Safety of steel bumpers

[Smalldog]

I currently drive a JKU with steel bumpers (AEV as part of the Backcountry Package) and wonder about the degree to which the lack of a crumpling bumper makes the Jeep even less safe (current safety rating, I think, is just 1 star). I suppose with a steel bumper any impact will transfer all kinetic energy right to the driver. Anyone know about the safety differences between the two in a high-speed impact.

Low impact seems ideal for steel bumpers, but I worry more about the hazardous impacts.

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[ZackDanger]

I currently drive a JKU with steel bumpers (AEV as part of the Backcountry Package) and wonder about the degree to which the lack of a crumpling bumper makes the Jeep even less safe (current safety rating, I think, is just 1 star). I suppose with a steel bumper any impact will transfer all kinetic energy right to the driver. Anyone know about the safety differences between the two in a high-speed impact.

Low impact seems ideal for steel bumpers, but I worry more about the hazardous impacts.

Your AEV bumper should have crumple "pods" that stick out in the front of it. My ARB does... since the bumper obviously bolts directly to the frame.

As far as the Bronco goes, I wonder if the crumple portion is between the bumper and the frame.

 

[AzScorpion]

Ford has crash bars on the front and rear behind the bumper.

 

[mneblett]

I currently drive a JKU with steel bumpers (AEV as part of the Backcountry Package) and wonder about the degree to which the lack of a crumpling bumper makes the Jeep even less safe (current safety rating, I think, is just 1 star). I suppose with a steel bumper any impact will transfer all kinetic energy right to the driver. Anyone know about the safety differences between the two in a high-speed impact.

Low impact seems ideal for steel bumpers, but I worry more about the hazardous impacts.

In a high speed impact? It will be like the bumper isn't even there -- you're going to have passenger compartment intrusion anyways, given the Wrangler's design.

In a lower speed impact, the steel bumper should still yield, perhaps to a lesser extent, but the rest of the energy absorbing structure between the bumper and the cabin will be doing its job.

And even if the steel bumper is perfectly rigid, the end result would be the same as a plastic bumper: little/no energy absorption at the bumper. At best, the steel bumper would better link the left and right side crush zones together, spreading out the impact energy a bit.

 

[Efthreeoh]

All cars have steel or aluminum bumpers underneath the plastic cover. The plastic cover is just for aerodynamics and styling. All the work to distribute and manage crash energy is done under the plastic cover.

Some cars do have foam energy absorption material under the plastic cover along with the metallic infrastructure, but it's for low speed impact to lessen damage.

 

[Smalldog]

In a high speed impact? It will be like the bumper isn't even there -- you're going to have passenger compartment intrusion anyways, given the Wrangler's design.

In a lower speed impact, the steel bumper should still yield, perhaps to a lesser extent, but the rest of the energy absorbing structure between the bumper and the cabin will be doing its job.

And even if the steel bumper is perfectly rigid, the end result would be the same as a plastic bumper: little/no energy absorption at the bumper. At best, the steel bumper would better link the left and right side crush zones together, spreading out the impact energy a bit.

That is reassuring to hear... thanks

 

[AzScorpion]

Bronco crash bars.

 

[wjfawb0 [hacked account]]

If you look at the front frame on a wrangler, it has crush cans built in just after the bumper mounts. The stock bumper is all plastic with some thin metal to help it keep shape and metal mounting plates where it bolts to the frame. I replaced my plastic bumper after a bedliner was punted across the interstate and tore my plastic bumper. I bought a $300 chinese steel bumper that I have used to push boulders and bash other rocks. The AEV stuff is nice, but too expensive to be touching up from time to time if you actually go offroad. I want to replace my rear bumper with a steel warn bumper, but I don't want to add any more weight to my jeep. It is already over 4400lbs for a two door rubicon.

 

[mneblett]

Bronco crash bars.

Good pics. The OP should understand that these are but small parts of the overall collision energy absorption system design. The primary purpose of these bars is to control how the front wheel is deflected during a crash, specifically to try to steer the wheel away from the passenger compartment. There's much more structure throughout the front half of the vehicle in the crash energy management design.

 

[beachman101]

"hard" solid steel cars were only dangerous in the 50s when all the other cars on the road were build like tanks

so unless you plan into crashing into a tree or wall , the more stiff your car is the safer it is running into soft cars

just not so good for the occupant of the other vehicle

 

[Smalldog]

Good pics. The OP should understand that these are but small parts of the overall collision energy absorption system design. The primary purpose of these bars is to control how the front wheel is deflected during a crash, specifically to try to steer the wheel away from the passenger compartment. There's much more structure throughs the front half of the vehicle in the crash energy management design.

I do now... this has been very helpful,
Sincerely,
The OP

 

[AcesandEights]

The bumper doesn't really have anything to do with how crashworthy the vehicle is. Steel or plastic, the way the energy is transferred is built into the vehicle throughout. The entire vehicle is engineered to both absorb, and displace, energy away from the occupants.

A plastic bumper is just a sheet of plastic shaped to be aesthetically pleasing. There is a piece of Styrofoam under it that is built to withstand a 2 mph - 5 mph impact. It is broken in the most insignificant of impacts and is often broken without you knowing it. The energy it displaces is minimal. It is attached to a steel crossbeam which is mounted to crumple zones.

A steel bumper is only a piece of steel that has been formed to be aesthetically pleasing. Instead of Styrofoam, it is mounted to "rails" and a crossbeam that have crumple zones (same as the plastic bumper). Those crumple zones are designed to "absorb" the energy.

The design of the frame/unibody moves or transfers and displaces the energy. The curves you see in a body on frame are designed to bend at different rates. You have crumple zones where the bumpers mount, at the ends. You then have strategically designed and places/zones meant to bend. If you're interested, you can look, follow, from the end of the vehicle to the passenger compartment and see bends, holes, and dimples in the frame or unibody. These are all designed as separate points in the overall structure that are going to absorb or displace the energy of an impact.

If you spend some time looking at a vehicle that has been in an accident, you can literally "follow" the damage from impact to where it has been displaced/absorbed enough that it stops travelling through the vehicle. In minor impacts you'll see the damage at the impact site and one or two "dimpled" areas back. In more severe accidents you'll follow it to the firewall or if it is bad enough, into the passenger compartments. Even your windshield is designed as a structural component of the vehicle.

All of this is designed to protect the passengers and minimize the transfer of energy to the occupants. In addition, active safety measures are also in place, namely airbags. They will deploy even when the transfer of energy is minimal to the occupant, even when the "crumple zones" don't reach the passenger compartment.

No joke, if you have a chance to go to a wrecking yard and have someone point out the damage it'll be eye opening. Someone trained in damage analysis (ASE Certificate B6) can, as I said above, literally follow the transfer of energy from the damage and impact and show you the energy transfer throughout the vehicle. It's kind of cool in a geeky sort of way.

As to your concern, plastic or steel, the bumper isn't going to make a difference on the felt energy/impact in the passenger compartment.

 

[Smalldog]

The bumper doesn't really have anything to do with how crashworthy the vehicle is. Steel or plastic, the way the energy is transferred is built into the vehicle throughout. The entire vehicle is engineered to both absorb, and displace, energy away from the occupants.

A plastic bumper is just a sheet of plastic shaped to be aesthetically pleasing. There is a piece of Styrofoam under it that is built to withstand a 2 mph - 5 mph impact. It is broken in the most insignificant of impacts and is often broken without you knowing it. The energy it displaces is minimal. It is attached to a steel crossbeam which is mounted to crumple zones.

A steel bumper is only a piece of steel that has been formed to be aesthetically pleasing. Instead of Styrofoam, it is mounted to "rails" and a crossbeam that have crumple zones (same as the plastic bumper). Those crumple zones are designed to "absorb" the energy.

The design of the frame/unibody moves or transfers and displaces the energy. The curves you see in a body on frame are designed to bend at different rates. You have crumple zones where the bumpers mount, at the ends. You then have strategically designed and places/zones meant to bend. If you're interested, you can look, follow, from the end of the vehicle to the passenger compartment and see bends, holes, and dimples in the frame or unibody. These are all designed as separate points in the overall structure that are going to absorb or displace the energy of an impact.

If you spend some time looking at a vehicle that has been in an accident, you can literally "follow" the damage from impact to where it has been displaced/absorbed enough that it stops travelling through the vehicle. In minor impacts you'll see the damage at the impact site and one or two "dimpled" areas back. In more severe accidents you'll follow it to the firewall or if it is bad enough, into the passenger compartments. Even your windshield is designed as a structural component of the vehicle.

All of this is designed to protect the passengers and minimize the transfer of energy to the occupants. In addition, active safety measures are also in place, namely airbags. They will deploy even when the transfer of energy is minimal to the occupant, even when the "crumple zones" don't reach the passenger compartment.

No joke, if you have a chance to go to a wrecking yard and have someone point out the damage it'll be eye opening. Someone trained in damage analysis (ASE Certificate B6) can, as I said above, literally follow the transfer of energy from the damage and impact and show you the energy transfer throughout the vehicle. It's kind of cool in a geeky sort of way.

As to your concern, plastic or steel, the bumper isn't going to make a difference on the felt energy/impact in the passenger compartment.

Thank you .... best answer yet!

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