Rear Bumper/Spare Tire Mount Thoughts

[Gary Lewis]

With the 32" tires on Big Blue there's no way that the spare will fit in the stock place - and especially when I put the Bronco rear tank in.  Right now the spare is taking up much of the space in the bed, but when/if I get to go overlanding I'll want it out of there to free up the space for gear.

So I've been thinking about how to make a rear bumper that will carry the spare as well as serve as an air tank for the on-board air compressor.  But I was having a bit of trouble envisioning how to support the spare since it needs to pivot out of the way to open the tailgate.  However, yesterday we were behind a truck in traffic that had a Wilco Offroad Hitchmate Solo on the back.

As you can see below, that unit, which runs about $800, slips into the receiver and hinges on the right to swing out when the red pin is pulled.  I'm thinking of replacing the rear bumper with a piece of square tubing that is closed on the ends to serve as an air tank.  And the arm for the spare would fit up against that, which should move it forward a bit.

Thoughts?  Suggestions?

[grumpin]

My first thought was something in the receiver so you can take it out when you want. Then you mentioned what you saw.

If that will hinge out of the way that would be great!

I have the rear mounted spare tire carrier on my Bronco. Sometimes it's a pain, but worth it. I would lose a lot of room with it inside.

My wife's Suburbans spare is mounted inside, I assume they all are. Never really notice it till I'm trying to put something big back there.

I like the bumper/air tank idea also. You are a motivated individual!

[Gary Lewis]

Yes, having the spare in the bed, along with the large tool box, does take up a lot of room.  So for real use that has to change.

As for motivated, I'm not sure that's the case.  I just have a lot of grandiose ideas.  

[85lebaront2]

Gary, when I had my 1958 F100, I put a front mounted spare tire carrier, but, the 58 had a 6' bed and I never had the bed mount for it. I never had any problems with overheating, but, the radiator on the 58 was bigger than the 80-96/7 trucks have other than the Diesels.

[Gary Lewis]

I thought about a front-mounted spare, but with the winch it would put the spare too high.  And, I don't really want to add that much weight on the front of a truck that is already very nose heavy.

[85lebaront2]

Other than the unsprung mass of the front axle, Darth is the same nose heavy way, I just have a 168" wheelbase and front coil springs so he rides better.

[Gary Lewis]

Well, not quite.  Big Blue has the heavy Warn winch bumper, 12,000 lb winch, and auxiliary battery up front.  And the bumper and winch are well ahead of the axle so not only add weight to the front, but also leverage some off the rear.  So I want my extra weight on the rear.

Speaking of which, I talked to a guy at church that not only has a metal fabrication shop but also has a Jeep he takes off road.  He very quickly picked up on what I was talking about, and suggested that we use 6" square tubing with a 1/4" wall, which will allow them to weld on the towing eyes they plasma-cut out of 1" thick steel plate.

So now I need to get busy and design it.  

[Gary Lewis]

First, before designing it, I need measurements and observations.  And what better place to capture them than here.  But, I welcome your thoughts, comments, and questions.

Current bumper is 76 1/4" wide, 5 1/2" tall, & 7 1/4" front/rear

But the bumper is recessed ~2 1/2" into body, as shown below.

A 6" tube bumper wouldn't recess into the body, but if a 1/4" gap is left between it and the body it would only project 1" further to the rear than current bumper.

Top of current bumper is only 1" below the bottom lip of the tailgate, and is only 1" below the tailgate when it is open.  So anything put on top of the bumper would probably require the bumper itself to be placed lower.

There is 4 1/2" of space from either edge of the tailgate's opening to the outside end of the current bumper.  So, the pivot for the spare tire holder could be put there and clear the tailgate.

But, there is 3" between the bottom of the current bumper and the top of the receiver hitch, so the bumper could be lowered or it could be taller.  But, I might want to take the hitch off for offroading to get more clearance, so don't go too low.

Could put a 2 1/2" angle on the front of the bumper between the body to fill in like the current bumper does, although I'm not sure why other than to reduce gaps.  And, if that's desired I could put similar angle on the end of the tube to close that off like the current bumper does.

Don't forget the license tag.  It is currently recessed into the bumper, but could be on the very back of it.  And, it needs to have lighting.

[Gary Lewis]

A bit more info.  A 76" long piece of 6" square tubing with a 1/4" wall will weigh 125 lbs.  So, by the time the spare carrier is added this will be a significant piece.

And a square tube of that size will create a 10 gallon tank, which is said to be a good size for a system with a York/Techumseh engine-driven compressor.  But I need to remember to put a drain in it.

[Steve83]

Gary Lewis wrote

...a rear bumper that will...serve as an air tank...

I've never liked that idea; and even less since watching an air tank explode a few feet from me.  Even on my SWB Bronco, I was able to find plenty of room inside the frame to put a useful-sized air tank (actually 2).

Gary Lewis wrote

...square tubing that is closed on the ends to serve as an air tank.

Sharp corners (like square tubing) are natural weak-spots for pressure vessels.  I'd avoid that.

Gary Lewis wrote

And the arm for the spare would fit up against that...

Do you mean the swing arm would be the rear-most object on the truck at bumper height when no trailer is connected?  I'd be really nervous about backing into something or getting rear-ended, and damaging that arm.

Gary Lewis wrote

I thought about a front-mounted spare, but...I don't really want to add that much weight on the front of a truck that is already very nose heavy.

Gary Lewis wrote

...the heavy Warn winch bumper, 12,000 lb winch...

My front bumper & winch are heavier than those, and I'm not damaging my front wheel bearings yet, with several dozen thousand miles hauling it around on a 1/2-ton suspension.  This was the previous bumper:



The current one is slightly heavier, though I'm not sure how much:



Your 3/4-ton should have substantially more front-axle reserve capacity.  What does it say on the VC label?

Gary Lewis wrote

..auxiliary battery up front.

I put that in the middle of the chassis under the floor, so it actually helps the CG, and distributes the weight to both axles.

Gary Lewis wrote

...tubing with a 1/4" wall, which will allow them to weld on the towing eyes they plasma-cut out of 1" thick steel plate.

The frame is less than 1/8" thick - it has never made sense to me to add anything more than double the frame's thickness to the frame.  It's just overkill, and unnecessary weight; usually an attempt to make up for a poor design.  My front shackles are on 1/8"-wall square tube inserts, and they've taken the full 12Klbs from the winch.

Gary Lewis wrote

So anything put on top of the bumper would probably require the bumper itself to be placed lower.
...
So, the pivot for the spare tire holder could be put there and clear the tailgate.

If the pivot is outside the t/g swept volume, then the arm can ride inside that volume when the t/g is up.

Gary Lewis wrote

...the receiver hitch...

My truck's receiver was originally a few inches below the bumper, but when I designed mine, I integrated them.  Look at this & the NEXT several:



The design includes integral pivots for future mods like a swingaway, but I haven't built those yet.  The factory swingaway has survived my "exuberant" off-roading style.

Gary Lewis wrote

...I'm not sure why other than to reduce gaps.

To prevent the tires from slinging dirt (or dirty rainwater) up on top of the bumper, or against the front lip of the t/g.

Gary Lewis wrote

...similar angle on the end of the tube to close that off like the current bumper does.

Think about how that will snag things that the bumper rubs against; on-road, or off-.

Gary Lewis wrote

...could be on the very back of it.  And, it needs to have lighting.

Consider a t/g-mounted license plate, like early Broncos.

[Gary Lewis]

Steve - Thanks.  Let me try to address some of your points, but I'll surely miss something:

I'm not looking at all that much pressure in the tank, and I doubt the 1/4 tube will be the fail point.
 Yes, it might fail in an rear-end accident, but the only time it is going to have air in it is when off-roading.

Yes, sharp corners are fail points, but we will be far short of the limits of that tube and its welds in PSI.  If I were to do the welding there might be an issue, but it will be built by licensed welders.

I haven't settled on what the arm for the spare will be made of nor how it will attach, but I do take your point about it being the rear-most point.  However, what I'm envisioning in my mind is that the arm will be made of two pieces of heavy angle that lay against rear of the bumper at the top and bottom of the square tubing and will be hinged with top and bottom bolts on the right end of the bumper.  In the center the top angle will have a vertical square tube for the spare tire.  And there will be some kind of latch there to ensure the arm can't swing, nor can it move up and down - and I've not worked that out yet either.  Perhaps a bolt?

But, when the arm is swung to the traveling position it will be up against the bumper.  So when backing into something that is bumper high there won't be any damage.  However, if the "something" is tall enough to hit the spare then there will be damage, probably of the tailgate.  

I'm not worried about overloading the front axle.  But I do know that I have a lot of weight up front and for traction I'd rather not put more up there.  And, since the ride is brutal due to the rear springs being so stout I want to put some of the weight in the rear.

My auxiliary battery is in the stock position right now.  It may be that it'll have to be relocated when I put the EFI on given all the things that have to go on the driver's fender, but we will see.

The reason for going to 1/4" walls on the tubing isn't because it is a bumper or because it is an air tank, but because we are going to weld the tow eyes on it.  My friend's fabrication shop has built a number of things for off-roading, including trailers, bumpers, etc, and they've learned that the tow or recovery eyes need to be welded to 1/4" steel to prevent the bumper from bending.  So it certainly is overkill compared to the frame, but the thickness is needed.

I like your bumper design.  And I might go that way.  In fact, I think I could still add the spare tire mount to it, but couldn't get into the storage area w/o swinging the tire out of the way - at least in the design in my mind's eye.

However, that would do away with using the rear bumper as an air tank.  And, it looks like it would raise the height of the hitch significantly, and mine is already very high.  Plus, it would prevent me from removing the hitch to increase the rear departure angle.

Hmmm, I'll have to think about this....

Yes, I see how the filler would help keep the yuk down.

On the tag, I'm thinking that the spare would block it if it were on the tailgate, and I don't want to mod the nice 'gate that's on there.  But, why not put it in the center of the spare?  I could design a piece that is held in with the lug bolts and has a connector down at the bumper for the lights.

So, thanks for the suggestions.  They've given me a lot to think about.  

[Steve83]

Gary Lewis wrote

...I doubt the 1/4 tube will be the fail point.

It certainly won't fail the first 100x you air it up, but even 1/4"-wall steel will fatigue.  And the corners will fatigue much faster than any other shape.  So for any pressure vessel, it's a shape to avoid.

Gary Lewis wrote

...the arm will be made of two pieces of heavy angle that lay against rear of the bumper at the top and bottom of the square tubing...

That would certainly fit around the square tube, and it would probably carry the dead weight of the spare.  But it would be very weak in the fore-aft direction, like when braking or accelerating, or when backing the spare into something or being rear-ended.  It wouldn't resist the torque applied to the arm by the weight of the spare being so far above the arm.  A thinner-wall rectangular tube would be much stronger & lighter.  It would be more-crushable in an impact, but I'm still saying it belongs on top of the bumper.

Gary Lewis wrote

...there will be some kind of latch... Perhaps a bolt?

That would be the most-difficult latch to operate; most-susceptible to rust or even a tiny burr on the threads causing binding; high-wear on the threads causing looseness or thread-stripping...  I prefer a spring-loaded latch (like factory), and in this application, it would be easy & cheap to build a reliable one.

Gary Lewis wrote

...the ride is brutal due to the rear springs being so stout I want to put some of the weight in the rear.

A really quick, easy, cheap way to smooth the ride is to clean & grease the leaves.  Jack the frame up so the axle hangs, spreading the leaves, and use a prybar to get in-between them.

Gary Lewis wrote

...the tow or recovery eyes need to be welded to 1/4" steel...

I was actually talking about the 1" tabs being overkill.  If you want/need that size/shape, a 1"-wide rectangular tube with 1/8" walls is enough, at a fraction of the weight/cost.

Gary Lewis wrote

...couldn't get into the storage area w/o swinging the tire out of the way...

Right, but mine has been that way for decades, and it has never been a problem.

Gary Lewis wrote

However, that would do away with using the rear bumper as an air tank.

Right - I'd put the tank(s) in the frame, between the axles.

Gary Lewis wrote

...it would raise the height of the hitch significantly, and mine is already very high.

Long-drop draw bars are becoming common, affordable, strong, & safe.

Gary Lewis wrote

... removing the hitch to increase the rear departure angle.

Since it would be integrated so high, it wouldn't need to be removed.  And the draw bar could simply be flipped up or sideways.

Gary Lewis wrote

But, why not put it in the center of the spare?

That's another good option, if the tube is an air tank, and can't have the plate mounted to it.  But if it's NOT a tank, the plate & lights are easy to mount to the bumper face.  I used the factory lights.

Gary Lewis wrote

...a connector down at the bumper for the lights.

...or just run the wiring through the swing arm, up the spare mount, to a quick-connector there.

You've got lots of options right now - once it's built, you'll be stuck with your choices, so take some time to make the ones that suit your purpose best.  It took me a couple years designing my first 2 bumpers on paper before I started building them.  The current front bumper was quicker, even though it's more-complex, because I used CAD.

[Gary Lewis]

Steve - You've given me a lot to think about.  Thanks.

I will be drawing something up on TurboCAD.  But I'm still struggling with what it will be.

However, I do agree with your thought that the angle will not handle the fore/aft forces.  In fact, I was thinking that as I typed it last night, but just didn't think it through fully.  As I look at it in the light of day, there would be plenty of room on the top of the bumper for a piece of square tubing, even as large as 4" if needed, and still clear the tailgate.  Assuming it is hinged on the part that sticks out past the body.

As for the latch, while I like yours, I want something more secure.  I don't want there to be a chance that the whole thing will get loose and swing, regardless of what happens.  And, I don't want there to be any up/down movement when underway.  So, perhaps a large wing screw, maybe in addition to a latch?  Fastenal has wingscrews to 1/2-13 with a 2 1/4" wingspan.  I don't see one in stainless, but I could easily make one out of a stainless bolt and a stainless wingnut, possibly even leaving the hex head of the bolt showing for extraction if necessary.  But, with a bit of anti-seize on it I doubt there'd be any problems getting it out.

As for the ride, the springs are fairly new and still have their nylon slippers.  (The PO put LOTS of new components on, including front & rear springs, front/rear Torsen diffs, and so on and on and on.)  It is just that there are 7 leaves, and there's no weight back there.  So, when the dust settles on what goes where and how much load there will be I'll probably remove some leaves and then put either overloads on or air bags.

And on the tow eyes, the fab shop already has those made.  I've not seen them, but will talk with him about how big they need to be.

Last, I'm not sold on the integrated hitch.  But, there's merit to it from the standpoint that it would attach to the frame MUCH more securely than the rear bumper does.  My current hitch bolts onto the frame with three 1/2"-13 bolts per side, and looking at it I see that even if I want to keep it I could run a 1/4" angle forward from the bumper and sandwich it between the frame and hitch.  So, I am thinking about it.  

[Steve83]

Gary Lewis wrote

But I'm still struggling with what it will be.

I usually start on paper, and once I find a basic design that makes sense and can be built, I start refining it on the computer.  But I always start with the strongest method I can imagine to attach to the existing truck frame horn, withOUT modification (no welding or cutting, and new holes only when absolutely necessary).  Then I extend that enough to put my bumper beam where I need it, for the rest of the design to work.

Gary Lewis wrote

...I want something more secure.  I don't want there to be a chance that the whole thing will get loose and swing, regardless of what happens.

Look at how rinky-dink the old Bronco swingaway latches were, and they were designed by professionals!  But they worked well enough for DOT and all the lawyers.

Gary Lewis wrote

And, I don't want there to be any up/down movement when underway.

That's easy, with a structure near the latch that doesn't move, but captures the swing arm so it can only move out of the latch when the latch is activated.  IOW: a sturdy C that fits snugly around the swing arm, mounted solidly to the bumper.  Or a pin fixed horizontally (fore-aft) to the arm that fits into a hole on the bumper face.

Gary Lewis wrote

So, perhaps a large wing screw, maybe in addition to a latch?

The more "latches" you have, the easier it becomes for at least one of them to become misaligned due to age (wear) or impact.  Use 1 latch, and build it right, and let that be it.

Gary Lewis wrote

Last, I'm not sold on the integrated hitch.

More food for thought: modern F-series rear bumpers are just decoration on the hitch receiver.  The receiver IS the real bumper structure, and what you see is just cosmetic: thin chromed steel, or treadplate-molded plastic.

[First Today]

Hey Gary and everyone.

Have you thought about using the factory swing away spare tire gate that was on the broncos?
Make sure you get the re inforcement plates that go behind the body.

I put one on my 65 f100 big body bronco i had made years back. I cut the roof  and tops of the doors off,  installed a rollbar, and added an 80's bronco spare tire gate. I didnt have the re enforcement plates, but had no issues with a standard tire on it.

[Gary Lewis]

I'd never thought of that.  In fact, I'd never really stopped and thought how similar the pickups and Broncos are back there.

Here's a shot of Espy sporting that carrier, and it looks like it would fit quite well.  Interesting.

I'm not sure I like it as I don't think I want to drill the body on Big Blue.  But, it is certainly an option that I should consider.  Thanks!

[grumpin]

First Today wrote

Hey Gary and everyone.

Have you thought about using the factory swing away spare tire gate that was on the broncos?
Make sure you get the re inforcement plates that go behind the body.

I put one on my 65 f100 big body bronco i had made years back. I cut the roof  and tops of the doors off,  installed a rollbar, and added an 80's bronco spare tire gate. I didnt have the re enforcement plates, but had no issues with a standard tire on it.

Good idea!

[Nothing Special]

Gary Lewis wrote

.... The reason for going to 1/4" walls on the tubing isn't because it is a bumper or because it is an air tank, but because we are going to weld the tow eyes on it....

I'm late to the party (again) and trying to catch up a little.

One thing to maybe keep in mind is that a lot of organized runs don't allow welded recovery points.  They need you to have recovery points that are bolted to the frame.  Yes, welded points can be strong, but they can also be weak but look strong.  Getting it welded by a licensed welder should minimize that risk, but the organizers of the run don't need to accept that.

On my Bronco I got around that by welding my bumper to my recovery points.  The plates that bolt to the frame come through holes in the bumpers, so the clevis is attached to a piece that is directly bolted to the frame.  And then the recovery points end up being the bumper mounts as well.


And on the Bronco spare tire carrier, it seems to me that I've seen a lot of pickups with floppy bed sides.  Hanging all of that weight with that much leverage seems risky in that area.  (Unless the latch carries much of the weight.)

And speaking of latches, I wish I had a picture, but on the CJ5 I used to have I built a swing-away tire carrier mounted to the rear bumper.  For the latch I used an over-center toggle latch like this that pulled the free side of the carrier into sort of a "V" notch.  It was pretty quick and easy to work (although it did frequently take one hand to hold the "loop" in position while working the handle with the other hand), and it held the carrier pretty securely.  Just another "what if" to throw in the hopper.

[Gary Lewis]

That's good info.  I wasn't aware of the issue with events and tow eyes, but that makes sense.  Do you remember what ones you used?  I'll look around, but if you had a recommendation that might help.

Taking a quick look at Big Blue, I can see how the eye bracets could bolt on and the stem of the eyes pass through the bumper, thereby attaching the bumper to the frame.  I think I like that approach.  And, if the bumper also bolted to the hitch mounts then it would be extremely solid.

As for the swing mount, I'd wondered about the strength of the bed side.  I really like the idea of having the mount attach to the bumper as that way it can be very stout as well as leave no holes in the bed.  And, I like that latch.  Lift the swing arm a bit to get it into the V, and then clamp it down with the latch.  Won't go fore/aft nor up/down.

Thanks!

[Nothing Special]

Gary Lewis wrote

That's good info.  I wasn't aware of the issue with events and tow eyes, but that makes sense.  Do you remember what ones you used?  I'll look around, but if you had a recommendation that might help....

And, I like that latch.  Lift the swing arm a bit to get it into the V, and then clamp it down with the latch.  Won't go fore/aft nor up/down.

Thanks!

I made my own tow eyes.  I started with some 1" thick x 4" tall bar stock and milled away everything that didn't look like a tow eye or a bumper mount.  I used 2"(?) x 4" C-channel for a bumper and milled holes in it for the tow eyes to poke through and welded the bumper to the tow eyes.  The tow eyes are... stout.  I probably wouldn't recommend using that much steel for them.  1/2" or even 3/8" thick is probably plenty.  (And they aren't still 1" thick in the tow eye section, I had to mill that thinner to fit a standard clevis over it.)  But I'm happy with what I have.  Below is a picture of the finished product.

And on my Jeep the "V" pointed backward, so the carrier just swung into it, no lifting required.  The clamp pulled the arm forward, to bottom it in the "V" and the taper on the top and bottom of the "V" kept the free end of the arm from moving up and down.  And calling it a "V" is maybe misleading.  there wasn't a lot of angle to the top and bottom. Just enough to kind of wedge the arm in place.