Bumper Bike Rack as part of rear frame upgrade

[jcl]

Originally Posted by AlbertF

I would not be concerned about the rearward shift of centre of gravity. Instead, I would be concerned about stressing the connection between the frame and the shell.

As anyone who has dealt with tail droop on a 1970s Airstream knows, the frames are light and relatively flexible, and the shell actually holds the frame up. The connection takes the form of small bolts connecting the shell to the perimeter of the plywood floor, and bolts attaching the plywood floor to the frame.

That is the reason the custom Can Am bike racks and the Fiamma bike racks are attached to the shell. The shell carries the weight of the bikes, and the connection to the bumper is primarily for stability.

In both the Fianma and the Can Am designs, the weight is not carried by the shell, this is incorrect. The weight is carried at the lower attachment, the bumper. The top attachments use struts with pins, they are not rigid in the vertical plane, so they can’t carry vertical loads. See the photos in the attachment in this thread.

What the top attachments do is restrict fore and aft movement of the rack, which reduces the bouncing of the rack when loaded. That bouncing results in rotation/bending at the lower seam of the shell, essentially the same as flexing a coat hangar back and forth every time you go over a bump in the road.

There is nothing wrong with building a custom bike rack mount, from a load carrying perspective, but it is a cantilever and adding the top struts would greatly improve the design. This is separate from the potential stability issues risked by placing a load far to the rear of the axles.

[OTRA15]

Originally Posted by wulfraat

I think the OP appears to have his eyes wide open.
. . .

Agreed, and you are clearly a well-informed Airstream user who has done admirable due diligence for all your projects IMO. Well done.

The novice Airstream owner, however, will benefit, at first, from not "pushing the envelope" with modifications to his or her Airstream IMO. In the limited time available this afternoon, after perusing the Fiamma search results linked in Post #3, these sources of Airstream's thoughts on a rear bike carrier are good enough for me:

* Colonial Airstream -- "only factory approved bike rack for an Airstream."
https://www.colonialrv.com/blog/airstream-bike-rack/
* Airstream YouTube video linked below at 00:30 -- "total weight . . . still under 100 lbs."
* "The official Airstream bike rack is here."
http://vogeltalksrving.com/2012/02/a...-bike-carrier/

Obviously Airstream has been silent on whether folks are free to add heavier and longer rear bike racks, but arguing over this theoretical possibility is surely a fool's mission IMO.

Have a good weekend.

Peter

IMO -- FYI -- and FWIW

PS -- Airstream video -- see at time stamp 00:30:
[click on URL at top of frame to open up a new window with Full Frame etc. options]

https://www.youtube.com/watch?v=uQXo-AS1xcM

PS2 -- FYI -- and FWIW -- another rear hitch mounted bike rack thread:
http://www.airforums.com/forums/f464...er-174590.html

. . . where franklyfrank has expressed a similar opinion as in this thread.
[click on orange arrow in quote to go directly to that post:

Originally Posted by franklyfrank

This is the kind of post that really gets under my skin.
I have designed fabricated and installed my own bike carrier system on a 30' AS. Used it on a 2013 for 4 years and on my 2017 30' Classic close to another year. The entire setup weighs a bit over 120 LBS and I simply stabilized it with a machined to size receiver. It doesn't sway bob or anything. I generally travel at 72 MPH on interstates when weather and traffic conditions allow. I travel through Chicago, Atlanta, Miami regularly where maneuvering is challenging and had my share of emergency maneuvers without and sway issues whatso ever. And I don't use a ProPride or a Hensley. I use a Blue Ox.
So I can confidently state that there are other very safe ways to tackle the bike Rack issue as I have proven it over 5 years o use.
I don't have an ax to grind I am not into selling anything. I am relating real world experience for others to draw on.For you the keep saying But, But, But is down right ignorant. Had I experienced one scary moment with my installation it would have been removed pronto.

PS3 -- This quotation is copied here as a courtesy to franklyfrank.

[OTRA15]

Originally Posted by gklott

Would appreciate the help by posting a link to the actual Airstream design or rear loading parameters that you mention.
. . .

Please see new post.

Have a good weekend, and Happy Trails!

Peter

[jcl]

Originally Posted by franklyfrank

...
And to suggest that only safe way to do a bike rack is to install a Fiama or have Can Am install one is down right ridiculous.

Not necessary. You are trying to build a straw man. It was pointed out to you in a previous thread that if you installed the top strut (as used by Airstream and Can Am) you would improve your custom design, and match their functionality. It wouldn’t be difficult. It would probably take less time than making your repeated posts on this subject.

[OTRA15]

Thank you, jcl, for the excellent points in your two recent posts, and for your polite and mature adult tone.

[sgschwend]

Here is a picture of the storage area. Note the hitch is not visible when looking under the cover. As long as you can avoid wacking your shin on the hitch it is a nice way to maintain the storage space and have almost everything out of sight.

[wulfraat]

Very nice.

[franklyfrank]

Originally Posted by wulfraat

I think the OP appears to have his eyes wide open.

When I located 300lbs of lithium batts and related gear under my rear queen bed in my 2017 30’ international I did extensive homework to include securing airstream frame layout design schematics... and part of my due diligence including speaking with airstream and one of the most experienced airstream commercial uplifters in the country who often change out frames for commercial applications....

I had several dialogue with both parties and asked if they could produce airstream “design parameters”. They could not produce them for me and airstream also indicated that airstream engineering have not done any formal frame / shell load testing of said design parameters.

So all the conjecture about weight aft of the rear axles is hearsay without data or real world test results. Putting a bike rack on a 30’ trailer is not the same as loading 300lbs of gear on the back of a 25’ trailer like my fellow Quebecer we did so one can not compare the two. Each instance of loading a particular trailer with any kind of weight anywhere in or on the trailer should be treated as an individual test case.

Great comment and good analogy.
Thank you

[pteck]

I'm in the midst of fabricating my receiver as well. This is a perfect relevant thread.

I'm taking a different strategy, which is to mount a receiver tube underneath the airstream bumper.

A few reasons:
1) Don't want to change the aesthetic of the AS.
2) The under bumper receiver allow me the use of various bike racks and to be nestle the rack itself as close to the rear bumper as possible to minimize overhung leverage/weight. Note the series of multiple hitch pin holes for that reason.
3) The mount is closer within the core of the AS frame to minimize loads on the far tail. It will be bolted to two internal frame spanners of the AS, such that torsion loads are mitigated.

Here's a few pics of progress this morning.

36" undermount hitch receiver. I have the farthest end bracket tacked on at the moment. Also note the addition of a anti-wobble nut at the bottom right.


Here's a pic of the furthest rear cross frame member behind the bumper. This is where most of the load will be. It'll be reinforced by sistering two right angle extrusions on each side, you can see the one on the outside. What you can't see is the additional screws I've added between the shell and frame. These screws are behind the rub strip to secure against any potential separation.

[pteck]

Testing the initial fit-up.

[tabney0315]

Originally Posted by pteck

Testing the initial fit-up.



Attachment 320346

Nice! That’s a very similiar approach I was initial going to take. This is great, I’ll be going with this approach. Thanks for posting.

[tbashin]

Adding a little more tongue weight to equal the weight of the rack and bikes will offset that weight. It ain't rocket science. If you are worried about sway from something as minimal as this then you need a bigger truck. That photo of the flipped Airstream had an SUV type car pulling it. That right there is proof enough for me that you need more truck and less weight distribution/sway devices to TRY to improve towing safety.

[pteck]

Originally Posted by tbashin

Adding a little more tongue weight to equal the weight of the rack and bikes will offset that weight. It ain't rocket science. If you are worried about sway from something as minimal as this then you need a bigger truck. That photo of the flipped Airstream had an SUV type car pulling it. That right there is proof enough for me that you need more truck and less weight distribution/sway devices to TRY to improve towing safety.

To your point, I am mounting an EU2200i to the tongue of my Airstream. That 50lbs there should easily restore any potential change in COG to the trailer. Additionally, there's ample of opportunity for me to loadout my airstream with more bags/weight in the forward bedroom of my 27FB.

I don't necessarily agree with a bigger truck to compensate if one's tow vehicle meets the capacity requirements . A trailer should be inherently stable within itself by having the correct percentage of tongue weight. While a large truck is nice for more payload and capacity if one needs it, using a larger truck as compensation for a badly setup trailer is buying false confidence. It can and will sway just the same.

[OTRA15]

Originally Posted by jhumphreys

. . .
Justin Humphreys here again.
. . .
COO- Airstream, Inc.

Thank you, Justin, for participating in that other thread. Any chance you could have Airstream reply in this thread about the company's feelings on folks adding rear-mounted hitches, bike racks, and storage boxes?

I had always assumed that AS's approval of the Fiamma bike rack, as the only approved one, also meant that nothing else heavier should be mounted further aft.

This debate has gone on for years, and a clear statement from Airstream would settle the issue, as well as promote safety for Airstream owners, their families, and the motoring public.

Thanks,

Peter

PS -- CC to AirstreamInc -- thanks.

Originally Posted by AirstreamInc

. . .
We look forward to helping you get this resolved.
. . .

[tabney0315]

Originally Posted by OTRA15

Thank you, Justin, for participating in that other thread. Any chance you could have Airstream reply in this thread about the company's feelings on folks adding rear-mounted hitches, bike racks, and storage boxes?

I had always assumed that AS's approval of the Fiamma bike rack, as the only approved one, also meant that nothing else heavier should be mounted further aft.

This debate has gone on for years, and a clear statement from Airstream would settle the issue, as well as promote safety for Airstream owners, their families, and the motoring public.

Thanks,

Peter

PS -- CC to AirstreamInc -- thanks.

If his comments are related to an un-modified trailer it may be helpful.

However, if the AS has been restored each will be different and his comments would not apply to all.

For example, the OP and I have added a significant amount of additional strength to the frame or other have rebuilt their frames to be stronger.

Additionally, how the weight is distributed throughout the trailer would impact it.

To make a general statement one way or the other that applies to all is just ineffective and inaccurate.

[perryg114]

Structural problems with Airstreams are caused when the attach points between the frame and shell break down. There are a few bolts and thin aluminum sheet metal holding these things together and that is at the front and back. The shell holds up the frame and if you put too much weight on the frame, it pulls loose from the shell. Also adding weight to the rear has a negative impact on stability. See this link.

https://www.youtube.com/watch?v=i2fkOVHAC8Q

Perry

[OTRA15]

Originally Posted by tabney0315

If his comments are related to an un-modified trailer it may be helpful.
. . .

That was implicit in the question IMO.

[pteck]

Originally Posted by perryg114

Structural problems with Airstreams are caused when the attach points between the frame and shell break down. There are a few bolts and thin aluminum sheet metal holding these things together and that is at the front and back. The shell holds up the frame and if you put too much weight on the frame, it pulls loose from the shell. Also adding weight to the rear has a negative impact on stability. See this link.

Perry

Love that video. It's incredibly useful to see and is eye opening for the uninitiated. Especially people new to towing that don't properly load out the trailer and avoid tongue weight.

If you'll note in the demonstration, they take the red weight off the nose of the trailer. The takeaway is not necessarily "don't remove weight from the front of the trailer."

Inasmuch as the takeaway is not necessarily "adding weight to the rear [having] a negative impact on stability".

The big picture here is that proper weight distribution is key to maintaining trailer stability. Even if only loading gear within the confines of the shell. It should always be considered. To your point, moreso when adding a rack onto the rear of the trailer.

[pteck]

Lots more progress today. Most of the job is complete, including fabrication, fitup, and welding. Here's what it looks like.


On the trailer frame, all structural additions are bolted on. The additions are 2x steel angle extrusions that run the full width, sandwiching the C-channel cross member, and ends at the main frame rails. One on the forward side of the rear cross member (can't see). One on the rear side (the one you can see) just above the hitch. I could have welded which requires more access, but I preferred the bolt through approach.

The angle brackets create structural ledges that the receiver can bolt to from beneath:

There's 4 main load bearing bolts closest to the receiver end for stability. The hitch extends to the next cross member which will bear minimal weight, but will account for the torsion loads. A weight distributing hitch if you will.

Undermount receiver:

This is the component that brings it all together, that requires some fabrication equipment and skill. Fully welded up here and ready to go.

If one wanted to reproduce it, some metal from home depot, angle grinder, drill, and tape measure is all it takes. Then bring it all to a welding shop. I'm just a casual DIYer, that loves modding cars, and learns by doing. My day job doesn't let me have hands on kind of fun. But I do engineer things quite a bit more complicated than this. If anyone is looking for a specific pic before I button things up, let me know.

[pteck]

Link to 36" receiver tube if anyone is interested in reproducing. Other metal components can be found at home depot.

https://www.amazon.com/Curt-Manufact...ds=36%22+hitch