Another one of my weird ideas. Any engineers reading this?

You guys are over thinking this. Your probility of dieing (in the USA) from a drug overdose is higher than dieing in a car crash (CMC or not).

 

I wonder how they are able to reinforce it and protect the vital components of the vehicle will still making it crumble the same as the factory bumper. Seems like they are opposing goals.

 

I definitely understand where you're coming from, and agree with you about the safety engineering and testing of aftermarket bumpers. That said, one thing worth mentioning is that there are multiple crump zones built into your Tacoma and not just your front bumper.

The pedestrian aspect of having an aftermarket bumper, eh, I'm much less concerned about that. There are endless factors that are involved in auto-pedestrian collisions, and I'm not sure how much of an effect an aftermarket bumper will have in such a scenario in the following sense: An organic body (human or animal) hit by a solid object weighing a couple thousand pounds or more that was traveling at X speed is going to be significantly traumatic in of itself.

 

I think that part is just for the airbag deployment, but you would know better than me...

Speaking of, I recommended you guys to a dude I met the other day with a 4th gen 4runner. He was looking for a rear plate bumper.

 

I’ll play. In a front end crash the motor is supposed to go down through the bottom of the vehicle and not through the cab. How does my IFS, and soon to arrive mid skid effect this? Also my sliders noticeably stiffens the frame, does this ever become a liability?

All in all I default to NASCAR “roll cages” as my model. My belief is more steel is better. This is why I drive a 4500lb vehicle and not a Civic. Side note I will still take your Mini Cooper (gratis) off your hands since its unsafe.

 

Being hit or being deflected? Big difference. OEM bumpers look like they would deflect an object more so than "off road" ones. Therefore the body would not have to absorb the whole force.

 

Perhaps. Its something worth thinking about. I find it difficult to think that pick-ups with the "big rig" style front ends and overall height of the vehicle itself does much in the way of deflecting anything, but you could be right.

Again, there are a whole lot of factors involved with auto-pedestrian collisions and when considering the "why" and the "how" of such an event, I'm really doubtful that the front bumper style or material is going to matter a whole lot unless you have something straight out of Mad Max. But it could.

 

Lot of good info here on what is being done.

https://www.edmunds.com/car-safety/protecting-pedestrians-through-vehicle-design.html

 

Honestly, I don't. I just ask a lot of annoying questions.

Awesome. Thank you so much.

 

Informative read.

Interesting tidbit from that article:

"For vehicles in Europe and Asia (where there are many more pedestrian collisions and governmental standards regulating them), bumpers are designed with larger crush space and with different supports for the plastic bumper cover in order to reduce leg injury. Unfortunately, these "softer" bumpers don't perform well in the 5-mph bumper test conducted by the Insurance Institute for Highway Safety (IIHS) to assess repair costs, so they generally aren't used on vehicles in the U.S."

 

I read the this whole thread. I'm an engineer. I work in IT, but I had to take Physics I and II at a university considered one of the top 10 in the USA, so I understand enough about inelastic collisions and Newton's laws to have a decent answer here. Key points bold for emphasis since this got long.

Going back to the original question @Rujack asked: "how much the impact profile might be preserved in a front collision in a Tacoma that has a plate bumper installed, with the stock crash bar mounted on the front of it" -- this is difficult to take a scientific approach on using statistical-based analysis. There simply aren't statistics on probabilities of a front-end collisions to the level of granularity to be useful. https://crashstats.nhtsa.dot.gov/Api/Public/ViewPublication/811059 page 28 has some great statistics though.

I have a few considerations:

• Directly answering the question; ANY addition of more crumple zone means an increase in mass and volume in a collision and an, if in a location that will impact in a collision, an increase in "crumple zone."
  • Airbags utilize an accelerometer that detect rapid inertia changes that occur in a crash.
  • Adding a plate bumper AND the stock crash bar will add mass and volume, adding inelasticity to collisions and reducing the probability of a rapid inertia change. This decreases both the inertia change on the passengers and the likelihood of the airbags deploying.
  • More mass also means more relative momentum in an accident. This is advantageous to you, as a greater impact is therefore required to affect the vehicle. This is a consideration for driving a larger, heavier vehicle for safety. If you're genuinely concerned, drive the largest and heaviest vehicle you can reasonably afford.

Adding just a plate bumper WILL affect the dynamics of a collision due to the physics of steel versus aluminum. As a primer, a perfectly elastic collision is a perfect bounce with no deformity -- both objects remain intact and deflect fully. An inelastic collision is not a complete bounce; a portion of the velocities of the two objects are absorbed by deforming the objects. Part of the impact remains deflection, but the rest is absorbed by the two objects shearing or deforming as a result of the impact. Recall the stock crash bar is aluminum, whereas a bumper is typically steel of a larger thickness. Aluminum is far more malleable, or likely to bend, than steel, meaning the collision will be more likely to be inelastic.

For the below, assume you are colliding with the rear end of another car:

• At low speeds, comparing options:
  • Stock low speed collision - This option performs worse:
    • The factory aluminum crash bar effectively deforms, soaking up the damage and preventing any chassis damage.
      
    • The airbags are less likely to go off, because the inelasticity of the collision deforms and completely destroys the crash bar.
      
    • The front end needs replaced, but the passengers are glad to be unphased.
      
    • The car you rear-ended got a good bump, but it's just a bumper issue more than anything else.
  • Aftermarket bumper low speed collision - This option performs better:
    • The steel plate bumper remains stiff, transmitting the energy of the collision directly to the vehicle.
      
    • The airbags are unlikely to go off at this speed, and the collision is more or less elastic for the truck. There's no damage at all to the truck, which is really why you have this bumper for offroading anyways.
      
    • The front end is fine, and the passengers got bounced up a bit.
      
    • The car you rear-ended is surprisingly damaged, because your front end didn't deform at all.
• At medium speeds, comparing options:
  • Stock medium speed collision - This will vary:
    • The factory aluminum crash bar was completely destroyed and the chassis experienced damage.
    • The airbags are fairly likely to go off, the collision is a strong hit and there is little deflection.
    • The truck may be totalled. It's hard to tell. The passengers are probably fine, if a bit shaken up.
      
    • The car you rear-ended is pretty messed up. You both will need rental cars.
  • With aftermarket bumper, this gets complicated. If the truck is square on with the impact (think hitting a brick wall), then the collision is forced to be MORE inelastic and the collision is worse. If the truck is not square with the impact OR the impact is with a substantially more inelastic object, deflection or more damage to the other, more inelastic, object occurs and the collision is relatively elastic and much better:
    • The steel bumper is about the same stiffness as the chassis, so either both bumper and frame are bent from a square inelastic collision, the vehicle in front of you soaks up almost the entire collision and your truck remains stout, or your truck deflects almost completely.
      
    • The airbags will either definitely go off from the square and jarring impact, or the impact is a bounce as far as the truck is concerned. In the former, the truck is definitely totaled (doors won't open from impulse transmitting back). In the latter, there's basically no damage, but the passengers will be more likely to get whiplash.
      
    • The truck either is totaled from a bent frame (inelastic collision) or mostly unharmed (elastic collision).
    • The car you rear-ended is absolutely proper fucked either way. Since your front end is rigid, way more of the impact is absorbed by the inelastic rear end of the car in front of you. You do have good insurance, right?
• At high speeds, comparing options (they're really close to the same):
  • Stock:
    • The factory aluminum crash bar is destroyed, the frame bends and soaks up the impact at the crumple zones around the engine bay. The engine drops down, and the passenger compartment is pushed upwards, as designed, to lessen impact.
    • The airbags go off.
    • The truck is totaled. The passengers were wearing their seatbelts and hit airbags, so they are injured, but will live.
    • The car you rear-ended is totaled, just like you.
  • With aftermarket bumper:
    • The bumper extends your crumple zone. It is hooked to the frame, both bumper and frame soak up the impact at crumple zones. The engine drops down, and the passenger compartment is pushed upwards, as designed, to lessen impact.
    • The airbags go off.
    • The truck is totaled. The passengers were wearing their seatbelts and hit airbags, so they are injured, but will live.
    • The car you rear-ended is totalled, just like you. But, your extra mass and rigidity give you more elasticity in the collision. The other vehicle is worse off than you, or if you are hitting a larger vehicle, you impart more relative momentum and are still better off than you would have been with less mass (Newton's 2nd law at work)

Nothing beats mass in a collision. I have an aftermarket streamline bumper that was only $500, and would have bought the full ARB bumper if I had the funds. It adds more crumple zone and more mass, both of which add safety. I spent way more on a heavy full-plate rear -- I drive defensively and don't really speed, so I'm far more likely to get rear-ended.


If anything else, if you're concerned about safety, this is a GREAT quick read: https://crashstats.nhtsa.dot.gov/Api/Public/ViewPublication/812451 and this is even better: https://crashstats.nhtsa.dot.gov/Api/Public/ViewPublication/812013 A tl;dr:

1. Wear your seatbelt (duh)
2. DO NOT DRINK AND DRIVE.
   
3. DO NOT SPEED.

Your risk of fatality has now more than halved, without even going into the physics of bumpers.


Regardless, I'm strongly of the belief that a well-designed plate bumper will do nothing but help your case with a collision with another car, animal, or pedestrian, with little exception. That exception is at moderate speeds, where the stiffness of a plate bumper COULD cause an airbag deployment where one normally wouldn't occur due to less absorption and therefore more jarring of an impact. Either way this impact is non-fatal with both configurations. Therefore, the benefits outweigh the risks. I don't speed, I don't drink and drive, I don't text and drive, so my chance of rear-ending someone is low. However, I can't avoid the risk of t-boning someone running a red light or the risk of deer in our area, and in both of those cases, having a bumper like this is advantageous. If you can stomach the look of a massive and relatively ugly plate bumper plus the cost, I think it's a worthwhile addition.

 

Nicely done sir. My moderately rated university physics education says you get an A+.

 

Lol when I write here I keep it as much as possible in layman's terms! 1/2 mv sq ftw!

 

Yeah and I think they just threw the word “tirelessly” in here sort of haphazardly. It’s not like they were building a fucking pyramid in Egypt.

 

haha sounds like they just hired a shitty copywriter. Still, an impressive amount of research and testing.

 

So again. In my case I opted for an aluminum plate front bumper. My assumption is that given the properties of aluminum I am getting most off the benefits from having a beefier f not bumper and still having some cushion being that the aluminum will deform more than steel. Am I correct in my assumption or am I processing this incorrectly.? And mahalo for your in-depth explanation.

 

Depends on how hard you are smacking the other object. Most materials are strain rate dependent, so the faster you hit them, the stiffer/harder they behave until they fail.

 

Take a look at this:
https://www.tacomaworld.com/threads...per-with-damage-georgia.559570/#post-18287229

Not sure how fast the truck was traveling, but the bumper took the hit on the Tacoma and looks like the member was able to walk, If there was anyone in the white car that took the energy of the accident they were probably hurt and this could have been worse with more speed.

 

Another thing to consider is the shape of most plate bumpers. If you rear end a car at higher rate of speed, you are most likely going up and over the rear end of the vehicle causing more damage.

 

Is that why we should have good skid plates?