Crumple zones and BullBars

[Schludwiller]

Ok. This should get everyone fired up for Monday.

I submit the following picture from Australia.

Here is the submitters comment:
guys i am assuming that the ARB's you are talking about are the "Airbag Compatible versions?
over in the land rover world many folks that have the airbag compatible ARB bumpers complain that the crush cans allow the bumper to severly rotate and the wings of the arb bumper end up digging into the fender. it isn't from winching, generally it's from digging the front end into the dirt when you are past your approach angle


now ARB also makes a "non-airbag compatible" version without the crush cans. it is quite strong and wont rotate as long as you use all three bolts and upgrade to a bigger bolt size so that there is no slop for it to move. it is however not avalible for the new discovery 2 only the disco1.

some of the disco2 guys have welded the crush cans ridged so it is more like the "non-airbag" version.

have any of you heard of this problem with Xterra arb's? any comments?
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Ok, this enters into the realm of making judements about a picture and information provided from one person, but.....

Isn't this the argument that has been going on for 2 years now about how ARB (the USA Xterra bar) extends past the crumple zones of the frame and uses (3 bolts) to strengthen the bumper?

Wouldn't a bumper that attaches in front of the crumple zones be a weaker design?

So my take on it is this. The ARB bull bar that is currently shipped to the USA extends past the crumple zones and therefore is not subject to the terrible result pictured above. However there is another bumper currently being promoted for the Xterra that only uses two bolts in front of the crumple zone. Wouldn't the two bolt design suffer the same fate as the air-bag compliant ARB?

[Matt Peckham]

as stated in your quote, the "crush cans" are part of the airbag compatible bumper. and since NOBODY has experienced said problem in an Xterra yet, it's not a problem. When it becomes a problem, you can spread all the negative facts you want, until then, they are just theories.

Bored?

[ChuckH]

My thought is that if you're approaching something beyond your approach angle, you shouldn't be moving that fast. My other thought is that although I don't think those lower bolts do a lot, I do think they may help reduce rolling of the bumper like that. Quite frankly though, if you hit something that hard, the sides of your fenders are going to be the least of your worries. And finally, that's a Disco and we all know the Xterra is better built! Um, yeah, that's it!

[ned946]

Originally posted by Schludwiller

Wouldn't a bumper that attaches in front of the crumple zones be a weaker design?

Why wait till Monday?

It would be nice to know where the failure point was on that pic. If it was the ARB crumple zone, then, no I doubt the mount location wouldn't make a HUGE difference. The Xterra frame is heavy up at frame horn location and should support a 9.5K pull.

If it was at the disco frame point......well what can I say? Trade it in for a Xterra!

I think it has been well argued that the "crumple zone" on the Xterra was likely designed for 2 4000 lb vehicles (what is the X weight anyway?) that impact into eachother at 45 miles per hour can absorb some energy. I don't know the math, but I'm willing to bet that the math there shows forces far greater than 9.5K?!?!?

I'm just a little bummed about my ARB getting a little bent up from contact (specifically the "L" portion on the verticle of the ARB....it looks more like a "J" now).

[Schludwiller]

Originally posted by Matt Peckham
as stated in your quote, the "crush cans" are part of the airbag compatible bumper. and since NOBODY has experienced said problem in an Xterra yet, it's not a problem. When it becomes a problem, you can spread all the negative facts you want, until then, they are just theories.

Bored?

Nobody has experienced the problem because so far every Bull Bar put on an Xterra has bracing that reinforces the bumper beyond the crumple zone. If the picture is an example of what to expect, I wouldn't be in a big hurry to buy one of the "air-bag compatible" ARB's.

From the guys post it appears that ARB makes two designs. One that attaches the bumper in front of the crumple zone, and one that extends beyond and reinforces the crumple zones. We have the 3 bolt reinforcing design here in the US (Australia is passing new legislation about Bull-Bars maybe that's the influence). The 2-bolt GC ARB's that MAXC put on their trucks had reinforcing brackets created to extend past the crumple zones.

I'm not that concerned about front "offroad" impacts with dirt, trees, etc, because it has already been stated the frame is strong enough to support those tolerances. Two-bolt or 3-bolt.

My concern is with winching. In certain stuck situations there are a lot more forces being exerted on the bumper/frame than your normal offroad impact. While at Sand Lake, Mosi was pulling Chris from an uphill position. Chris was at a sideways angle and sunk deep in the sand. During that pull Mosi's ARB was being pulled towards the ground as the frame flexed.

How would the bumper behave in that situation with the 2-bolt design?

[VaderX]

This is just a shot in the dark but do you guys think that he meant a crumple zone built in to the design of the arb. So not the frame of the vehicle giving but the actual bumper giving. On either side of where the winch mounts there are two circular holes in the steel. Could this be where the bumper is crumpling.

If he is discussing an air bag compatible bumper with a non-compatible one it seems he is referring to the arb itself and not the frame.

[Schludwiller]

Originally posted by Matt Peckham
When it becomes a problem, you can spread all the negative facts you want, until then, they are just theories.

Matt, I'm bringing it up because it's a real-world example of an issue with crumple zones and bull-bars. It's a good example because it's the same company with the same bar except for the difference in how it mounts to the frame. One fails more often, the other is stronger. Like Ned I wish they had pictures of the failure point. I also wish it was an Xterra. But certain conclusions can be gained from it, and I was hoping for insight from others on the failure.

If you can manage it I would appreciate any "constructive" feedback you might have, but please keep the rehashed XOC rhetoric to yourself.

[Schludwiller]

Gotta wonder what these guys are hitting so hard.

[Schludwiller]

Original message accidentally deleted. Reply below is Matt Peckhams not my own. -Schlud

Their site keeps hanging but I was able to get some better info. (Wouldn't it have been easier to explain the Disco bumper system to me than just throw a flame Matt? I am interested in learning despite what you perceive as some sort of agenda.)

Sorry, I was aware that the ARB was a crunching bumper, as opposed to a regular bumper mounted in front of a crunching section of the frame.

I will find out what is best with the Calmini, and if it needs support, I will add it. I'm gonna beat the hell out of it, well, maybe not the hell, but the heck!

sorry if I sounded "that way", but you sorta sounded "that way" first. man are there some silly ass icons on this board....

[ChuckH]

You know, it's entirely possible that the Discos have a very different system for triggering the airbags. The Xterra relies on deceleration, so the bumper on the front would have little effect on them no matter how they are built. The only difference is that your rate of deceleration would probably be quicker, so the airbags may fire more easily, but I'm thinking it would be a negligible amount. Anyway, perhaps the Discos have triggers up in the front of the frame rails or somewhere nearby that are triggered by the actual impact? You know, those British always have to be different! That could explain why the bumpers are designed to deform like that.

The other idea, of course, is that the Disco frame rails do not have accordians at the front like on the Xterra. Instead, perhaps they are solid but then the bumper system has the folding mechanisms built in and that all attaches to the solid frame. The ARB then would jsut replace the crushable part that is part of the factory bumper.

Just a thought or two!

[Schludwiller]

Originally posted by ChuckH


The other idea, of course, is that the Disco frame rails do not have accordians at the front like on the Xterra. Instead, perhaps they are solid but then the bumper system has the folding mechanisms built in and that all attaches to the solid frame. The ARB then would jsut replace the crushable part that is part of the factory bumper.

Just a thought or two!

As far as I can tell your second guess is what they have. I found the replaceable crush cans listed as a "feature" on corporate sites while looking for info.

[ned946]

Originally posted by Schludwiller

Now we just have to wait for Ned to go hit something hard or winch his Calmini above his garage to tell if there is any difference between the 3-bolt and 2-bolt designs. (I think Steve wanted to do something like that didn't he?)

I thought you were anti-flame? Nice try Schludwiller. Why are you anti-Calmini? (Calmini uses 3 bolts per side)

Now, this is exactly how my bumper looks.....after the first (and only) winch pull......using ONLY a 8K winch. Those round holes ain't round no more. Again, we will see in time (after someone gets the Calmini and REALLY uses it).


And I'm not too concerned about that Nissan crumple zone....it took this "heavy hit" from a red light runner fairly well (if you consider a Prizm a heavy hit?!?!?)


Just to think about the forces involved placed on that crumple zone. The prizm pushed my Xterra about 45 degrees from the impact point. And those are 11.5 inch wide BFG's (plenty of road grip there). Yes the frame horns were bent, but the crumple zone was not affected. The bend was behind the crumple zone.

[Schludwiller]

Originally posted by ned946


I thought you were anti-flame? Nice try Schludwiller. Why are you anti-Calmini? (Calmini uses 3 bolts per side)

Groan. I wasn't flaming you. I just meant that we didn't have any owners with the Calmini yet, and it would be a while before enough people had put the bumper through it's paces through normal use to see how it responds. The lifting an Xterra above your garage was a joke. I just forgot my

FOR THE LAST TIME I AM NOT ANTI CALMINI. I just don't like the "you can't ask questions about their design or have an opinion" attitude. I gave you some lighthearted crap about your ARB statement (in another thread), but from your reply realised you pointed out a weak area in the bar that I have run into too. I haven't had the bolt problem you've shown here (and I've done some pretty intense winching with mine), but if I called you a liar and a spreader of "negative facts" what would be the benefit to the board?

Anyway enough about that. So the Calmini has 3 bolts now? Do they all mount in front of the crumple zone? Didn't the earlier design just mount to the two bolt zones in front of the crumple zone like the first half of the ARB?

Thanks for the info on the crumple zones from your wreck. Do you have any ideas why your frame bent behind them? How was that repaired, and are you concerned about winching now?

[ned946]

Photopoint nuked my pics of the Calmini. They use the two side nuts on the frame horn and one at the tip of the horn.

I don't know how the frame was corrected.....just bent back I assume???? And if they were just bent back, wouldn't that be yet another comment on the "crumple zone" strength???? My frame horns were nice and straight. To be honest, I'm not too concerned about winching now that I have reinforced the ARB....but I was before. My concern was further elongating the ARB mount holes.

I don't know why I've had problems with my ARB....maybe cuz it was one of the first and 4 wheel parts had to sorta do some experimental drilling (sorta butch) to find the frame nuts. I do know that my ARB holes are elongated......exactly as the pic above shows as well (and in my mind reconfirms my suspicions).

My bonehead simple thinking is that with thicker material, hole elongation wouldn't be such an issue (as it is in my mind) and the bumper could take more hits (as all off-road Xterras will do due to the approach angle) before failure. So, the only issue that remains unanswered is what kind of force is required to cause the crumple zone to fail (and I think its a lot more than any pull will ever produce)?

[Matt Peckham]

Their site keeps hanging but I was able to get some better info. (Wouldn't it have been easier to explain the Disco bumper system to me than just throw a flame Matt? I am interested in learning despite what you perceive as some sort of agenda.)

Sorry, I was aware that the ARB was a crunching bumper, as opposed to a regular bumper mounted in front of a crunching section of the frame.

I will find out what is best with the Calmini, and if it needs support, I will add it. I'm gonna beat the hell out of it, well, maybe not the hell, but the heck!

sorry if I sounded "that way", but you sorta sounded "that way" first. man are there some silly ass icons on this board....