I'm not completely understanding the issue here.

So if the OEM bumper is designed to crumple, this helps reduce the rate of deceleration. If you have a Rock Lizard or Sundance Customs or any other aftermarket bumper (except ARB), the giant piece of steel you have on the front will not absorb impact as well as the stock crumple zones. This should make the bumper more sensitive to the impact of a head-on collision. I think Woody would agree with me.

I've never been in a head-on collision, but my thought is that I'd rather have the airbag go off in a 15mph collision than not deploy in a 40mph crash.

So the big downside to that happening is that if the insurance co denies me, I'll have to pay for a new airbag which could cost $1000+?

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~James
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Black '05 CRD Sport
L.O.S.T. # 068768
Rock Lizard Skink Sliders, Skid Row tranny skid, Wet Okole seat covers, Black Widow roof basket, front tow hooks, cargo/pet partition, all Amsoil

The way I read the quote is that the stock bumpers are designed to crumple to a certain extent BEFORE the airbag goes off (for low speed minor accidents). Then once a certain amount of crumpling has occurred (due to higher impact speed) the airbag with deploy when you need it.

It would appear that the after market bumpers that have not been tested to be airbag compliant reduce the amount of speed it takes to set off your airbag. By how much is anyone's guess, but as a hypothetical example, the airbag could be set off in a 5mph parking lot accident when they shouldn't have gone off. That's where you get to spend your money on buying a new one instead of having insurance pay for it.

It should still go off at higher speeds, so you would be safe there, but it may also go off at lower speeds when you don't need it causing you to shell out $$ for a new one.

I could be wrong, but that's how I read it.

N

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The beauty of a 4x4 is that you can get stuck at inaccessible places
=================================

2003 Liberty Sport
Blue w/ Gray trim
3.7L 5 Speed Manual
235/70/16 BFG MT's
65w Phillips fog light mod
AmsOil fluids end to end
SkidRow Front armor
Standard Frankenlift I & Al's U A-arms

ARB's are airbag complient,also the main supports have built in "crumple" zones.

Anyways our airbags sensors are inertia sensors not inpact sensors(genI airbags) so it doesn't really matter anyway.You can actually have the airbags go off in a emergency braking action if you get enough negitive "G's" without ever hitting anything,I have seen it before and no fault to the SRS system just got really good traction on a hard braking.

My understanding of the gen 1 air bags is similar to this. That there were 3 seperate sensors located in the front 1/2 of the vehicle. all were de activated untill you reached a speed of around 35 mph. Once that speed was reached and upon impact, only 2 of the 3 had to fire to activate the airbag.

The gen 2 are much more sofisticated. They messure the kenetic energy stored in the vehicle at the time of impact and determine the need for air bag deployment, or something like that.

Have you ever bounced a ball on a wooden deck and have the ball not bounce back as high as you would like, then do the same ball on concrete? that is the best example of the plastic vs. ALL steel, eliminated crumple zone aftermarket bumpers. They may be safer but the vehicles computer will inturpret the impact with a solid steel one as much more sever that it possibly is and thus fire the airbags prematurely.

Thus giving your insurance company the excuse, they love to find, to NOT pay for new ones.

Troy may be able to expand on the exact functioning but I think I am close to the basics here.

DONT get me wrong. I love the steel bumpers. The more steel I have infront of me out in this world the better. I was just giving everybody something to think about. Hell that's why I drive one of those deadly SUV's anyway and not a Geo Metro Hybrid piece of crap.

darn THE TORPEEDOS - FULL SPEED AHEAD!!!!!!!!!

Or to quote the former Personal Aid to the U.S. Senator Blutarski, Daniel Simpson Day, "RAMMING SPEED!!!!!!!!!"

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'07 Ltd 3.7L, Black, OME HD's, OME shocks, Mopar Skids, AEV Bridgers w/ TPMS, Kumho KL78's, ARB Bumper, KC 130 Watters, Warn M8000 Winch, Rock Lizard Gecko Roof Basket KC 150 watters, Cobra 75WSX, 3 ft FireFly, RL Super Step Skinks

Not KJ related- but this past week's ice storm I saw a a 06 honda accord hit a pole dead center which ended up totaled by the insurance co. and yet no airbag deployment,This happened on the road next to where I work by a fellow employee who was also injured ( not serious ), Makes me wonder ??

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2004 sport 3.7
OME coil lift.
Clevis lift.
Mopar skids.
5-speed manual.
235 70 17 Firestone destination AT'S on stock rims.
Gen 4.5 a-arms

Ooops, I'm the one that cracked that topic open, my bad. Was brought up on my nissan forum 2 years ago when I got my ARB

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'05 Black Renegade.
Frankenlifted
front/rear hitch with tow hook/d ring
custom Hella 500 cowl mounted offroad lights.
full tints
Ipod wired up
Possbily the first OIIIO Jeep license plater.
"Full" belly protection....who needs a gas tank skid anyways
Just need a bumper...
http://s180.photobucket.com/albums/x180 ... eRenegade/

I just wanted to ask the Q without hijacking someone else's bumper thread. It had been touched on a couple times and I was still a little foggy on it.

_________________
~James
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Black '05 CRD Sport
L.O.S.T. # 068768
Rock Lizard Skink Sliders, Skid Row tranny skid, Wet Okole seat covers, Black Widow roof basket, front tow hooks, cargo/pet partition, all Amsoil

Everybody is foggy on it, and that is what the insurance companies depend on.

It is a great discussion and everybody will have a different take on it. One big huge grey area that only allows the insurance companies the ability to decide what will happen.

A very good friend of mine is an automotive engineer and a hydralic engineer. Builds fleet trucks for cities and what not. everything from garbage trucks to snow plows and ambulabces...

When I got my KJ and got on here i was fired up about building a custom bumper for it like so many have done. I asked him if he would help. we started to look at designs and ideas and then suddenly, BOOM!!!!

he noticed the "Air Bag Compliance" issue and said STOP right there. He could no longer help me because of his insurance bond with his company. Once the Air bag issue came up he was forbidden from proceeding. Said that this is a big problem in the industry now (talikng about big trucks and fabrication in general) Said he could not touch my car now that that issue was brought up.

Maybe it is over reacting or maybe it is not that big of a problem, but Served as a warning to me. and should be a point of consideration for all.

Damned lawyers have us all under their thumbs.

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'07 Ltd 3.7L, Black, OME HD's, OME shocks, Mopar Skids, AEV Bridgers w/ TPMS, Kumho KL78's, ARB Bumper, KC 130 Watters, Warn M8000 Winch, Rock Lizard Gecko Roof Basket KC 150 watters, Cobra 75WSX, 3 ft FireFly, RL Super Step Skinks

if you want to know the physics behind it, I will attempt to explain:

it all goes back to F=ma. The airbag system monitors acceleration (a) at different points in the vehicle (i believe there are sensor up by the radiator supports and in the air bag control module on the transmission hump under the center console). the control module monitors the acceleration at all those points and determines the overall direction of the acceleration (or de-acceleration). when it determines the acceleration is too great for the given conditions (it looks at wheel speed, brakes applied and accelerometer readings to determine this) it fires the airbag(s) as needed for that particular velocity (speed AND direction....yes, it will fire only one airbag if it determines it only needs one) and the force of the airbag (there are 2 sqibs in each airbag...one low charge, one high charge. for maximum force, both are fired simultaniously).

so back to F=ma. the air bags go off when "a" exceeds a certain point. "m" is mass and the mass of the KJ is constant which leaves "F", or force. When "F" is increased, "a" will increase with it. Here's where the bumpers come in. Plastic bends easier than steel when a force is applied to it (assuming similar thicknesses of material and forces). Bending occurs when a material cannot react with enough force to keep whatever is applying the force from moving. (When you push on a wall, you exert a force of x lbs and the wall pushes back with that same amount of lbs...therefore neither of you move.) Because the steel bumper is stronger, in an impact it will push back on whatever you are hitting harder, in other words, with more force. Because there is more force being exerted to what you are hitting, there is more force slowing the mass down (your Libby) and therefore a greater acceleration (or de-acceleration....depends on your point of view).

Crumple zones work by taking the force you are applying to whatever you are hitting and doing work with some of it in addition to (de)accelerating the mass (by work i mean bending, twisting and tearing steel...it all takes force to do). That means there is less force being applied to slow you down and therefore less acceleration for the airbag module to read.

did that help?

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'03 Liberty w/3.7L & 45FRE Tranny
Revetek 2" Lift & JBA Gen 5 A-arms
Maxxis Buckshot XMT Mudders 31x10.5 on Soft 8's
Jet Stage 2 Chip : '07 Air Intake
Relocated IAT Sensor : '05 HVAC Controls
Front Hitch : EVIC from '01 GC : Custom Rock Rails
Transgo Shift Reprogramming Kit
KC Driving Lights & Aux Backup Lights
.......all GONE!

I have a brain ache.

I am not sure we need a physics lesson. Just keep in mind that what we put on our KJ's can and might well effect not only the handeling, looks and cost of it but may also have an effect on our wallets down the road.

Tim welcome back from the honeymoon.

So how was that marital bliss?

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'07 Ltd 3.7L, Black, OME HD's, OME shocks, Mopar Skids, AEV Bridgers w/ TPMS, Kumho KL78's, ARB Bumper, KC 130 Watters, Warn M8000 Winch, Rock Lizard Gecko Roof Basket KC 150 watters, Cobra 75WSX, 3 ft FireFly, RL Super Step Skinks