Flygtenstein

Sparked from the other thread, and I think in the right forum since we are talking about how to build things to protect the rig...

Why would one want a dentable, deformable and destroyable bumper?

People occassionally dent .120 wall sliders which is effectively 1/8" but has the tublar strength gain going for it. I have never dented my 3/16's bumpers, but they all have pretty severe rock rash.

My skidplates are braced 1/8 and get hammered straight every couple of trips, but that is because the whole thing is a plate and meant to deform. Why would that help in a bumper.

Shane

Yes, you're safe this time Adrian.


"Dentable" makes me think of "crumple zones" whose sole purpose is to absorb energy in order to protect the cabin of the vehicle from shock and intrusion. However on a low-speed offroad application I don't see a point in designing something to purposely deflect/deform. Speaking bumpers specifically, I sure as hell don't want it to fail when yanking on it with a strap, winching off it, or using a hi-lift.


Hmm, on-road safety perhaps? There has been a lot of controversy about bumpers like we build and how they can "slice" into another car. Here in Washington a local group was apparently lectured by a cop while airing down about a couple of bumpers that didn't have enough flat surface area or something like that, they were tube bumpers.

ravencr

Adrian, I'm with you completely. All my stuff is 3/16" thick and no dents yet either.

Chris

rockota

"dentable" or "crushable" bumpers absorb impact energy, thereby slowing deceleration, so the person's body has to absorb less shock.

Also, again in theory, a slower speed "crash" will transfer less impact to the frame because the energy is absorbed by the bumper. I guess that could mean less chance of frame damage, and thereby lower repair costs...

The irony about this, is that it flies in the face of everything that we learn from motorsports...

.120, .188 and .250 for me, please.

Flygtenstein

Thanks Shane. In the business, I am what they call a trainable idiot.

For onroad collisions, give is good. In fact, some alaphabet soup place makes it so you have to. I am talking all and only about rock crawling bumpers.

To me, the rate at which 1/8th crumples will likely do little in lessening the shock my body or truck is experiencing. Most people do it this way and have no issues. Heck, the Marmot has 1/2" thick aluminum on his front bumper. He has had bending issues, but at thickness I would come to expect it.

Nitro Hotpants

The way I see it (like others who have responded here), is that for slow speed crawling you would want something that would maintain it's integrity instead of bending. This is of course when in regards to going slow where being able to "skid" past something would be far more beneficial than denting and possibly affecting other parts of the body as a result of the dent.

Of course from the on-road standpoint it is inherently better to have something that will "give" allowing for the bumper itself to absorb the impact.

Then again I believe weight factors in as well. While 1/8" is thicker and thus stronger, it does weigh more. I suppose one would have to weigh their options: lighter and "dent-able" or heavier and stronger.

Whatever floats your boat I suppose

Albuquerque Jim

You mean 3/16", right Casey?

My preference is to have something that will not crush when I need it most.

When finished, my bumper "slider" will be made from 1/4" 2"x2" square and .120" wall 1.75" round tubing

Nitro Hotpants

yes, you are correct, my bad.

jimbo74

you must look at it this way, yeah your offorad bumper made out of your thick stuff might be great, but if yuo hit something hard enough its going to hurt you more than the skinny bumper that was made to deflect a hit.... also the bigger heavier bumper allows more torque to be applied per hit than a regular bumper and this will make the chance of bending the frame a high probability... the frames are strong and decently thick, however have you actually seen how thick they really are? if you are running a bumper thicker than the frame itself, the thinner metal is going to damage on impact before the thicker....

Flygtenstein

Thanks guys.

Those of us with 4wd who crawl on rocks need 3/16". I think that is a bare minumum. Going to 1/4 is overkill on weight and thickness. The strength and rigidity pick up at 3/16's is apparent and worth it.

I have whaled on both my bumpers. Nothing is bent. This includes some drops of 2-3 foot ledges without issue. Having something that would deform would likely catch and hold me up. I like having beef to drag.

Albuquerque Jim

I respectfully disagree. For my rear slider application since it's only 2"x2", I think 1/4" is right on. The factory trailer hitch and brackets are 1/4" so that's what I based my design on. Plus I found a piece of 1/4" for $20 . With rear wheels hanging in the air going off a ledge I like knowing that I have 1/4" between me and the rocks.

I have seen this and watched the onlookers cringe

westy44runner

3/16 is bare minimum in my opinion also. However, going thicker doesnt always mean it will weigh more...it all depends on the bumper design...I've got a rear bumper that is built 80% from 3/8 but its very low profile...I've backed over ledges, pulled and dragged boulders over...1/4 would probably be just as effective..but I guess you never know.
As for crushable type bumpers for off roading...I think that would be a limiting factor too, I could just see someone drag over a ledge or drop onto a rock and the bumper just conform around the rock..ouch
Here's my rear


Brian

rockota

Oops - my bad.

I actually agree with you... 3/16th is minimum, depending on design.

ravencr

I have 1.5" square tubed sliders that are 1/4" thick, and my rear bumper is all 3/16" thick. I've slid, dropped, scraped, landed on, etc each of them, and I have major scars but no deformation. My sliders have been landed on extremely hard many times over, and in my opinion 3/16" -1/4" is bare minimum for sliders.

My new gas tank skid plate will also be made all out of 3/16" plate too.

Chris

Flygtenstein

Going thicker doesn't mean being heavier?

What?

The same bumper will weigh more built out of 1/4 than out of 3/16.

Jim, you are special. In that instance, it works. When it is reworked, it will be a heavy rock smashing SOB.

Albuquerque Jim

I like to be special

westy44runner

no you are correct, going thicker will weigh more obviously if you compare the same bumpers...but on my rear bumper its very low profile so i was able to get away with going with a thicker material instead of a larger profile bumper with smaller material to try to cut down on weight at least somewhat...

crash

I don't have a bumper on the rear of my rig, uh oh

My old bumper was made from 1/4" 2x4 and I was able to dent it, but there is a long story to that one

IMO building a bumper to deform/dent is just dumb, then again building a bumper that unbolts is also silly in my book..

BruceTS

The design of the bumper is the key to what thickness material your gonna need and what purpose it is intended for. The 3rd gen 4Runner frame is quite thin, so considerations should be taken on not building something too strong.

At first, I thought my factory trailer hitch was 1/4" but after stripping the powder coating and measuring, it was actually 3/16". Personally 3/16" is more than thick enough for most situations, like mentioned in rockcrawling your going slow, so the odds of denting it is near impossible. Another consideration is weight, the more you add the lower your gas mileage is gonna be, provided it's you daily driver.

Look at ARB's front bumper, they designed it to crush druing a crash, then there's TJM's that many users have posted how they didn't even get dented during minor fender benders, both made out of 11 guage (1/8"). I would have made my entire bumper out of 11 guage, if it wasn't for the fact that I also use it to tow my boat as well.

I've pounded my rear bumper hard against rocks, dropped off ledges, had it yanked on hard enough to lift my front wheels off the ground and all I've ever gotten was a two minor dents that took 5 minutes each to pound out. Since the body can flex upwards of 2" from the frame, a large gap between the bumper and body are needed, but if the bumper could flex as well, the gap can be made smaller, provided some sort of bumpstops could be incorporated to prevent contact. I use rubber weatherstripping to hide the gap and act as a bumpstop, which has prevented any body damage.

Is my bumper "dentable" yes, but it's still far stronger than stock, can 3/16" bumpers get dented? yes, but you risk damging your frame as well if it should occur.

Bumpers, rocksliders, skidplates all serve one purpose, to prevent damage to your rig and should be considered an expendable resource.

914runner

My rear bumper that is in progress (for the past few months) is being made entirely out of 3/16" or 1/4". But I am also planning on bracing the frame a bit.

The reason I am going so thick, is because my bumper will do dubble duty as a trailer hitch. Otherwise I would probably go with 1/8" for the weight savings. The 3/16" is for towing strength, I wont be bashing my bumper on rocks very much.

Since it will be so heavy I will probably end up having to put the cruiser coils on after all. I wasnt planning on putting them on but since my Downey HD's have sagged a bit with my heavy cargo box in the back all the time the heavy bumper is only going to make it worse.