Engineers would this tow hook bracket scare you? | Ford Explorer Forums - Serious Explorations

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Engineers would this tow hook bracket scare you?

Hokie

Hokius Maximus
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City, State
Denver, CO
Year, Model & Trim Level
'98 TJ Sport
Here is an idea that JasonB and I came up with to address tow hooks on my '99 Sport. Basically, its a 4"x3" bracket made from 1/2" plate that drops the tow hook to a useable region (visible through the bumper)

According to simple calculations, a 5000 lb pull on this hook will yield a 800-1300 ft/lb torque on the frame (acting inbetween the upper most bolts). This originally scared me, but then I started thinking about trailer hitches.

It is readily accepted that towing/pulling from a trailer hitch is fine.

Assuming a hitch with a 10" bracket from the frame, a 5000 lb pull will yield a torque of ~2000 ft-lbs per frame rail.

So my question is, engineers, would brackets like this scare you to mount tow hooks too? A front trailer hitch would drop down even further from the frame rail and will enact a greater torque on the frame. Also, these would be made with 1/2" plate steel, which is really DAGGUM strong! I'm thinking this may be my best option for front tow hooks. (I don't want a front hitch)

Thanks bigtigexplorer for the pic that i cannibalized.
 

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Mine would look the same from the front... ('cept the hook would be flat)
 

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You'd think it would work wouldn't ya!
 






Originally posted by WannaBTrckmagik
You'd think it would work wouldn't ya!

yeah, and now i'm thinking about my buddie's winch ready bumper on his XJ. If the winch is mounted on top, there will be a torque enacted, and the tow hooks on the bottom will enact a torque. That, and on my X, the frame up front is alot thicker than in the back (and is completely boxed). I'm pretty sure i would be fine doing this.
 






I think as long as the bolts could handle it without shearing, you should be fine. That is really thick steel and our frames are pretty crazy strong. If it really freaked you out, you could add a strip of horizontal steel between to bolts that spreads the force out further on the frame to strengthen the system, but I doubt you will need it... unless you are going to be pulling with 10,000 lbs of force, like jerking the dead weight of your truck for some reason.
 






Yeah, my curb weight is 4100 lbs, so there's no way i'll tow that unless i'm COMPLETELY stuck in the mud. I'm not trying to pick up the truck, just pull it
 






Do you understand what I mean about extending the distance between the bolts? The further out you spread them, the less likely your frame is going to be to buckle. You could also add a 3rd bolt a little higer up (3"x5"?) and add a matching plate on the back that connects the bolts on the back. That is about the most even distribution you could achieve, without wrapping around the frame.
 






I guess I could get some 4" wide 1/4" plate and have one come straight down and the other wrap around the other side of the frame and bend in next to the other bracket. That would take some of the load off of the drilled holes (looking up stress concentration charts in my deforms book) and transfer it to the frame. Hmm.. that may be what i'm going to do
 

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The only problem I see with droping the hook down like above. is if pulling from the side. that might bend the steel. but with a straight pull. the steel would be strong being it will be pulled > straight.

as nweibley said as long as the bolts don't shear it should be fine.

to add strenght you could even weld a bracket to triangulate the bracket.

Tim
 






Hmm.. so wrap around brackets, with 2 triangular braces, these tow hook brackets would be pretty daggum strong IMO
 

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Yes... triangles are basically the strongest structure you can use.... that is a good design. However, I would cross triangulate from the back to the front, and the front to the back. That way, when you pull on the hook, the rear and front torques meet in the middle of the triangle X and distribute themselves evenly in the frame. I'm pretty sure you would need the help of a fabrication shop to pull something like that off.
 






Now you've lost me nate... Yeah, I understand the stresses involved, i've taken deformable bodies, statics, and I'm taking Mechanical Design right now. For the sake of feasibility (no welder) here's how i would probably make it (everything being 1/4" thick)
 

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Haha, I haven't taken any of that crap, I just know a few things and am thinking practically. I think between you and I, that is the best design you are going to get without a welder. Looks pretty darn safe to me, just tie a tee shirt to each end of your tow rope so if one of your hooks comes loose, it wont fly through the air with the greatest of ease and kill anyone!

Lookin good though! :D
 






If I pull hard enough to break a hook, you think the weight of a t shirt is going to do something? ;)

I can see it now, when you finish your BL, you're going to be buggin' me to fab you some brackets just like this :p
 






i dunno it seems like it would work..i have the same 99 sport as you except mine has a brushguard on the front..i was thinking about bolting my hooks into the metal that goes from the guard to the frame..it seems like pretty sturdy sheet metal..just a little afraid it might pull the guard off in the process of being towed or pulled
 






Brett, I think you're thinking about this too much. From an engineering and an operations/managerial stand point, simplofy the hell out this thing and just stick with the original design. You need to consider how many times you are going to get stuck (prob very few) when a simple tug won't pull you out. And even in those cases, you can wrap the tow strap around the frame under the bumper and it pulls just fine with no damage.

All this torque stuff is over the line. The Ex frame is too strong for its body and too heavy for its motor, thats why Ex's start to lag in old age. You are more likely to sheer a leaf spring bolt than you are to sheer a makeshift tow hook bolt... just my .02
 






I agree with VABA, and I am an engineer. I am going to have plates made at the a machine shop as soon as I get a little caught up at work. Do the math, use a 40 ksi steel, an 1/2 inch bolts. It should pull about 15 kips. If you are that stuck you are going to need a backhoe to dig you out.
 






Also an engineer. Didn't do the math but it should be way fine, go with the simple design.
 



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Well, talked to my Mechanical Design Prof. and my gf's dad (NASA engineer) today. They both said that i would be safe mounting the hook to the steel or the frame using grade 8 bolts. Unfortunately, its hard to tell what would be the 'fuse' in the system. Chances are the frame would tweak before one of the bolts would let loose/shear. Hopefully, my strap will break long before I ever get to that.

Anyway, I'll either make the 1/2" bracket and some side strips for stability on off center pulls, or just say frag it and mount it directly to the frame at an angle like bigtigex did. Brian made a good point, I don't plan on using these very often, and when I do i'll have to reach through the bumper, so i'll feel safer having it frame mounted.
 






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