Spare tire swing arm capacity

[Hayes]

What are folks thoughts on the effective load capacity of a the typical bumper mounted spare tire arm?

I'm considering using Gamiviti's spate tire hitch receiver and a drop to mount a bike rack to my BIOR spare tire arm. This would be the swing arm, the spare tire (16" alu rim and 295/75r16 tire), the receiver, a 35 lb bike rack, and a couple 30 lb bikes.

Too much for the spindle?
Well within the limits of the spindle?
Any intrepid engineers who can succeed in translating the load rating of the spindle to the above stated load (lever arm and all, is it shear? Etc?)
Alternatively, has anyone rocked a similar setup without catastrophic failure?

Thanks for your time.

 

[Live to Ski]

Ok, often thought about this exact question for a future addition to the rig (depending on health).

1. spindle is probably your least concern. Look at how the load is transferred to the spindle (the rack). Bending/torsion will be your issue here. There is a lot of bending load on that arm due to weight of tire, bikes, rack, load distances, etc.

2. besides the static loads, fatigue is of more concern due to highway seams (high frequency, lower load as compared to offroad).

3. Besides knowing loads (easy part), need to know the a) arm materials, b) cross sections of all relevant structures.

4. Potential easy way out: rig up load straps that run from the most aft part of the bike rack, to the rig (probably roof area, that is roof rack or ?). Probably want 2 straps. tighten those bad boys. This will limit deflection, thus lower stresses. You will most likely not have catastrophic failure (if at all) with this option, and probably see indication of impending failure. You can then weld appropriate brackets at the problem area(s) to your heart's content.

If 4 above is off the table (don't' know why) members who have 1) solid CAD model, 2) cad program (solidworks, pro/e, or ?), 3) cad program analysis package can make more exact determination. Hand calcs would get you close. Note these options would be expensive unless you have experience doing those.

 

[Hayes]

Yep.
These are my concerns. I don't think (recognizing the absence of quantitative analysis here) that there is any risk of failure with any reasonable static load on a closed and latched swing arm--it's all transferred to the bumper.
It's the resulting load that results from rattling down those washboards or bashing the occasional step with extra weight on yhe lever (more torque) that I'm uncertain of.

I think it has been clearly demonstrated right here on MUD that a well made bumper and spindle-mounted carrier can sustain a 35" tire and wheel (not an insignificant load) through some pretty dynamic conditions. I rocked said gear on my 80 for a decade of rattles and bashes without failure.

I've poked around at torque calculations based on estimated weight and lever lengths, but I'm not convinced this is the right question in regard to spindle load rating, or even that the spindle itself is the the actual failure point. Really, I think an empirical test might be most relevant. What have folks carried in regard to water/fuel cans? Multiple spares?

Ok, often thought about this exact question for a future addition to the rig (depending on health).

1. spindle is probably your least concern. Look at how the load is transferred to the spindle (the rack). Bending/torsion will be your issue here. There is a lot of bending load on that arm due to weight of tire, bikes, rack, load distances, etc.

2. besides the static loads, fatigue is of more concern due to highway seams (high frequency, lower load as compared to offroad).

3. Besides knowing loads (easy part), need to know the a) arm materials, b) cross sections of all relevant structures.

4. Potential easy way out: rig up load straps that run from the most aft part of the bike rack, to the rig (probably roof area, that is roof rack or ?). Probably want 2 straps. tighten those bad boys. This will limit deflection, thus lower stresses. You will most likely not have catastrophic failure (if at all) with this option, and probably see indication of impending failure. You can then weld appropriate brackets at the problem area(s) to your heart's content.

If 4 above is off the table (don't' know why) members who have 1) solid CAD model, 2) cad program (solidworks, pro/e, or ?), 3) cad program analysis package can make more exact determination. Hand calcs would get you close. Note these options would be expensive unless you have experience doing those.

 

[Skidoo]

I have the early Slee single long arm that puts tire in center. For me the spare tire grabbing coming down steep ledges worries me more than the load I put on it. Tire deflects quite a bit. By the way those spindles are same as used for front of cars and light trucks and have a 1000 lbs or more on them. On cars some interesting forces on them in high speed turns or potholes.

 

[suprarx7nut]

I've got the BIO rear carrier with tire. I can't see it being an issue, whatsoever. I have the plastic contact plate in the center of the bumper shimmed up so that the arm is pulled into contact while latched closed. The arm deflects a tiny amount to come into contact (maybe 1/32"). In that scenario there is effectively zero load on that arm, no matter the weight, when it's closed. (You'd get a small deflection and eventual creep in the arm if you had a huge amount of weight in the center of the arm, but no problems should arise given what you're describing.

The spindle bearing and the arm are incredibly stout. Without doing an FE analysis on it, I wouldn't hesitate to load it up. I would, however, avoid driving with the arm loaded while the arm is open and just cantilevered off the spindle.

I'd also recommend shimming the plate like I did. It's completely removed any clunking noises while driving and feels wonderful to latch into place. It's rock solid. As it was from BIOR there was maybe 1/8" clearance when latched. It worked as is, but I prefer the shim to create contact when latched.

 

[Live to Ski]

As mentioned above and in my post.....don't worry about the spindle. Those are typically derived from front wheel spindles.....you will have a hard time breaking those.

Also, as mentioned, the static loads will not be the issue. It will be fatigue (whether off road driven frequency, or highway driven frequency). You would be surprised at how loads interact with highway slap seams (concrete, n/a for asphalt) at speed. In that world, one has to design the structure such that it's natural frequency is well away from the driving frequency (slab perior/speed)

What is the hesitation of going with the hardware you want, and running load straps out to "stiffen up" the cantilever bike rack, which will be way out there (relatively speaking)? Cheap, easy, robust.

That's my story and I'm sticking to it

 

[Hayes]

I've done exactly that with the BIOR plastic contact plate--as you described, it eliminated the clunk I was getting.

I've got the BIO rear carrier with tire. I can't see it being an issue, whatsoever. I have the plastic contact plate in the center of the bumper shimmed up so that the arm is pulled into contact while latched closed. The arm deflects a tiny amount to come into contact (maybe 1/32"). In that scenario there is effectively zero load on that arm, no matter the weight, when it's closed. (You'd get a small deflection and eventual creep in the arm if you had a huge amount of weight in the center of the arm, but no problems should arise given what you're describing.

The spindle bearing and the arm are incredibly stout. Without doing an FE analysis on it, I wouldn't hesitate to load it up. I would, however, avoid driving with the arm loaded while the arm is open and just cantilevered off the spindle.

I'd also recommend shimming the plate like I did. It's completely removed any clunking noises while driving and feels wonderful to latch into place. It's rock solid. As it was from BIOR there was maybe 1/8" clearance when latched. It worked as is, but I prefer the shim to create contact when latched.

 

[abuck99]

Ive got the bior rear bumper with dual swing outs. I you probably could add another 100-150+ lbs to the swing out with out issue. The challenge may be with the added weight and how that contributes to the bumper wiggle/flex. With my spare on the back i get get some pretty decent flex and movement at the corner of the bumper out to the end of the wing, which transitions through the frame and you can feel it through the drivers seat especially on segmented concrete highway. Add more weight positioned further out would make it worse.

 

[Aggie04]

I've got the BIO rear carrier with tire. I can't see it being an issue, whatsoever. I have the plastic contact plate in the center of the bumper shimmed up so that the arm is pulled into contact while latched closed. The arm deflects a tiny amount to come into contact (maybe 1/32"). In that scenario there is effectively zero load on that arm, no matter the weight, when it's closed. (You'd get a small deflection and eventual creep in the arm if you had a huge amount of weight in the center of the arm, but no problems should arise given what you're describing.

The spindle bearing and the arm are incredibly stout. Without doing an FE analysis on it, I wouldn't hesitate to load it up. I would, however, avoid driving with the arm loaded while the arm is open and just cantilevered off the spindle.

I'd also recommend shimming the plate like I did. It's completely removed any clunking noises while driving and feels wonderful to latch into place. It's rock solid. As it was from BIOR there was maybe 1/8" clearance when latched. It worked as is, but I prefer the shim to create contact when latched.

Can you post pics of this?

 

[suprarx7nut]

Can you post pics of this?

Sure. I just grabbed some in the garage with my phone. Not the best picture quality, but hopefully shows it well enough. I had to take the pics a couple times to get the right angle. The arm movement is VERY precise so I was able to give it a very, very small amount of clearance. The clearance being that small makes it tricky to photograph.

You can see the washers that are shimming the "contact plate". I used some 1/4-20 button head screws I had lying around, but I should really switch them out with longer flat heads. I'll do that next time I make an order with McMaster.

I also need to get matching hardware for the toggle clamps. I liked the button head, but didn't have enough in the garage to use only button heads.

 

[Hayes]

Test fitted the rack. Haven't pulled the trigger.
The Kuat rack is far lighter than it looks. It specs out at 32 lbs. Figure 2 bikes weighing 30 lbs each.
The height of the bikes is initially a bit shocking, but I'm not convinced it's a problem. The guy at the rack store thought the whole setup was really cool.
Or is it loco?

Thoughts.

 

[creakycruiser]

Test fitted the rack. Haven't pulled the trigger.
The Kuat rack is far lighter than it looks. It specs out at 32 lbs. Figure 2 bikes weighing 30 lbs each.
The height of the bikes is initially a bit shocking, but I'm not convinced it's a problem. The guy at the rack store thought the whole setup was really cool.
Or is it loco?

Thoughts.

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Holy crap! That's awesome, lol!

It's like your 100 is saying, "Look at my bike. This is my bike. Hold it high."

 

[Hayes]

Receiver tube welded on to the arm itself.

 

[geanes]

Receiver tube welded on to the arm itself.
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THAT'S what I'm talking about! Well done. What are your impressions thusfar? I've got a BIOR dual swingout bumper and LOVE this idea of welding on a receiver to the arm.