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Discussion Starter · #1 ·
I'm sure someone has built one of these before, but I can't seem to find anything. Following the style of the front stubby I built, and using the remainder of the materials I have, I'm thinking I'm going to put something like this together.




The base bumper will be the 2.5x9 Cchannel with the ends boxed in. On the lower portion of the bumper, ill have a mount on each side with a piece of 1 inch stock welded into it. The one inch stock will be what the carrier pivots on. Above that on each side will be two C shaped brackets with holes drilled through them for locking pins. Between the tubing and the bracket will be a rubber pad.

The ends on the carrier hinging on the 1 inch stock will be a piece of welded tube filled with delrin bushings ill turn out.

When the bumper is in upright position, the weight will be supported by the two pieces of stock and the retainer pins. When in a lowered position, the mounts for the 1 inch stock will be extended enough to stop the carrier from folding to the ground.

The idea stems from a trailer gate I made which weighs 140lbs and rides on similar style 5x8s pins.

I don't think there will be any danger of breaking anything, but I assume 1.25 inner diameter schedule 40 pipe will be sufficient? The largest amount of force will be applied to the whole assembly when the tire/carrier is resting in its folded down position.

I realize the idea might seem inconvenient, but I only open the rear when we travel or go camping, otherwise I simply toss everything in the rest seat area. The tire and metal will weigh less than 100lbs....which is nothing when you add in its on a pivot.

Thoughts?

I'm not using a spindle for the simple reason I'm doing this bumper for minimum cost. I already have all of the material, unless you thick I should use square stock for strength as opposed to pipe.

Still working on an idea for a proper bolt on mount for the rear.
 

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Looks like a nice idea.

I do stuff like this at work and I can check some things out tomorrow hopefully when I get a chance. But since my bumper is encased in ice and snow, can you find some things out about the bumper mounting?

1. Mounting bolt size and quantity per side (I think the front bumper is two M8's per side, a couple inches apart, in shear load?)
2. Farthest distance between mounting bolts on either side.
3. Approximate distance from set of mounting bolts out to to center of tire when folded down.

I'm also thinking you might want to move the lower crossbrace up above the locking pins and make the hinges and pin clips one continuous section that covers more of the C9. That will give more surface area supporting the gate when down.

I'm sure the pipe would be fine. I'm just concerned that if anyone decides to sit or lean on it or rest a heavy load on it, or even pull the pins and let it drop to its stops, the cantilever load might snap the bumper bolts or bend something. Looks like about the equivalent of a frame hitch with a 200 lb tongue weight but hanging off the bumper not the frame. Rubber pads on the downstops would help ease an impact if it dropped and would be nice anyway. But if I knew more about the bumper bolt area (questions), I could figure it out better.

Or if you have a different way to bolt it up, let me know when you get it worked out.
 

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Discussion Starter · #3 ·
Looks like a nice idea.

I do stuff like this at work and I can check some things out tomorrow hopefully when I get a chance. But since my bumper is encased in ice and snow, can you find some things out about the bumper mounting?

1. Mounting bolt size and quantity per side (I think the front bumper is two M8's per side, a couple inches apart, in shear load?)
2. Farthest distance between mounting bolts on either side.
3. Approximate distance from set of mounting bolts out to to center of tire when folded down.


Or if you have a different way to bolt it up, let me know when you get it worked out.
Thanks.

Three m8 bolts in sheer up top 17 inches apart.

Two 3x4 bolts on bottom mounted in sheer.

Six inch bead on each end of bumper holding it to the reinforcement plates I welded to frame.

18 inches to center of tire when folded down.

Pirate4x4 guys were helpful.for a change and offered an interesting way to do the bumper. Which sparked ideas.

A single piece of schedule 40 1.25 ID pipe bent 180 degrees. A single cross brace between the pivot points and pin points. A 6.5 inch round 1/2inch thick circle welded to the top centered. A schedule 40 pipe above and below extending outward 9 inches to a 8 inch circle 5/8s thick, studded.

A single pipe will travel from the lower center brace to the backside of the 8in round.

I will use a section of schedule 40 pipe filled with delrin bushings around a 3/4 grade 8 bolt in double sheer for the lower hinges.

Extending outward from the bottom of the lower hinges will be a 1/4in plate for the bumper to rest on.

I will also cut two sections of synthetic winch line for a fail safe. They will stop the carrier from smacking the ground when lowered in the plate fails. And they will keep the carrier attached to the car if there is somehow a catastrophic failure.

Building it tomorrow. Have the bumper done, but not the carrier. Going overkill on the material for safety. It will not fail.

Ill post pics tomorrow.
 

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I've noticed hitch-mounted spare tire carriers on the Internet. If you place a 2-inch receiver on your bumper, such a tire carrier can be mounted.
 

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Discussion Starter · #5 ·
I've noticed hitch-mounted spare tire carriers on the Internet. If you place a 2-inch receiver on your bumper, such a tire carrier can be mounted.
That was actually the original plan. I even bought an extended hitch to build off of. The only problem is they rattle. A lot. To the point where you can't hear yourself wish you wouldn't have done it.
 

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I don't have everything with me but I did some estimates at home. Single piece of 1 1/4 pipe should be just fine. I was looking for side view but I found one side of mine and they are about 5" apart per side. (Better than the front bumper.) If they are 4" back from bumper then another 18" is 22". 22/5 is a 4.4 lever factor on those M8 bolts. 100# x 4.4 is 440# and a quick (probably low) estimate is 2500# to shear a M8. Looks like just static weight you will be just fine.

If it gets dropped it's another story. We normally farm out our dynamic calcs but I with what we have to work with, I estimate that unless you can cushion the stopper so it has at least 3" of cushioned travel (at the tire) to stop, if it doesn't blow through the stopper plate then it might shear an M8. Remember the forces at the stopper get multiplied by how much farther the tire is from the pivot than the stopper.

So your winch line is definitely a good thing. You can make the stopper to hold the static weight but break if it gets dropped then let your winch line take over. Or make the stopper real beefy but make sure there is a lot of cushion in it so if it drops it doesn't shear an M8. Your 3/4" bolts and reinforcements to the bottom will definitely help, how much depending on how beefy it all is.

Good luck with project and I too would like to see pics!
 

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Discussion Starter · #7 ·
You're working with a two door instead of a four I'm betting.

On a four door there is a 36ish wide bash plate welded to the rear frame that's reinforced enough to where I would consider it a fixed position. The whole frame would give before it would.

The top of said bash plate has three m8 bolts mounted across it. One inch behind the face. The bumper will be positioned using those three bolts. Ill bolt the bottom into the frame using the larger bolts. That along will be more than strong enough for the app. The six inch weld on each side to the pieces I added are merely insurance.

I was remembering my trig last night and used it to calc the angles and lengths out. When I got to the shop, I liked the angles but not the length. Came off the custom hub plate with two pipes on top of each other at a 30 degree angle, wnf then there is a 50 degree bend in the pipes.

Pics tomorrow probably. I'm going to join these two pipes to a 6.5 inch round.

Still trying to work out the beefiest way of securing a plate to the side of pipe.

Have some ideas with plating.

You gave me an idea though, if I get the winch line length correct, it has some, very minor, elasticity. If you I do it right, the line can take the brunt of the force if I drop it down.



I can't believe an m8 bolt has a sheer point of 2500 lbs. I thought it would be around 1k...if that. Charts say 400, but I knew they were wrong.

Pics tomorrow probably. Depends on progress in the chilly weather.
 

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Yes I was looking at my 2 door since that's all I got.

If I'm seeing this correctly, I would take some plate to connect from the rear face of the round plate, to the tangent of both sides of the pipe. Make sure the plates you add are vertical and are at least the length of where they meet the round plate, so you get the section strength you need to hold it in place.
 

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That was actually the original plan. I even bought an extended hitch to build off of. The only problem is they rattle. A lot. To the point where you can't hear yourself wish you wouldn't have done it.
I understand. I have an anti-rattle bicycle rack from 1UPUSA.com :: Home. There is a webpage touting various anti-rattle devices for a receiver hitch: Anti-Rattle Devices Review | etrailer.com. There is also satisfaction from your custom approach. Best of luck!
 

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Discussion Starter · #10 ·
I've been slightly busier with other stuff than I'd hoped.

Redesigned yet again, didn't like the weakness of the design I was going with. Decided to keep it simple while adding a few features.

Keep in mind, nothing is finished, everything rough cut.


I made some bushings from delrin. Very roughly done with cut off wheel. I'm going to heat them and pound them in to the DOM, then drill them out. Also made brackets for lower mount. First out of eighth, then quarter.. that's pretty much where they will be mounted.





Welded two staggered pipes to carrier hub. Then pipes will angle and br welded to a large piece of angle I had on hand.

Falling asleep...ask away...ill answer later.
 

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Discussion Starter · #11 ·
I've been slightly busier with other stuff than I'd hoped.

Redesigned yet again, didn't like the weakness of the design I was going with. Decided to keep it simple while adding a few features.

Keep in mind, nothing is finished, everything rough cut.


I made some bushings from delrin. Very roughly done with cut off wheel. I'm going to heat them and pound them in to the DOM, then drill them out. Also made brackets for lower mount. First out of eighth, then quarter.. that's pretty much where they will be mounted.





Falling asleep again.

More pics soon.





Welded two staggered pipes to carrier hub. Then pipes will angle and br welded to a large piece of angle I had on hand.

Falling asleep...ask away...ill answer later.
 

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Discussion Starter · #12 ·
Got a little more done, food poisoning shut me down for a few days. Brackets and stops welded up. No cleaning done yet so excuse the splatter everywhere. I'm considering adding lateral support to the stops...but when I stand on them and jump, no shift at all. So probably overkill realistically.

I my delrin bushings are TIGHT. Takes 50lbs to move them downward. Easier to move up. Handy.

Decided not to put any stops in for the tire. When it folds down it can just touch the ground.

Still going to add two synthetic winch line safety tieoffs to the assembly though. On the offchance of catastrophic failure...no one dies.





 

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Nice work in progress. Yes I'm sure your upper stops will be fine. As a general rule of thumb for straight tensile weld strength we use the size of the weld as a 4 place decimal, remove the decimal, use that number per inch. So 1/8" weld about 1250# per inch, and you don't have any side loads up at those stops.

Are you doing something about the free space around the pipe between the C9 and the pins, which may rattle? Like either crossdrill the pipe for the pin, or weld on a piece of cross tubing fit with a smaller delrin bushing for the pin? Or is it a closer fit than it looks?

Easier to move up, looks like that is from the geometry, how the pipes look to be tapered in a bit when raised, so making that the natural position, it takes more effort to bring it down and out of that position, and pushing it back up makes it easier. Hadn't thought of that approach.

Yes good idea to just let it drop to the ground in worst case. Then you don't have to deal with the stresses of a lower stop which will be immense. Worst that will happen if the pins come out, and the winch lines fail, is the spare will drag the ground till you stop.
 

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Discussion Starter · #14 ·
Thanks for the reply, I also didn't think of that. Just luck. I've since welded the dual pipes to the flat L steel. Deciding on how to brace the sides, or if I should. I feel like I should, but I see so many examples of tire carriers which simply have a hub suspended on a single piece of DOM. If they can do it with a single...and a 200lb tire. Seems as though a double tube welded on would support a 75ish lb assembly.

As for the pins.... going to take a trick out of the rzr community. Take a soft offroad tire and cut a few small squares. Drill a small 1/4in hole in the rubber piece and into the bumper. Fill with hot glue. Replace as needed.

It'll take 100+ lbs of force to compress the rubber, which will then exert that much force on the pins. It may still rattle, but only on very hard bumps. At which point, I doubt I'll hear it over the sound of my tool bag bouncing along the bare metal that is the bed.


Just bought the three stainless M8x1.25 bolts that will go in the top stock holes. Underneath, I'm tying into the plates I made as well with 6inches of weld per side. I've decided to also bolt on with the stock gas tank skid bolts.

I'm actually going to set the winch line to stop the tire 2 inches from the ground. It's rated for 8k lbs...so even if I managed to drop the tire/carrier the two lines should be able to handle the stress no problem.

Good to know on the weld four decimal rule.

As of right now, it's a little over 80lbs without the tire and wheel.

Sounds like a lot, but I'm oversprung with doetsch tech rears. I've put over 1k lbs in the bed...and only sagged maybe two inches. If anything, I'm adding a little extra weight here and there to improve the ride lol
 

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Discussion Starter · #15 · (Edited)
First test fit





About to grind, clean and prime.

My 5ft4 wife can lower and raise the tire no problem. Probably couldn't put the spare on the studs...but she never would anyways.

Its easy enough to raise and lower that I honestly wouldn't think twice about throwing stuff in the cargo area rather than on the rear seat.

Works better than I could have hoped.

And wont be bad looking...especially for a first try Fab job.

And if strength is a question...a buddy of mine says:


"Usually without and NDE (ultrasonic, x-ray, etc) a joint efficiency of .55 is used and the max allowable stress is calculated by using the throat area (.707 times the weld leg size) with a 70 tensile strength rod max stress theory usually allows ~30% of tensile.....
If welded correctly the plate will shear or the pipe will fail in tension before the weld breaks."

Short version....this thing isn't going.....anywhere.
 

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Nice work so far. If it was me I'd take a grinder and put a radius on the corners of the pivot and pin plates.

Looking at this last view, I can see a real advantage to this as it puts the spare (especially your 33) on a mount independent of the tailgate. Since the tailgate doesn't seem all that strong for supporting much more than a stock spare.

Like on mine I built a bike carrier that mounted to my 235-75-R15 spare tire and holds 2 bikes, but I definitely wouldn't go any more than that. I made it very light but strong, but something like you did would be ideal if I wanted to carry more. I'd have to remove the bikes to open the gate but I pretty much have to now anyway to be able to get the gate closed back up.
 

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Discussion Starter · #17 ·
I actually radiused all the corners except the uppermost point. Which might not make sense, but when the tire is laid to the ground..everything makes a handle ladder to reach onto the top. The uppermoust brackets make great steps.

I have had a roof rack for over a year and haven't put it on..
As soon as the bumper is done....that's the next project.

I need a place to put the kayak that doesn't bend the roof down.

 

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Discussion Starter · #18 ·
DONE







The "rope" is the synthetic winch line.

Should the upper somehow fail...safe
 
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