We sleeve and gusset our axles, why not our cages? - JKowners.com : Jeep Wrangler JK Forum
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post #1 of 74 Old 03-13-2017, 04:56 AM Thread Starter
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We sleeve and gusset our axles, why not our cages?

Specifically I'm thinking of the a-b pillar spreader bar on a stock JK. It seems from pictures after rolls to be the weak point, even if you add an aftermarket cage, unless you replace it. But has anyone ever just tried to strengthen it via some sort of sleeve? Without going to the trouble of a full aftermarket or custom cage?
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post #2 of 74 Old 03-13-2017, 07:14 AM
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Originally Posted by chitown35 View Post
Specifically I'm thinking of the a-b pillar spreader bar on a stock JK. It seems from pictures after rolls to be the weak point, even if you add an aftermarket cage, unless you replace it. But has anyone ever just tried to strengthen it via some sort of sleeve? Without going to the trouble of a full aftermarket or custom cage?
You're more likely just going to weaken it. Also, it is going to change how the entire cage and vehicle absorb energy during an incident. In short, it is probably less safe than leaving as is. Synergy is really the least costly and good option out there. That said, I've seen pictures of JKs that rolled in a highway accident and the stock cage held. Where an aftermarket or custom cage can help is to limit the damage from a roll.


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post #3 of 74 Old 03-13-2017, 07:41 AM Thread Starter
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Also, it is going to change how the entire cage and vehicle absorb energy during an incident. In short, it is probably less safe than leaving as is.
That was actually one thought I had. Kinda makes the poison spyder kit (or anything) that replaces the whole bar with something stronger sound like not a great idea unless you're strictly off-road.
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post #4 of 74 Old 03-13-2017, 08:11 AM
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That was actually one thought I had. Kinda makes the poison spyder kit (or anything) that replaces the whole bar with something stronger sound like not a great idea unless you're strictly off-road.
Yes, there's little doubt (at least to most people) that the completely unmodified stock cage is as safe as you'll ever get on the highway. The amount of engineering effort and testing that has gone into the modern consumer vehicle roll cage design is spectacular.

About the worst you can do for highway use is a traditional 4x4 full-cage. It has no crumple points and transfers too much force to the occupants. In that case, you'd best hope you have a 5-point harness, helmet, and HANS device on (in which case, it might actually be safer than stock, but that's completely impractical to most people for street use)

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post #5 of 74 Old 03-13-2017, 10:10 AM
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Yes, there's little doubt (at least to most people) that the completely unmodified stock cage is as safe as you'll ever get on the highway. The amount of engineering effort and testing that has gone into the modern consumer vehicle roll cage design is spectacular.

About the worst you can do for highway use is a traditional 4x4 full-cage. It has no crumple points and transfers too much force to the occupants. In that case, you'd best hope you have a 5-point harness, helmet, and HANS device on (in which case, it might actually be safer than stock, but that's completely impractical to most people for street use)
I could be completely off base here but it is really hard for me to imagine the roll cage having crumple zones. The whole point of the cage is to protect the occupant. Crumple zones are found on the front and back (?) of your frame to absorb energy in an impact. Crumpling of the cage would expose the occupant to the environment which wouldnt be good.


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post #6 of 74 Old 03-13-2017, 11:17 AM
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So we are clear, the stock cage is shit on every level possible. You correctly identified that spreader bar and the b-pillar as being weak. If one was to peel back the cosmetic covers on the sport cage, as I have done, you would be truly appalled. Thin, small diameter, low-quality metal that is bolted together. Really sad.

The JK falls under the NHTSA Standards for convertible vehicles. And as such is exempt from higher rollover protection and crush standards that apply to even such wimpy ass vehicles as the Prius.

So, when you drive your JK, you are basically driving a convertible. Reassuring right?

As pointed out earlier, with roofs and pillars less deformation is better. More strength will definitely help. No cage in our JKU as of yet, but the Synergy version seems to be the most robust. You need to take apart a good chunk of the Jeep to do it. And your weld skills had better be on. But doing it right is never easy.

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post #7 of 74 Old 03-13-2017, 11:33 AM
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Crumple zones are on the front and back. The passenger compartment is designed to stay intact as much as possible.

Saying that stiffening the roll cage is bad goes against this philosophy.
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post #8 of 74 Old 03-13-2017, 11:49 AM
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Originally Posted by christensent View Post
Yes, there's little doubt (at least to most people) that the completely unmodified stock cage is as safe as you'll ever get on the highway. The amount of engineering effort and testing that has gone into the modern consumer vehicle roll cage design is spectacular.

About the worst you can do for highway use is a traditional 4x4 full-cage. It has no crumple points and transfers too much force to the occupants. In that case, you'd best hope you have a 5-point harness, helmet, and HANS device on (in which case, it might actually be safer than stock, but that's completely impractical to most people for street use)

The NHTSA does not do rollover testing. What they do is give vehicles a rollover rating. It's nothing more than a mathematical formula that uses the wheelbase, width and CG to determine the likelihood of a given vehicle to roll.

The IIHS does not do rollover testing either. They do a roof-strength test, where a metal plate is pushed against a car's roof to determine whether it would easily collapse in a rollover.

You have to keep in mind that it's nearly impossible to do consistent rollover testing. As soon as the vehicle starts to roll, it's on it's own and there's no rhyme or reason to the path it takes. Front and side impact test are the same every time, so you're getting quality data.

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post #9 of 74 Old 03-13-2017, 11:54 AM
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I was always under the impression that the crumple zones were more focused on front and rear impacts in relation to vehicles travel. A roll over test should demonstrate the cars' roof being able to absorb the impact and withstand crumpling, subsequently encroaching of the occupants "live-able" space. Most of the roll cage designs I have looked at do more for roll over impact to the top of the Jeep than it does for anything else. If you are looking more at an "Exo-Skeleton" style cage that wraps the entire vehicle and hardens the structure then yes, you would significantly effect the crash characteristics.

I think these are 2 very different discussions, because if you modify anything i.e. bumpers, sliders, bolt on body protection you've changed the way it takes a crash. If you do a quick Google search of Jeep crashes and you'll see there is a difference in both stock vs modified however, what it doesn't show is the transfer of the kinetic crash energy and how it's transferred to the occupants.

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post #10 of 74 Old 03-13-2017, 12:40 PM
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Disclaimer: I have a Rock Hard cage. That being said, the reason I installed the sport cage was because there were multiple Jeep highway accidents, that included some with fatalities, and some without. Every jeep that had a cage that was more than stock, the driver survived. The jeeps without additional safety measures, the driver did not fare so well. I intend on playing with my grandchildren. For that reason, I chose to install a sport cage.
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post #11 of 74 Old 03-13-2017, 12:44 PM
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Maybe it's not called a crumple zone but I'm pretty sure a stock vehicle cage is designed to significantly deform in a roll or collision. If it was perfectly rigid, you'd die in every collision or rollover at high speed due to the g-forces unless you're wearing full race safety equipment. At least that's what I've always heard.
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post #12 of 74 Old 03-13-2017, 01:20 PM
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Originally Posted by christensent View Post
Maybe it's not called a crumple zone but I'm pretty sure a stock vehicle cage is designed to significantly deform in a roll or collision. If it was perfectly rigid, you'd die in every collision or rollover at high speed due to the g-forces unless you're wearing full race safety equipment. At least that's what I've always heard.
Look at pics of high speed roll overs of JKs; if you roll it at high speed, you're at luck's mercy that the roof impacts in the right place. That give is there because it's likely the minimal protection standard Chrysler had to meet.







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post #13 of 74 Old 03-13-2017, 01:36 PM
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Maybe it's not called a crumple zone but I'm pretty sure a stock vehicle cage is designed to significantly deform in a roll or collision. If it was perfectly rigid, you'd die in every collision or rollover at high speed due to the g-forces unless you're wearing full race safety equipment. At least that's what I've always heard.
I honestly think if you leave the front of the vehicle alone your not going to affect the "crumple zones" that are designed into the body and frame of the jeep. The forward crumple zone on a Jeep starts just forward of the A pillar and goes to the front wheel well. There is also specific holes in the frame for it to help with this. Maybe I'm way off but I don't see how a roll cage will change any of it unless it specifically bolts to the frame. I've seen more stories of people rolling over on the freeway and saying they faired better by having a roll cage than not having one. At the end of the day there are only 2 types of wrecks, ones you survive and ones you don't. I'm in the process of beefing mine up just for fact that the 2dr cage in the back is a joke.

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post #14 of 74 Old 03-13-2017, 02:00 PM
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Originally Posted by christensent View Post
Maybe it's not called a crumple zone but I'm pretty sure a stock vehicle cage is designed to significantly deform in a roll or collision. If it was perfectly rigid, you'd die in every collision or rollover at high speed due to the g-forces unless you're wearing full race safety equipment. At least that's what I've always heard.
You want the cage to retain it's shape around the occupants at all times. Basically keeping them in a bubble of safety. The entire vehicle around the cage can deform to absorb energy. That's where crumple zones come in to play. Once a cage begins to deform, it stops being a safety device and can, in the worst case, become dangerous.

Now here's the catch, and you've kind of touched on it already. A rollcage by itself can be very dangerous. It's the main reason drivers wear helmets in racecars. Installing "quality" closed cell rollcage padding anywhere any part of your body may come into contact with the cage will drastically reduce the chances of injury. Sad part is that you very rarely see padding used in a Jeep cage. That's just not smart.

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post #15 of 74 Old 03-13-2017, 04:05 PM
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I am waiting on my full synergy cage as we speak. I find it pretty funny or perhaps scary someone would believe you are safer with the factory roll bar than a full cage. But then people voted for Hillary also so there is that.
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post #16 of 74 Old 03-13-2017, 07:08 PM
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So Rock Hard's marketing is absolute 100% BS? Not saying it's impossible, but they're a somewhat reputable company...


"Why not replace the entire vehicle cage?

The answer is simple: crumple zones. The section of OEM cage that runs along the top of your doors from front to back has factory designed and DOT approved crumple zones that are designed to absorb impact during a roll over or collision. Without theses absorption sections your cage would "sheer" and not provide any protection. If we were to replace those with solid steel tubes, removing any absorption during roll over, your safety would be compromised. By retaining those crumple zones we can maximize their attributes and provide a more secure and safe system."

https://www.rockhard4x4.com/product_p/rh-1030-1l.htm
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post #17 of 74 Old 03-13-2017, 07:53 PM
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So Rock Hard's marketing is absolute 100% BS? Not saying it's impossible, but they're a somewhat reputable company...


"Why not replace the entire vehicle cage?

The answer is simple: crumple zones. The section of OEM cage that runs along the top of your doors from front to back has factory designed and DOT approved crumple zones that are designed to absorb impact during a roll over or collision. Without theses absorption sections your cage would "sheer" and not provide any protection. If we were to replace those with solid steel tubes, removing any absorption during roll over, your safety would be compromised. By retaining those crumple zones we can maximize their attributes and provide a more secure and safe system."

https://www.rockhard4x4.com/product_p/rh-1030-1l.htm
To answer your question. Yes, 100% absolute bullshit. It's just marketing crap. Their explanation doesn't even make sense. There is no such thing as a crumple zone in a cage. It doesn't have to make sense though, because they know 90% of their customers don't have a clue.

Look at the pics terrahawk posted and imagine what they would look like if the Jeeps simply had a B pillar "X" installed.

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post #18 of 74 Old 03-13-2017, 08:57 PM
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If one was to peel back the cosmetic covers on the sport cage, as I have done, you would be truly appalled. Thin, small diameter, low-quality metal that is bolted together. Really sad.
Actually, the tubing on the factory cage, at least on the door headers, is the same diameter and wall thickness as the Poison Spyder trail cage -- 1-3/4"x 0.120" wall, and it appears to be DOM. And most of the aftermarket solutions bolt together as well. Bolts are not inherently weak. Your whole JK is, for the most part, just "bolted together."

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So Rock Hard's marketing is absolute 100% BS?
I'm not calling BS on RockHard, but I'd sure like to see their source information for that claim.

Those pictures Terrahawk posted speak volumes. The main benefit to an add-in cage IMO is in the A-pillar hoop, however that's accomplished. In every one of those pictures, to one degree or another, the windshield frame collapsed in on the occupants. Forget the B-pillar, that A-pillar is like tinfoil. They're actually using the windshield frame as a stressed member of the occupant pod, but it's far from up to that task (as those pictures show). By adding in an A-pillar hoop, the buffer zone around the front seat occupants increases dramatically. That's why I have one.

I also find it really hard to understand why the current design of the OEM cage uses bent tubes in the rear sections without any supporting diagonal bracing. That's really a no-brainer, and standard practice for virtually any mechanical structure. Diagonal bracing adds strength. And in cage design, every bend and every joint needs a brace. Poison Spyder's add-in C-pillar (for the Unlimited) addresses that design flaw, is a fairly easy thing to install, and IMO is well worth the effort.

I think another point that should be raised in this discussion is the intended design purpose of the add-in cages. I think you'll be hard pressed to find any of them claiming to give any significant high speed protection. That's not their purpose. That's why most of them are marketed by some name like "trail cage" or similar. They're designed for LOW speed rollovers, and for that purpose they do a great job. No, they're not going to give you the protection of a full tube chassis, but they will almost certainly keep a bad day from becoming a tragedy in many trail rollover scenarios.

And about the "convertible" thing . . . really? Is there really anyone that didn't already know their Jeep is a convertible? That's kind of the nature of the removable top -- it's CONVERT-able. It used to be that a top was an option on a Jeep. Any top. As in, the base price did not include a top! And for a lot of those years, it also didn't include any rollover protection whatsoever. So it's actually kind of funny that we're sitting around nitpicking the strength of the B-pillar hoop of the OEM rollover protection system.

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post #19 of 74 Old 03-13-2017, 08:59 PM
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Interesting info from rock hard.

Makes me sad that they would say all that bullshit. Rock hard is a solid company that makes top quality gear.

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post #20 of 74 Old 03-13-2017, 09:05 PM Thread Starter
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Interesting info from rock hard.

Makes me sad that they would say all that bullshit. Rock hard is a solid company that makes top quality gear.
That also doesn't want to tell you what tube material they're using (and it's not DOM).

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post #21 of 74 Old 03-13-2017, 09:43 PM
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That also doesn't want to tell you what tube material they're using (and it's not DOM).
Ouch! Just bad.

Well I still like my RockHard skids...

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post #22 of 74 Old 03-13-2017, 11:49 PM
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Rock Hard links to Waya. They can fuck right off.
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post #23 of 74 Old 03-14-2017, 10:12 AM
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I feel honored that we have so many structural design engineers from Jeep weighing in on this very topic.

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post #24 of 74 Old 03-14-2017, 10:28 AM
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I feel honored that we have so many structural design engineers from Jeep weighing in on this very topic.

Lol


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post #25 of 74 Old 03-14-2017, 10:34 AM
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I feel honored that we have so many structural design engineers from Jeep weighing in on this very topic.
One of the other forums used to have a Jeep engineer access evening once a month. It was a question and answer session for a few hours.

I wish Jeep would still allow that.

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