Bumper, keep my BSM

Heya, it's about time to start planning out my bumper protection since there's not anything commercially available. (If I'm wrong please enlighten, thanks).

I'm thinking of getting either tube or square steel welded to the square tube of the hitch. Keep the stock tin foil bumper and just give it some protection (that way I keep BSM untouched).
Wrap the bottom and rear quarter panel and the back with steel. The hitch would still be the low point.

Ok, the reason for this post, 2 questions.
1) What's a good way to mock up? I was thinking either spend hours with cutting pvc and gluing, or thick wire and a pool foam tube thing. Ideas welcome.

2) Does anyone have a good idea of forces I should design for? I'll nab a copy of solid works or something and figure out what supports I need. (or tube thickness, etc). I was thinking just the trucks weight, but then I started thinking about impact forces, so my question is what I should design for in order to not have contact.

Thanks!

 

bUmP

 

Cardboard or sheet foam for mock up.
Nothing you build or buy will be safer for the passengers than stock OEM. However, you can build something that will protect the truck better when going offroad. Protecting the truck or protecting the passenger are two different things.

 

But not mutually exclusive (on a scale that matters).

In the end, want to protect passengers by protecting the truck. The first time I catch the bumper on a rock and rip it off, then drive home, I'll merge into a bus full of nuns because my BSM got ripped off.

For the front, I've hit more deer than people, but luckily there are already commercially available bumpers that don't sacrifice safety...

Forgot sheet foam existed, thanks!

Any idea what forces to use for FEA? I can only find the "hilift test" which is significantly less than an impact.

 

Lol there is absolutely zero chance that you can simulate a crash using FEA. You might as well just use a simple force mass equation for as close as it will get you. Auto producers have a lot of computing power yet they still crash test, even if government or insurance does not require it. Too many variables. Good luck and don't mod any crumple zones.

 

Is it "not" possible to retro-fit the BSM sensors into an aftermarket bumper? Just need to drill the right size holes in the right location?

 

You won’t be able to really do anything unless you completely relocate the BSM and there is really no good place to put it.

 

I am going to use a simple force equation. My question is what force to use. I will use FEA to see if any points (specifically the weld area on hitch frame) will fail and if I need to add bracing somewhere near the rear tire. I also need to see what kind of deflection I get to see if impact with stock bodywork is likely...

I also haven't seen any crash tests for rock crawling, like ever. But I have seen plenty of people selling bumpers and sliders showing the "hilift test". I just don't think using 1/4 to 1/2 of the truck empty weight is enough, but where to stop?

Not really. The problem is aftermarket bumpers are "too good". Take my thought process for a grain of salt but all the aftermarket stuff is too strong and bumps get passed right to the sensor making it fall out of alignment. The current stock bumper absorbs those small bumps and deflects instead of transferring that force to the sensors. Which is why I want to make a cage around the stock bumper, and not fck with anything the sensor attaches to.

Agreed. I really wish Toyota put it in the brake light like competitors. Instead we gotta design some gigantic hopefully not ugly contraptions around it.

 

I can tell you where to stop on the velocity component... 45 mph. Nothing survives beyond that velocity.

 

We'll, that's definitely on the other end of the hilift test. I was thinking more about scraping against a tree or falling 6 inches onto a rock... Things that sliders and other Offroad accessories are there to protect against. Not battling semi trucks on the freeways lol.

 

Only thing I would add - Caging your OE bumper to the frame will change the way the crumple zone works. But, you have to Rock Proff somehow?

 

You need to protect your passengers first.and foremost. We spent a lot of time and research awhile back weighing the safety of a cab mount chop. What we found is, if you crash above 45 mph head on against same or greater mass, nothing will help you and you will be dead.

 

The OE bumper is already attached to the frame right? And I've done the math in one of my past posts that the bumper crumple zone accounts for like 0.001% of the forces. That's like having your finger pricked of blood loss when your already going to have 74 broken bones. It's the parking lot and offroading where you go from thousands of dollars of damage to $3 of spray paint.
But what's Rock Proff?

Which is why I won't be getting larger tires. Thank you and this entire community for figuring that out. That shits scary. But there's just no way I can be convinced (or at least not with what I've seen yet) that adding extra stiffness to the bumpers does anything detrimental to occupant safety. It's not good for deer or other people cars, but I can't wrap my head around changing anything about the cars crumple zones for the simple fact that the bumpers already exist outside the crumple zones.

Which again, I haven't seen anyone (OK well aside from one awesome video) try to design an offroad bumper that's supposed to survive a 68 foot (45 mph from free fall) drop onto a rock. I'm asking what force (or drop) I SHOULD design for from people with a lot more experience offroading than me. (some things I shouldn't have done in high school in Alaska)

Edit: the whole reason I want this is I know I will make mistakes, and I don't want them to cost a fortune.

Edit2: and I refuse to drive around in a new truck that looks shitty with bumpers half ripped off etc. So, add steel or be a mall princess like everyone here loves.... I just wanna get out there.

 

Your stock bumper is the beginning of the crumple zone, which means that is where the initial decel of forces start. If you remove that, your passengers will see more g's upon impact. That's easy.
The only bumper I have seen crash tested is the ARB. Adding pipe or tube is just going to remove your first line of crumple at low speeds. Can you or your passengers handle more g's in the event.of an accident? Your.call. My thoughts are no. Especially if hauling around my granddaughter other small child. As you know crumple = decel = lower g's = survival. It's easy to build something to keep your truck from damage. It's hard to protect the passengers inside.
Truthfully, the best scenario is a full cage, 5 point harness, HANS and a helmet. Then you could go crazy protecting.your bodywork. The realistic fact is that will never fly with normal day to day usage. So anything you do will be a compromise between passenger safety and truck protection.

 

Again you are technically correct but imperceptibly so and perhaps even outright false.
Luckily this is all multiplication so easy to follow.
1lb going 3mph has 0.40792 joules of energy. Say that's the crumple zone equivalent of a stock bumper.
1lb going 45mph has 91.781 joules.
Absorbing the first 0.4 joules is only .004 of the energy. Or 0.4%.
Adding say 150lbs of mass to your side of the momentum equation results in about 4% extra weight. (150/4000)
So if you add more weight to your vehicle, your passengers will suffer 4% less speed differential, lets Calc that out... (. 0375x45=1.69).
So now you will lose 43.3mph instead of 45mph.
Lets Calc that joule equivalent for 1lb...
And we get 84.978 joules. Hmm. That seems to be significantly less than 91.7. It's only 92.6%!!
So by losing 0.4% energy absorbtion, you have to absorb 7% less? Seems to be WELL in my favor....

Must be some benefit to being the guy in a semi truck if mini cooper's keep hitting you... Oh, like we see every day, for the past 90 years...

Now, yes, there are more variables, but, yet again, getting rid of the piddly ass crumple zone in a tin foil bumper is Negligible, like I've been saying.

Edit: my point being that you completely solve low speed impacts (parking, rock crawling) and don't really affect high speeds. Hopefully getting dinged by shopping carts doesn't cause whiplash for passengers after you get rid of the tinfoil bumper...

 

Just buy a tank and be done with it.

 

Some bumpers already have the cut-outs — C4 Fabrication does

Not sure of your concern about the sensors “falling out of alignment” from impact with an aftermarket bumper. It would have to be a direct strike on the sensor itself for it to make any difference how strong it’s surrounding material is.
That said, the factory bumper is likely weak enough that an impact six inches to a foot away would bend or shatter it enough that your sensors just hang by the harness, or face the wrong way. I mean you’ve seen how weak that factory bumper is haven’t you?

 

I thought C4 quit making the bumpers with the BSM cutouts? Had issues with the BSM actually working correctly post install.

I was/am in the market for a rear bumper that will retain the BSM feature and I haven't found it yet. Could modify one to do it, but I'm not a fabricator.

 

Look at decel over time. That will equate into g's on a human. Again though, this is all low speed stuff. What will set off your airbag? Rate of speed change right?

 

I actually purchased the TJM, but promptly canceled the order after learning about the 2018-2019 BSM radar located in the bumper. Although, I'm actually reconsidering ordering the TJM... I'd like to cut a hole in it for the BSM radar and cover it with a curved piece of plastic similar to the OEM bumper. This might take care of the BSM issues that C4 Fab had (here).