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Aluminum Bumper Safety

Hayseed_JLUR

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One important functionality of the bumpers is protection on the road.

Does anyone have real world knowledge on how the aluminum bumpers perform in an road accident? Especially compared to their steel counterparts?
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xeon

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As a prior airbag test engineer....I can tell you that changing your bumper from the factory provided bumper ...regardless of steel or any other material will change the crash characteristics of the vehicle. What this means is your front air bags will deploy at a non optimized time during a crash event. I am not saying they wont deploy...it just wont be as the engineer designed them to. An aluminum bumper will be softer and crush easier than a steel bumper. This is good news in the science of keeping your brains from splattering against the inside of your skull. Energy will be absorbed by the aluminum bumper better than steel. But there is a chance...the airbag may fire late or may require a higher speed to fire the air bag, in which case the aluminum might be a bad thing. I don't believe any one is doing aftermarket airbag testing of bumpers of jeeps. My other guess is JEEP FCA recognizes this too and has some allowances for different bumper types in their algorithm to fire the air bags. So you are probably going to be okay either way on the road. As far as off road and general bumper abuse....I will let others chime in on that. However I will say...with my background...i went for steel. As far as size stubby or wide... the steel factory bumpers are really a stubby bumper with bolt on wings...that wont help much in a high speed accident but do offer some safety during non air bag deployment events. Not sure any of this helps or not but I guess the forums will continue to show us accidents and we will find out in real world test cases eventually.
 

oceanblue2019

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As a prior airbag test engineer....I can tell you that changing your bumper from the factory provided bumper ...regardless of steel or any other material will change the crash characteristics of the vehicle. What this means is your front air bags will deploy at a non optimized time during a crash event. I am not saying they wont deploy...it just wont be as the engineer designed them to. An aluminum bumper will be softer and crush easier than a steel bumper. This is good news in the science of keeping your brains from splattering against the inside of your skull. Energy will be absorbed by the aluminum bumper better than steel. But there is a chance...the airbag may fire late or may require a higher speed to fire the air bag, in which case the aluminum might be a bad thing. I don't believe any one is doing aftermarket airbag testing of bumpers of jeeps. My other guess is JEEP FCA recognizes this too and has some allowances for different bumper types in their algorithm to fire the air bags. So you are probably going to be okay either way on the road. As far as off road and general bumper abuse....I will let others chime in on that. However I will say...with my background...i went for steel. As far as size stubby or wide... the steel factory bumpers are really a stubby bumper with bolt on wings...that wont help much in a high speed accident but do offer some safety during non air bag deployment events. Not sure any of this helps or not but I guess the forums will continue to show us accidents and we will find out in real world test cases eventually.
Nice response - I appreciate the detail. Any thought on Jeep with steel bumpers versus the majority of the other vehicles on the road with plastic bumpers from a safety perspective?
 

MtCamper

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Shortly after I installed a RodkHard aluminum bumper on my Jeep, I hit a deer. By the time I hit it I would guess Is was still traveling at about 40 mph. Deer was totaled, bumper needed a good wash to remove hair and body fluids. It was a bit of a bit of an oblique strike and airbags did not trigger. The jeep bumper sits high enough that the deer was thrown ahead of the vehicle rather than under or over. No sheetmetal damage.
 

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Nice response - I appreciate the detail. Any thought on Jeep with steel bumpers versus the majority of the other vehicles on the road with plastic bumpers from a safety perspective?
Don't plastic bumpers have a metal bumper under them?
 

MtCamper

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I've replaced both the plastic bumpers that came with my Jeep. Lots of screws, clips and plastic to get to fog lamp harness and back up sensors. Very little metal in either one especially in the rear one. I just can't imagine either one holding up for even moderate off roading.
 

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I was shocked at how thin the metal was behind the plastic bumper. It's just thin sheetmetal. The frame rails are going to be doing most of the impact protection, the bumper it's self is mostly cosmetic.
 

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Shortly after I installed a RodkHard aluminum bumper on my Jeep, I hit a deer. By the time I hit it I would guess Is was still traveling at about 40 mph. Deer was totaled, bumper needed a good wash to remove hair and body fluids. It was a bit of a bit of an oblique strike and airbags did not trigger. The jeep bumper sits high enough that the deer was thrown ahead of the vehicle rather than under or over. No sheetmetal damage.
That's good testimony! I don't want to add weight, but was leaning steel...until now.
 

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xeon

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Jeeps Plastic bumpers..... the name really doesn't state what they are made of but what the outer shell is. Much like a modern car with a plastic covering to hide the real bumper inside. The important thing is not the outer material but the "system" defined as the covering, the foam core, the metal structure beneath and how it's attached to the JEEP to provide the impact resistance during a crash event to allow the airbag to go off. In a crash event... you airbag needs to go off.. you want your bumper to crumple to absorb the impact. So steel or plastic...both accomplish the same thing. Heres the rub. I believe I have only seen the NHTSA test 2018/2019 Wranglers with "plastic" bumpers and they did really well....and well seen plenty of pics on the forum of JEEPS with steel after significant impacts and they did well too.

So whats the real difference - steel, aluminum, "plastic"....its all in the low speed things where you will see a difference.


To break this down..... lets consider a 5 MPH event of hitting a steel bollard / parking pole - airbags will not deploy but it will be a nice thump if you aren't expecting it. By design a car's plastic bumper cover will collapse, probably pop loose from its plastic fasteners and leave a potential indentation the plastic. Under neath, the foam core will flatten and you will probably impact the steel bumper under neath but will not sustain any damage to your fenders, trunk, hood etc. The 5 MPH test is to have a minimal cost damage amount and minimal impact to other components outside the bumper system.

So in a car - expect to pay $1500 or so to pop out a bumper and potentially repaint it.

JEEP with a plastic bumper.....well - its going to get a pinch/crease/dent in the plastic and some substantial bowing and not look so great unless you just like a rustic looking jeep with scars but you could move on and not worry about it. Haven't priced out a new "plastic bumper" but i imagine its going to be similar to the above.

Jeep with aluminum bumper - well...its going to leave a mark. Those darn parking poles are nasty business. Depending on the shape of the bumper I would expect some indentation but the pole to bend over a bit as well...making that indentation only a fraction of an inch or so. The impact will seem worse to the drive than if he hit it with a "plastic" bumper.

Jeep with Steel bumper - well...its going to leave a mark too. Probably not as deep as the aluminum but the impact will be more violent and the pole will be taking most of the damage along with your brain slushing in your head momentarily.

The plastic bumpers are designed to absorb energy and protect our noggin and does so even at lower speeds. Once you get into aluminum and steel. You sacrifice low speed absorption for ruggedness and hitting stuff like well... deer or elves, or damn...don't hit Santa without impacting the physical characteristics of the bumper.

So...yes...all plastic bumpers have metal under or inside them. And yes they are great bumpers for most every driver. Except those that obviously want to be a bit more adventures at slow speeds without having to worry about bumper replacement when they rub up against a rock, tree or other object.

Again for me....I choose steel. Low impacts - I just want to win and not worry about what hit me or what I hit and I don't want to have to worry about shelling out money each time a rock jumps out in front of my JEEP. Then again...its one less thing to cover with 303 protectant.

The tradeoffs are for the owner to decide what its best for them especially as cost plays a role too.
 

xeon

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Shortly after I installed a RodkHard aluminum bumper on my Jeep, I hit a deer. By the time I hit it I would guess Is was still traveling at about 40 mph. Deer was totaled, bumper needed a good wash to remove hair and body fluids. It was a bit of a bit of an oblique strike and airbags did not trigger. The jeep bumper sits high enough that the deer was thrown ahead of the vehicle rather than under or over. No sheetmetal damage.

The bumper on JEEPs are specifically designed to provide the correct crash pulse characteristic needed to deploy the air bag under the specific conditions that warrant an air bag deployment. This goes for steel or plastic etc.

Hitting a deer is actually not that bad of an impact with respect to the crash sensors in the vehicle, which is why the airbags did not go off. I am not saying in any way that the accident was not bad....or dangerous...glad you are ok.
 

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The bumper assembly I removed from my JLUS didn't have sensors in it. I don't know for a fact but I think perhaps Jeep uses an accelerometer for airbag deployment.
 

xeon

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The bumper assembly I removed from my JLUS didn't have sensors in it. I don't know for a fact but I think perhaps Jeep uses an accelerometer for airbag deployment.

Air bag individual sensors are something you might have found in the 90's on many cars. Initial system consisted of 4 to five sensors located in the engine compartment, passenger compartment and trunk areas. They never existed in the bumpers. The sensor has to have time to react to the crash pulse so you want them further back in the vehicle so it can recognize the accident before being destroyed. Initial sensors were mechanical roller actuators or ball cylinder systems, then came gas dampening sensors. At the time i left my career in airbags sensor tech...they had moved to an electronic consolidated system with radar sensing to anticipate oncoming collision events. The goal was single black box if you will. Accelerometers do measure the same pulses as a crash sensor but are far more fragile and expensive to be placed in a production vehicle. But the general idea is the same.

You definitely do not have to worry about sensors in your bumpers though. I haven't looked at a diagram yet but I would imagine you would find the main module under the dash somewhere in our JEEPS.
 

EJA

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Vehicles at one time had a single point crash sensor but at least for the company I worked for we went back to front sensors (2) and one rear sensor. The deployment calibration was based off of the signals of all 3 sensors for a crash event.

I think people are misunderstanding the purpose of a bumper. Bumpers in vehicles are designed to protect the vehicle from extensive damage in low speed events (for a Jeep this may not apply, I donā€™t know). For crash, their purpose is to transfer load to the rails, especially if the rails are not engaged directly. Their intent is not to ā€œabsorbā€ energy in a crash scenario.

I would argue the deployment calibration is based on the vehicle design, not the other way around. I expect Jeep calibrated for both the plastic and steel bumper, at least for certain conditions.

I had the steel bumpers because I didnā€™t want to effect the calibration/ deployment but since I was going to add a winch I figured Iā€™m messing it up anyway and went with aftermarket which is what I really wanted. I figure Iā€™ll get an earlier deploy time which for most cases should be better. Even with a stock bumper you are going to effect the deployment when you add a winch plate and a winch.
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