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Too much bumper = frame cracks :(

blistovmhz

NAXJA Forum User
Location
Vancouver, BC
I built a rear swing out tire carrier bumper for my XJ. It's mostly just 2x6 1/4" tube.
It's modeled after the Roxolid carrier bumper, but I wasn't happy with bolting it to the stock (paper thin) bumper mounts, so I instead mounted it inside the rear frame rail as far as I could get it (around 24 inches).

Then I bolted it all from the bottom and called it a day.

Well, turns out this isn't a great idea for several reasons.

1. The 35" spare is heavy and it wants to move. It can't, but every time it tries, it's stressing the uni-frame rail.
2. Flexing the Uni-frame rail and NOT the bumper = stress cracks. They're about 2" long on the bottom of the frame on both sides. Uni-frame twists, bumper doesn't.
3. I wheel it hard.

I figure there are three answers.
First, just remove the bumper and start fresh.
Second, plate the entire uni-frame and cage the uni-body. This would work, and I'll probably do this eventually, but I really don't feel like tackling this over the winter and I need a solution soon before I destroy what's left of the frame.
Third, (I just thought of this today) plate the section of frame rail where the bumper bolts in. Sides and bottom, another 1/8" of plate, then drill a single hole through the side of the rail and bumper, stick a bushing through, and bolt it in using only one enormous bolt. This would allow the frame to flex and there's enough space in the rail for the bumper to move around a little bit.

There's also the issue of the carrier trying to bounce back and forth. If someone's got a good idea on how to stiffen that up, please let me know. Otherwise I'll end up tying it in to the roof rack when I cage it.

Here's some pictures for reference:
IMG_20141020_162818.jpg

IMG_20141020_162834.jpg

IMG_20141020_162735.jpg

IMG_20141020_162747.jpg



One last thing. I absolutely hate having a spare tire on the back. I've landed on that spare tire more times than I care to admit, and when it hits, it hits hard. I know I should avoid doing this, but sometimes it's just inevitable. Aside from the swing out carrier or roof rack, wtf can I do with a 35" spare? Yes, it'll fit in the back, but that means the rear seat has to be folded down to make room for tools and trail spares. I hate having the entire back of my Jeep full of tools. I can't have a grocery getter that doesn't have room for groceries!
 
Realistically you only have 4 options for your spare... Tire carrier, roof, in the back, or leave it at home...

Yea, and carrier sucks, roof makes shit too tippy, in the back sucks, and I probably SHOULD've left it at home, but now my wheeling I think sorta requires a proper spare. We're getting too far away from home, in sharp rocks. ;)
 
Air down the spare to about 1-2 psi or less, put two ratchet straps across it to make the opposite sides flat, and it will fit lying flat in the back with the seat up. Obviously have a compressor to air up a bit before you use the spare...
 
Leave it at home or trail head/ camp ground.

haven't had a spare tire with my last three vehicles.
 
My solution would be to raise the tire up higher (that would reduce your view through the rear window) and reduce the amount of air in it. An air compressor would be needed when you need to use it.
 
Cage + plate.
Tire inside.
Shelf or drawer to get back some cargo space.
 
Fix your subframe, add metal to the underside of the rails with a cross brace between them for some support, change your driving habits so you don't land on your spare anymore and just enjoy the damn thing... :p
 
Just an observation.
Most of the OEM tire carriers I have seen (Ford's, Nissans, etc..) all had some support from the rear hatch. On a Ford Bronco I owned there was a support stub on the rear hatch with a thick rubber pad that a tab on the carrier just slid up on taking "SOME" of the load.
Maybe spreading the tire weight out a bit like this might help?
 
Your mount is nothing like theirs I have one and know that it is one of the heaviest duty ones made and in fact could never bend your frame period. I have even pulled a trailer with my built-in receiver hitch before weighing well over a 1 1/2 tons.

Here is a photo of mine, sorry don't have one of the mounting to hitch nut strips but I'm sure everyone knows what I'm talking about.



Where you screwed up was not using all of the bolt holes in the Class III hitch mounting, those nut strips are where all the strength comes from not just the bumper mounts. Mine has been on for over 2 yrs. and the price was so cheap at $600, powder coated and all hardware, delivered it would not have been worth it to try and make one.
 
Is your bumper not tied into your nut strip?

He did say it was tied in with the nut strip. However looking at the picture he posted, it seem to be too low for rock crawling or as he said coming down off rocks. That tire will get hanged up on rocks in a big way and probably suspending the back of the XJ in the air.

Compare the picture he posted with the picture posted in this link,...http://naxja.org/forum/showthread.php?t=1030354&highlight=swing+tire+carrier . Pay attention to the top of the tire against the roof line. You get the picture.....
 
The bumper is tied in WAY further than the stock strip nuts :). All the way back to where the frame rail starts bending down and in. Tonnes of support, but probably should've tied a few bolts through the side as well so all the weight wasn't on the very end of the rail.

The problem with lifting the tire up higher is that if it's going to be any higher, why not just stick it on the roof? Also, moving the tire up higher puts more leverage on the bumper/frame.
Why can't we just have a full size spare that doesn't take up any room?


Okay, so I think it still comes down to my original three options, and the first two have issues.
Moving the spare to the roof sucks cause of COG, and putting the spare in the Jeep takes up a tonne of room that I really don't have and doesn't look nearly as badass as a carrier. Yea, I know, I generally don't do anything for the sake of looks, but I really dig tire carriers. Only girl Jeeps don't have a carrier.

That leaves me at plating and caging though I think. So, how crazy does the plating need to be? Ruffstuff's stiffeners are only 3/16 and only cover one side of the rail, and don't go all the way to front/back. I can fab up some more plating for the ends, but should I be boxing it all in, or just the ends where the steering box and bumpers bolt in?
 
Hd offroad has front to rear stiffeners, but the rear are just the side. Wouldn't be too hard to plate the bottom and even the inside.

I would look at angling your tire to match the hatch, will help with coming off ledges. That is how my rigidco is.

I also added the inside-the-frame rail mounts and incorporated those into the hitch mounts and the submounts on the rigid. I've considered welding them in place since the bumper is actually removable from the subframe. Maybe consider something similar with yours? Also maybe pull it in another inch or two, looks like the bumper bar itself is hanging way out there.
 
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This is a 37. On a steel wheel. Never a problem. Mine follows the line of the hatch.
 
The factory tow package is built for a 500 lb trailer tongue weight.
I've got to think it's the hard landings on the tire while you come down off stuff that is doing it.
Move it higher, stop doing that, or move the tire inside.
Or, I guess, add 1/4" plate everywhere in sight & tie in to more stuff & on and on until you stop breaking things.
 
I was thinking if the hits are making the frame crack...
1. drive more careful.
2. Build a removable spare tire skid plate that goes in the hitch mount and is angled for less force being transferred and acts as a slide.
 
Move it up and tilt it forward like I did on mine. No problems.

What about centre of gravity? I haven't really TESTED with spare on and off, but adding that weight that high up seems like it'd make things tippy . Anyone running 6.5" and 35's, actually know how big a difference having the tire up that high is?
 
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