CBI vs. ARB bumpers

Yep the OEM 3rd gen bumper is the same (aluminum bumper reinforcement).. I still am not mounting my winch bumper to an aluminum pedestal.. if you want to by all means be my guest but I use my winch and don’t trust it . .

 

Its not the same place anymore sadly. Full of triggerd hipsters, homelss, druggies, and criminals. Not all of course, but enough to make it not woth staying. Besides... the house i grew up in near Marina High, we bought in 93 for $179k. Last June we sold for $710k and it was nothing special by any means. Gotta be rich to own, or you will rent your enitre life now.

 

Don't know about the 3rd gen but in the 2nd gen the aluminum crash bar is removed with an ARB. They have a steel subframe you mount to the truck and the bumper hangs from it. It seems better thought out and more substantial than the crush cans they used in the 1st gen.

I've winched plenty hard on this combination and haven't seen any evidence of it yielding. Gaps are still the same between the bumper and fender the frame, bumper and skid plates are all still in alignment so bolts don't hang up trying to remove anything.

One recently was a fairly harsh one, had to pull myself up the side-by-side line on Top Of The World out in Moab, after making the uphill Z turn I couldn't back down it without digging in my rear bumper and without a front locker it was going to take a lot of rock stacking.

That ended up being a 45° up angle lifting the front up a bumper-high step. If the mount was going to tweak that was gonna do it. My winch is an XD9000 and the load was completely hung on on the top roller lifting the tires up. I was able to unwind two layers off the drum to the anchoring truck, so that's about 6,500 lbs max pull and the winch was definitely working to get it done.

 

Let me add this question then: does everything you can crash into have the same impartation of forces on your vehicle?

Does the airbag system know whether you hit a concrete pillar, or a pillow covered concrete pillar, or a semi truck? All of those things will show different shock graphs.

With the 39 million different things you can crash into, Id bet anything changing your own bumper stiffness matters a whopping "who cares".

I'll further raise a somewhat common occurance: now that you have a 1-200lb bumper (aluminum crash can or not), you've increased the momentum of your vehicle significantly. When you hit another moving object, you will slow down less than you otherwise would have stock. Does your airbag system know that?

Id almost argue that the fact you decelerate less (higher momentum) offsets the fact that the shock impulse travels a millifraction faster through the first foot of your vehicle. Not to mention that I'd also heavily bet any anything fluid (your body) reacts orders of magnitude slower to the shock than solids (airbag system, frame, seat belt, that anvil you had in the backseat), so again, won't frikkin matter.


Edit: the who cares/won't matter comments while technically false, are philosophically true. I'd highly prefer my dryer stops eating socks, but on the scale of how will it affect my retirement savings... Who cares/won't matter.

 

I can only speculate since I am not an airbag designer. Also the answer can't be generalized because airbags have evolved a great deal over the 30-some years they've been around. So the way a 1995 Tacoma airbag works is significantly different than a 2020 Tacoma.

My thinking is the early airbags assumed a very specific profile so the sensor response and the airbag construction and squib worked for a worst case, probably a head-on high speed sort of crash. Changing the bumper on those is probably the most likely to significantly change the timing since any intelligence is limited and it's probably just a damped switch and one-size-fits-all trigger (Google Rolamite acceleration switch, which is how the really early ones worked).

On the later ones the profile is built in software so what you're hitting is immaterial it's just looking for rate of change, e.g. a multi-term equation describing what inputs are required to generate an output. These days there may be several potential outputs varying in magnitude and time.

So the answer is yes, probably it does know implicitly.

Yes it does. Vehicles now know your velocity, rate of change (acceleration or deceleration) in velocity and direction. So your momentum is known through the accelerometer and yaw rate sensor data.

That's why my belief is a brand new truck will probably adjust more readily to a rigid bumper better than one 5 or 10 or 20 years ago that required more assumption be made to generate a response they want. But I do not have any idea how much the algorithm can adjust and the resulting safety consequences. Toyota may know the impact and ARB to meet Australian vehicle rules has to test to demonstrate their bumper does not change the response from the factory. I don't question the quality of the small fab shops at all as far as being solid off road bumpers. I'm just thinking aloud about the on road implications. It might be minimal or it might be better if we were pulling the airbag fuse, I really don't know.

The two airbag sensors are located at the front bib so what happens immediately behind the bumper is just as important as what the yaw rate sensor under the seat is doing. There's also a seat position for how close you are and occupant weight sensor that feeds information to the airbag ECU. So it's trying to determine a lot of things here.

Some study of this was done very early on. First generation airbags typically inflated very quickly, in one study at Tulane they assumed normal being 37.5 milliseconds after impact. If someone's not familiar with units that's 37.5 thousands of a second and if you want to compare it to something the term "blink of an eye" means about 300 milliseconds. They delayed the inflation to 100 milliseconds after impact. Still 3 times faster than it takes you to blink. But this change was found to increase the risk of neck injury by 5 times. So it was too slow. So yes milliseconds do matter. In this particular test the *least* risk of neck injury (done at 17 MPH, so it wasn't an NHTSA or IIHS test) was with no airbag at all, too.

http://www.tulane.edu/~sbc2003/pdfdocs/0139.PDF

There's engineers who's whole career is spent studying the specifics of crash response and I most definitely do not claim to know 1/1000th of it. They can stage airbags to inflate and deflate over longer periods, adjust how much volume is inflated, change the shape with tethers, lots of things. How much changing the bumper affects, without modeling and experimenting it is impossible to say.

 

@Alnmike, you might like this white paper I found "Air Bag Deployment Critieria" by a couple of engineers at joint called Institute of Risk & Safety Analyses.

They mention a couple of case studies where there could have been sufficient values to trigger but the airbags did not deploy. For example a Chevy SUV hitting a Harley motorcycle or a Corvette running over a bunch of shrubs and street signs. The large difference in masses (e.g. transfer of momentum) did keep the collision below either the maximum rate of change in velocity or force required for an airbag trigger.

But they also mention vehicle stiffness having an effect on response and a rigid bumper would be part of that equation. They even specifically mention a Prius vs. Ford Focus because apparently the Prius front end is significantly more rigid than the Ford.

 

The answer almost has to be generalized, because it's so complex. I'm not saying Arb sucks or anything, but there's no way they accounted for more than the specific check boxes they were required to. If they did more, I'd be simply amazed and would never buy another product if I could, but I just haven't read anything besides "airbag timing". Which, while impressive enough, doesnt account for the other complex intermingling variables (or if keeping the exact timing is even beneficial with an extra 150# on your bumper).

I tend to subscribe to the thought that the pieces that have sensors on them are the important bits. Not having taken off my bumper (yet), I've been hearing that the sensors are behind the crush bar. I just have a very hard time believing that the bar actually does anything in a high speed crash, the percentage of energy absorbed by it is absolutely miniscule.
It's probably only there for pedestrian safety, could even be detrimental to occupant safety. The only reason I can think of for having a weak bar and not putting sensors on it, is preventing airbags from deploying every deer or mailbox hit.

Unfortunately no one's been crazy enough to spend a hundred thousand dollars or so testing this, but I'm a firm believer of putting as much steel around my safety devices as I possibly can.
Can't prove something you haven't tested, especially with an insane amount of variables.

The purpose of these modifications is pretty specific, and you just have to determine for yourself on the protection sliding scale (yours/your vehicle VS others).
That being said, the only reason I don't have arb on my short list is how far it sticks out (again, probably because of the crush system).

If I drove more in the city, or had my pedestrian hit count anywhere less than one-infinitieth of my deer hit count, I'd be singing a different tune on my previously mentioned sliding scale.

 

Thanks for posting that. I'm only a couple of sentences in. I'll come back in a bit after I read it all.

But just from first glance, I see what your saying. The deployment thresholds are altered.

My argument has always been (even if not eloquently stated) that the worst case isn't altered and may even be improved by a steel bumper. The best cases or intermediate cases aren't as bad as the worst case.

In other words: I'd gladly accept a 2% (or more) chance to break my nose for a 0.003% smaller chance of death.

Now to read the white paper..

 

ARB Ι believe is only repeating the tests Toyota (or Ford or whoever) had to do to pass Aussie regulations and under those set of criteria the crash response doesn't change.

BTW, I also would mention that I do not know for 100% fact that ARB performs the same analysis or crash tests on Tacoma bumpers. They might but I don't think the U.S. regulations are as strict so that may have an element of Internet wisdom. I think if nothing else ARB has the resources to model and predict in software how their bumpers work which is something smaller companies can't do either. Much less do actual vehicle crash tests.

I don't think the crash bar is supposed to stand up to anything as such. It may direct where the energy goes, maybe driving the engine down, preventing the bumper from collapsing at a known rate. I dunno. But it wouldn't be there if it didn't serve some purpose that Toyota needed. We have to accept that in crashes vehicles are expected to disintegrate themselves to reduce force that ends up inside and bumpers expected to stand up to bouncing off rocks and winching are designed to do the opposite.

Frankly I don't disagree about the appearance, especially on 2011+ and 3rd gen it's starting to stick way out. But pedestrian safety with empty space factors in. This is a huge thing in Australia, how are you supposed to make a bumper that can stop damage from a kangaroo at 80 km/hr but not break the skin of a granny stepping too soon in a crosswalk at 10 km/hr? Seems like two wildly different criteria to meet.

 

Paper was a lot shorter than it looked lol.
Also kinda further proves my point.
In all the equations the weight and stiffness are divided against each other. No fancy squares or logarithms involved. Simply W/K.
All of the other stuff is based off of that with some maths, like time of impact. You usually want the time increased.

Anyway, since it's a simple multiplication problem: you want your weight as high as possible, and your stiffness as low as possible.

Adding a steel bumper adds a lot of weight. Give or take 4% of total vehicle weight (more more if you only consider the front weight). I would be surprised if making the front connection point (couple inches) stiffer has much effect as the other 8ft of frame and crumple zone and engine combined. Maybe it makes everything 4% stiffer. In which case, it's a complete wash.

None of us really know enough to be speculating about any of this, but here's another educated guess:
Doesnt really matter for passenger safety what anything but the passenger compartment VS the passenger movement is. Don't care what my hitch, or battery does in a crash. I care about my face and steering wheel distance/acceleration is. That's where the sensors that should control the exact timing of the airbags (simplification), all other other sensors on the frame/bumpers/whatever should just control whether or not the airbags will go off, not determining how close your face is. (since you are directly connected to your seat, not your taillight).

I'll take the tradeoff of having airbags go off in 1mph slower situations than they would otherwise, as long as I can ram rocks all day long in moab without replacing $2,000 bumpers every Thursday.

 

Implicit in their equations is the impulse characteristic and response. The "crush" or "stiffness" are described by non-linear dynamic models that the paper just leaves referred to the Vehicle Crash Mechanics textbook, which is 500 pages of joyous transfer function derivation!

 

Explicit in their equation is mass, and stiffness. Taking a ridiculously complicated multi-spring/dampener/mass system and boiling it down to a stiffness value is something that just has to be tested and simplified. Like they did. With real data.
I want to shoot myself if I ever have to solve vibrational analysis like I used to for class, years ago. I have now forgotten more than I ever learned about it. Except this one key takeaway point: fck that noise.

Again, I'd rather be in the semi than the miata.

 

Indeed. Problem I find is my luck leads me to find the inevitable bigger, faster semi.

Filter response is my background (analog electronics engineer) so it's interesting finding mechanical parallels.

 

Triggered. Mixed signal IC design engineer back when the drugs were pure. Went into driverless vehicles after.

Obviously not my field but there are some very smart people involved in mitigating pedestrian and occupant injuries. I think the cognizant engineers would tell us not to mess with safety-related systems. I guess you have to take into account peoples' exposure to the hazard, if you never drive in Homeless Despot parking lots have at 'er. There are kids in my neighbourhood and I want them to have the best chance.

 

Should probably sell your truck and get a smart car, then glue pillows to the front...

In all seriousness, one of the major reasons I was adament that my truck came with BSM and my refusal to delete that system by adding an aftermarket rear bumper. For some reason all parking lots are safe for me except for safeways, people just keep trying to get run over at only those stores....

But I've also done serious damage to vehicles with deer at 3am, and that's after kids bedtimes, so gimme all the front armor possible. And let me keep my beepers when I get a rear bumper..