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-   -   Front bumpers and AirBags (http://www.wranglerforum.com/f274/front-bumpers-and-airbags-120162.html)

Jeepin Dave 10-29-2011 03:38 PM

Front bumpers and AirBags
 
Some front bumpers advertise crush cans and work with AirBag.
Is this a serious factor?
What happens if one has a front bumper that does not have this?

ESP 10-29-2011 03:41 PM

what?

DrCloud 10-29-2011 04:00 PM

I'm interested in this question, too.

Clearly, for truly serious offroad wheeling, uncrushed cans would go by the wayside quickly. But there's value in keeping the vehicle street-legal and -safe as well. HPH

kbwwolf 10-29-2011 04:03 PM

Quote:

Originally Posted by Jeepin Dave (Post 1702780)
Some front bumpers advertise crush cans and work with AirBag.
Is this a serious factor?
What happens if one has a front bumper that does not have this?

Crush cans are for low-speed impacts. Some bumpers, such as the AEV premium bumper, include crush cans (or make a provision for the OEM version, I'm not sure which).

They will not affect the deployment of the Jeep's airbags.

MTH 10-29-2011 04:03 PM

It's nothing. There are crush cans in the stock bumper, but they are unrelated to airbag deployment. A change of bumper won't affect the airbag.

Jeepin Dave 10-29-2011 04:47 PM

AEV:
The Wrangler has been redesigned for 2007, and AEV is ready with the parts and knowledge to take your new 4 door, or 2 door Wrangler to the next level of performance and styling.
Not just a pretty face. Underlying the stylish stamped steel bumper face is all the experience and knowledge of years of hard off-road abuse. Not just setting the new benchmark, we may have just turned the traditional cut and weld bumper industry upside-down. Constructed of heavy gauge steel, with a separate winch mount tucked neatly between the frame rails, this bumper retains the factory airbag crush cans and offers protection and style like no other.


Also the Mopar Accessory Catalog makes a point that their bumper works with the AirBag system.

Seems to do something, but not sure what.

kbwwolf 10-29-2011 04:53 PM

I thought that too, initially.

Then I did some research.

They retain the crush cans. That's it. Airbag sensors are not on the front of your Jeep, otherwise the airbags would blow every time someone got into a fender bender.

DrCloud 10-29-2011 09:19 PM

Uh, well, as I understand it, the purpose of the crush cans on the OEM (and other) bumpers is to provide a buffer for low-speed front-end bumps so as to avoid air-bag deployment when it's not really needed. But on the OEM bumpers, they crush once and the the whole bumper needs replacing.

It would be quite nice if somebody offered a bumper with replaceable crush cans -- which are less costly to replace (of course) than airbags. Partly this is for the money; partly because no one really needs an air bag exploding in his/her face unnecessarily.

Is there such a thing? HPH

jkaufman_95 10-29-2011 09:26 PM

Quote:

Originally Posted by DrCloud
Uh, well, as I understand it, the purpose of the crush cans on the OEM (and other) bumpers is to provide a buffer for low-speed front-end bumps so as to avoid air-bag deployment when it's not really needed. But on the OEM bumpers, they crush once and the the whole bumper needs replacing.

It would be quite nice if somebody offered a bumper with replaceable crush cans -- which are less costly to replace (of course) than airbags. Partly this is for the money; partly because no one really needs an air bag exploding in his/her face unnecessarily.

Is there such a thing? HPH

An aftermarket bumper that isnt plastic will take a hell of a beating before it deploys the air bag

aelwero 10-29-2011 09:46 PM

Am I completely wrong in thinking that a JK measures changes in lateral G force in order to decide when to deploy air bags? I could swear I read that somewhere (I think it was in the users manual in fact). I've had my front bumper off three times now, and I assure you, there aren't any sensors in there... you have two crush cans to absorb impact, but even if you don't retain them, the entire front section of the frame is dimpled every few inches so in an impact, it is going to accordian itself backwards and will absorb a whole heckuva lot of force in the process...

If the airbag is activated by excess G force, as I think it does, then it won't matter what you have hanging off the front of the frame or how solid or forgiving it is...

jkaufman_95 10-29-2011 09:48 PM

Quote:

Originally Posted by aelwero
Am I completely wrong in thinking that a JK measures changes in lateral G force in order to decide when to deploy air bags? I could swear I read that somewhere (I think it was in the users manual in fact). I've had my front bumper off three times now, and I assure you, there aren't any sensors in there... you have two crush cans to absorb impact, but even if you don't retain them, the entire front section of the frame is dimpled every few inches so in an impact, it is going to accordian itself backwards and will absorb a whole heckuva lot of force in the process...

If the airbag is activated by excess G force, as I think it does, then it won't matter what you have hanging off the front of the frame or how solid or forgiving it is...

You are correct sir, that's also why your airbag doesn't deploy if you hit your bumper against something offroad not enough g's

KarlG 10-29-2011 09:53 PM

Lot's of misunderstanding here, in this thread. The purpose of the crush cans are to dissipate frontal impact energy and decrease an accelerometer reading from a decelerating impact to keep from triggering an airbag deployment below a moderate to severe frontal impact.

Frontal crush cans are designed and tested by an OEM bumper manufacturer with their airbag sensors to meet federal standards to prevent an airbag deployment from a frontal impact below a desired level.

Pretty much all aftermarket Jeep bumpers without crush cans don't meet any of those standards and are "off road use only".

AEV and ARB are the only bumpers that I am aware of that incorporate crush cans into their design. ARB has you reuse the crush cans from your stock bumper by cutting them out and AEV includes new crush cans.

Less impact energy in a frontal crash will deploy the airbags in a vehicle with a bumper without crush cans resulting in an airbag deployment. If the impact misses the crush cans, less energy (deceleration) will deploy the bags than if the impact deformed the cans and decreased the deceleration, even on a bumper with crush cans.

Lets throw some hypothetical numbers out. The OEM designs the system (with crush cans) to fire the bags with a frontal impact deceleration equivalent to a 14 MPH hit into a solid object. A 10 MPH hit through the crush cans, does not fire the bags. A 3 MPH hit doesn't fire the bags,

An aftermarket bumper without OEM cans gets a hit at 14 MPH-bags fire. A 10 MPH hit-bags fire (for example here). A 3 MPH hit doesn't fire.

Testing? I would bet most if not all aftermarket bumpers undergo no crash testing. The crush cans will also serve to dissipate some frontal collision impact energy from being transmitted to the frame that they mount to.

Since my jeep is a DD and see's more road use than trail use, I opted for a front bumper with crush cans.

Quote:

Originally Posted by DrCloud (Post 1703522)
Uh, well, as I understand it, the purpose of the crush cans on the OEM (and other) bumpers is to provide a buffer for low-speed front-end bumps so as to avoid air-bag deployment when it's not really needed. But on the OEM bumpers, they crush once and the the whole bumper needs replacing.

It would be quite nice if somebody offered a bumper with replaceable crush cans -- which are less costly to replace (of course) than airbags. Partly this is for the money; partly because no one really needs an air bag exploding in his/her face unnecessarily.

Is there such a thing? HPH

You got the crush can thing down, the AEV has welded cans and the ARB can could be replaced if you wanted to cut one out of another stock bumper and mount it theoretically, I guess. Most likely the bumper and mounting location would be deformed though.

jr1 10-29-2011 11:30 PM

From AEV forum ("AEV Dave"):

"The above is basically correct. In North America the JKs are set up with an airbag system that cannot by law deploy under 6mph for safety reasons when hit directly on the frame rail which would be the hardest jolt. The Crush Cans are designed to prevent that deployment. In a high speed collision the NAFTA JK airbags would work fine with a MILSPEC Bumper.

Export JKs and J8s use a totally different set of guidelines and airbag software and do not have crush cans.

dh"

American Expedition Vehicles - Product Forums - View Single Post - Question about MILSPEC Front Bumber w/out crush cans

El Gringo 10-30-2011 11:54 AM

also, the crush cans are small, and in front of the frame rails, roughly. So unless you hit the bumper directly on the can, they are useless. If you center up your vehicle and hit a tree right in the middle, it doesn't matter what bumper you have (with or without crush cans) the airbags will deploy or not deploy the exact same. The crush cans are a great concept, but only work if you hit them. Otherwise, they are useless and add weight (negligible, but they are pretty heavy).


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