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Old 12-16-2014, 10:44 AM   #1
gpt
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Taking the bikes along

i checked out the 'official' Airstream bike rack but when i noted that it had support structure that would be in contact with the rear of the trailer, on the trailer skin, i passed on that notion.

having the necessary welding equipment, i went to work fabricating my own receiver. i already have a quality Yakima bike rack so the rest was quite simple.

if you have the equipment, build your own a simple satisfying project and one guaranteed not to bung up the outer skin.
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Old 12-16-2014, 10:59 AM   #2
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Nice work; nice photos!
(although AS does discourage rear receivers, yours looks well done)
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Old 12-16-2014, 11:17 AM   #3
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I'm not certain about this (don't use a bike rack), but I believe the reason Airstream attaches their bike rack to the body of the trailer is because they don't want all the load on the frame. The bouncing load applied only to the frame can potentially cause frame/body separation.
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Old 12-16-2014, 11:38 AM   #4
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actually the 'official' Airstream bike rack attaches to the frame rails in pretty much the same location i used. i did look this over pretty carefully before proceeding.

i would guess they discourage receivers because in some states you can actually tow another unit behind your trailer. in this case, it would be a bad idea as the materials i used are not heavy enough for that sort of application.
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Old 12-16-2014, 02:45 PM   #5
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Quote:
Originally Posted by gpt View Post
actually the 'official' Airstream bike rack attaches to the frame rails in pretty much the same location i used. i did look this over pretty carefully before proceeding.

I would guess they discourage receivers because in some states you can actually tow another unit behind your trailer. in this case, it would be a bad idea as the materials i used are not heavy enough for that sort of application.
Whereas the vertical load would be the same with your mounting, the Airstream rack is tied in to the trailer up high, which prevents twisting. Think of every time you put the brakes on, with the centre of gravity of the bikes and carrier quite a bit higher than the receiver. The bikes come forward and apply a bending moment, or twist, to the receiver. If the rack extends rearward of the receiver, there is a bending moment in the other direction due to the lever, both in static mode and amplified when you go over a bump. If you have very light bikes it may not be a problem, but that is the concern regarding separation of the body, and the Airstream mitigation for that risk.

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Old 12-16-2014, 04:42 PM   #6
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well, if a Yakima bike rack can separate the frame from the body of the trailer, i'd have to be wondering just what sort of trailer i am towing. having used this Yakima rack on several vehicles, it actually bolts tight inside the reciever, i am not in the least concerned about any of this. if you think you can 'twist' 1.5" square tubing, wow, you are much stronger than i will ever pretend to be.

with the trade-off being a support mechanism on the Airstream rack in constant contact with the exterior skin of the trailer, i do believe i have a way better solution then wearing nice divots into the stern of my trailer.

in fact, i talked with another Streamer this past fall who had a rack fabricated to carry his motorized scooter in much the same position, no problems for him either.
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Old 12-16-2014, 05:20 PM   #7
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No, I don't think you can twist the square tubing. I think that the torque applied to the square tubing by the offset load will be transmitted quite efficiently to the single point mount you have designed. Those rails can flex and deflect. The body won't. Over time, that is what can cause separation. If you have very little load on the rack, and it isn't extended out to the rear, there will be less of an effect. But the information is presented so that you can at least consider the failure mode and know why Airstream uses a bike mount with a top brace. It isn't for style.
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Old 12-16-2014, 05:24 PM   #8
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Yakima bike racks load capability is why I purchased mine, my bike is lightweight aluminum but the wife's electric with batteries makes it twice as heavy. Put it on my Fit and have total confidence it isn't doing damage. Only additions I had to make was a trough to push the electric across and a cross bar as Yakima engineers didn't consider putting a women's bike on it;( By tightening the mounting bolt instead of a pin it stops it from rattling, but I have noticed the bolt will loosen on a long trip.
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Old 12-16-2014, 05:36 PM   #9
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I haven't looked at this closely but my understanding is that the rack that AS recently sanctioned is designed in a way that the load is not all carried by the trailer frame bur also the body.

Prior to that, they did not recommend carrying bikes on the back of the trailer with a standard hitch. I believe the manual with our trailer specifically mentions this.

When we bought our trailer (used) it had a 2" hitch receiver welded to the frame. My initial thought was "Great, I will use this for our bikes." After reading a great many comments advising against doing that, I cut the hitch receiver off!"

In looking closely, I see evidence of some minor damage to the back end of our trailer that I think might have been cause by that hitch.

I carry the bikes with a front mounted receiver on our truck as I did for many years with our previous trailer.

Not at all saying you will surely cause damage, but I would keep an eye on things - those bikes bouncing up and down bad there on a cantilever arrangement can impose significant loads.

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Old 12-16-2014, 05:53 PM   #10
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the current AS rack bolts to the frame with 3 bolts/side in pretty much the exact same way my fabrication does. i looked at it closely at the dealership before i decided to proceed. the AS rack ride above the rear bumper but requires two contact points from the rack to the back of the trailer body. having the rack rubbing on the outer skin, i didn't think was a great idea. any up and down movement is not going to be any different than that i might experience. front to back, the skin of the trailer is going to take a beating.

while my solution will not support towing of another trailer or whatever, as is common in several western states, i don't believe it imposes enough deflection on the frame to warrant concern. if you check out the frame rails, they are substantial C channel steel. i would guess the Yakima rack is all of 20#s and the off road bikes perhaps 30#/ea. so a grand total of 80#s causing the frame to separate from the body??? if that turned out to be the case, i have definitely purchased the wrong trailer.

my circle of friends includes several streamers who commonly off road with their trailers and i would suspect bouncing around down the dirt roads they travel creates far more strain than this simple bike solution is capable of providing.

as i said earlier, trailer manufacturers don't like to see receivers on the back of their trailers for fear that someone is going to hook up another thing to tow along, a PWC comes to mind. with my solution, that would be a really bad idea as this does not come close to even a class III hitch.

i also believe there is some confusion as to how the AS bike carrier attaches to the trailer. in fact it is bolted directly to the frame in pretty much the exact position of my fabrication. the difference is to prevent fore and aft movement of their rack, it relies on direct contact with the stern of the trailer, right on the exterior skin, by two arms that are extended form the rack forward.

hope this helps you visualize what is going on with the frame members in either application.
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Old 12-16-2014, 06:01 PM   #11
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I've always wondered why airstream didn't build a receiver and a bike rack. It could be a unique shape that required an airstream specific/branded bike rack. Then it couldn't be used for a purpose that would do damage. And they could and would charge a lot for it!


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Old 12-16-2014, 06:06 PM   #12
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gpt,

None of us really disagree with anything you have said, but you seem to be rather defensive of your ideas and bike rack installation (a very nice job I might add).

However, that being said, Airstream for years would not allow any bike racks on the back of their trailers for fear of frame separation, because it was a big problem in the past, especially with rear bath models. Airstream trailers are built quite a bit different than most other travel trailers in that the frame is rather flexible, and relies on the strength and ridgidity of the body to form a monoque (SP?) structural unit like an airplane fuselage.

It has just been in the last few years, and under pressure from customer demands, that they came out with their bicycle rack. The way they engineered it to distribute the acceleration load of bouncing down the road with 100+,- pounds suspended behind the trailer was to mount it to the body as well as the frame.

We are not trying to tell you your mount will not work. It will work. However, over time, with many miles, it MIGHT cause a frame/body separation. It has happened in the past, and we are just tying to get you to understand the potential problem.

With Airstreams like most things, you can get away with almost anything, for a while.
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Old 12-16-2014, 06:26 PM   #13
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The Airstream shell/frame are designed to support each other, they work together as a monocoque structure. Frame separation has been common when even 80# are loaded on the back of the frame, with no attachment to the shell. That is because the 80# is first multiplied by it's position behind the axle, and severely multiplied again when going over rises and dips in normal roadways.

Understanding this, you did not buy the wrong trailer, it just has it's limitations because of it's semi-monocoque structure. It saves weight and contributes to the fine handling characteristics of your Airstream.

I think you could add struts back to the trailer similar in position and design to the Airstream rack and avoid the potential problem. This would hold the rotational effect of the bikes going over roadway dips and thereby minimize the multiplied load on the Airstream frame.

The Airstream rack works very well, we have traveled extensively with it without any problems.
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Old 12-16-2014, 07:44 PM   #14
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I can tell you my experience for what its worth....

I just re-attached my shell to my frame after fixing all the damage from rear rot and frame separation. My first observation as I disassembled the rig is how light weight (errr weak construction) the frame is. Super flexible- definitely not "stout" and/or rigid by any stretch. I had to jack up, (or down) each section of the frame to line up with the shell around the perimeter.

When it came to the rear, I had to literally jack up the frame to meet the shell. Hence, the "shell" holds up the frame. The frame does NOT hold up the shell. And at that, the part of the shell that holds up the frame is 1/16th aluminum channel bolted across the rear cross member.... Not super structural.

Inland Andy has quoted the engineering specs on the multiples of weight impact due to the leverage principles, that a simple 50 lbs has when bouncing over the road. It makes perfect sense to me- unless you tie that weight back into the shell, it could definitely be adding a significant load to that aluminum channel holding the frame up.

I see the design of the Fiamma is to keep the load on both the shell and the frame, as to not isolate the load to the frame.

Although I'm not a fan of the way the Fiamma blocks the bumper storage and rear hatch, the design looks to be the proper way.

Being that I have rebuilt my frame, floor, and reinforced the shell connection to hold the frame up, I still will NOT install a hitch style carrier. It may very well work for as long as I need it, or may very well lead to damage, but I see the weakness in the Airstream construction and knowing what I know now, see a longevity issue. I will do the Fiamma if I have to, but have my eye on the Arvika tongue hitch... although I have a family of 5, so might need to do both.

Your install definitely looks tight. I love the idea and wish it would work for me. Hope it works for you.
Mic
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