresion and reduce its stiffness in tension versus a straight tube of the same span. Now, whether the buckling load is relevant depends on the length of the tube and whether the crushing load is higher than the buckling load. A supported node at a bend with a reasonably tight radius is likely negligibly weaker than the same node made with straight tubing, but the straight tube node will be stronger and stiffer to some degree assuming that the HAZ has not weakened the tube more than the bend would have.

I think really the take away here is that any bend in a tube should be at a supported node. Having an unsupported bend in the middle of a span is terible for strength and stiffness. Think of every bend and node as a spherical joint. Will the chassis still be structurally sound? If not, it needs more triangulation! :flipoff2:
 
'84 Bronco II said:
Any kind of bend in a tube will lower the buckling load of a tube in compresion and reduce its stiffness in tension versus a straight tube of the same span. Now, whether the buckling load is relevant depends on the length of the tube and whether the crushing load is higher than the buckling load. A supported node at a bend with a reasonably tight radius is likely negligibly weaker than the same node made with straight tubing, but the straight tube node will be stronger and stiffer to some degree assuming that the HAZ has not weakened the tube more than the bend would have.

I think really the take away here is that any bend in a tube should be at a supported node. Having an unsupported bend in the middle of a span is terible for strength and stiffness. Think of every bend and node as a spherical joint. Will the chassis still be structurally sound? If not, it needs more triangulation! :flipoff2:
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Perfect world, yes. I wonder about the combined HAZ and stress riser from the butt-weld in the "straight tubing bend" though.

Agree on your last paragraph: any bend, whether using a bender or not, is introducing ****tiness to your design. Support it accordingly!

HYDRODYNAMIC said:
No science here just feelings and opinions which have no value but are good to argue with. Facts are too easy to cherry pick. Data can be driven by the experiment parameters.
You can’t easily put a splice plate in the middle of a bend to protect the already deformed tube from flattening out more. You can put a splice plate in a mitered node and transfer a point load on the edge of the splice and down into the tube below.
Rooflines matter. If you bend then the roof should cover the bend to protect it from denting. If you miter then the roof can end at the miter where the down tube immediately changes angle. So the impact is at an angle rather than directly on the top of the tube.
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Are we talking about this from a chassis reusability standpoint, or general safety? Yeah, the tube might collapse more on an impact, but I don't think it'll smash flat like a pancake and cause unwanted mayhem as a result. As long as there's a node at the bend, shouldn't collapse much. Look at the A-pillar on a roll cage: there's an upper windshield bar, and hopefully a bar under the tube, and even possibly some gussets. How far can that tube collapse before it tries to shear the connected tubes?

I agree that the cut/weld bend would be stronger in an impact... Assuming you went out and crashed it right away. I'm curious on how it will take to years of vibration and abuse however. It's been decades since Statics for me, so no clue which one would handle the rigors of chassis duty better. To me, there's a reason you always fishplate any butt-joint on a frame, and a good rollcage on anything somewhat racy will be part of the chassis.
 
Bringing this up...

Starting to draw out my design for the CJ build. It's a 3 seater (centered rear seat) so back seat access is semi-important. The diagonals coming down from the B pillar go through the fender tops and to the frame.
cage4.png
cage3.png
cage2.png
cage1.png


This is what I've come up with so far. Advice, suggestions, location of the nearest busload of nuns?
 
RSWORDS said:
Bringing this up...

Starting to draw out my design for the CJ build. It's a 3 seater (centered rear seat) so back seat access is semi-important. The diagonals coming down from the B pillar go through the fender tops and to the frame.
cage4.png
cage3.png
cage2.png
cage1.png


This is what I've come up with so far. Advice, suggestions, location of the nearest busload of nuns?
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Is the double V in the B hoop going to shock mounts?
 
RSWORDS said:
This will be the underside

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Those verticals kinda defeat the purpose of the diagonals. You would be better of with an A hitting the B pillars at the door bar. Then a single bar from the shock mount to the B pillar corner. Get the side to side strength back with diagonals from the B pillar at the door bar down to the floor bar the seats are mounted off of making a diamond.
 
RSWORDS said:
This is what I've come up with so far. Advice, suggestions, location of the nearest busload of nuns?
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The c roof/downbar/pillar structure bugs me. I want the downbar to either hit at top of the b hoop or at the bend at the back of the c at the roof, and you have it between. I really don't like that the c surround has what appears to be an unsupported miter/bend just kind of diving-boarded out there roughly next to your backseater's head, and really want to land the downbar there even though on the b pillar would probably be structurally better. On my own, I'd probably do both: land full diameter tube on the bend, and a size-smaller straight diagonal from the bottom of the c to the top of the b on the side.

I'm also confused, as you have some bends and some miter joints depicted, but I'm seeing miters a couple places that I'd expect to be bends and vise-versa. Is the bend/miter thing as intended or is it more of "didn't get to that detail level yet"?
 
ScottRS said:
The c roof/downbar/pillar structure bugs me. I want the downbar to either hit at top of the b hoop or at the bend at the back of the c at the roof, and you have it between. I really don't like that the c surround has what appears to be an unsupported miter/bend just kind of diving-boarded out there roughly next to your backseater's head, and really want to land the downbar there even though on the b pillar would probably be structurally better. On my own, I'd probably do both: land full diameter tube on the bend, and a size-smaller straight diagonal from the bottom of the c to the top of the b on the side.

I'm also confused, as you have some bends and some miter joints depicted, but I'm seeing miters a couple places that I'd expect to be bends and vise-versa. Is the bend/miter thing as intended or is it more of "didn't get to that detail level yet"?
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Yeah this is a general shooting for about this kind of design.....
 
The v things in your b hoop are basically your only lateral triangulation, are big enough to impede/prevent backseater in/out through there, and are dropping onto (if I understand correctly) a plate atop a foot tall column to the frame? I don't like that combo. I'd like it more if you split the v and run the inboard leg of the v to the frame at the bottom of the column underside tube that you've shown, or to a vertical plate at the bottom of your column tubes. You can drop the outboard leg on the plate you have if you want.

Have you measured for width and length yet? I see you have it drawn as square with the windowsill and the roof being the same width; mine is narrower at the roof, and is still too big to fit under a soft top. If you want to clear a soft top, you'll likely need to be smaller yet and I suspect narrower at the roof than the windowsill, but may also depend on doors (soft/hard/none/skin/??).
 
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