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Old 12-18-2014, 02:08 PM   #43
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1981 31' Excella II
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Good luck on the long term reliability of that rig.

Perry

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Originally Posted by JamuJoe View Post
Nice job by the OP on a receiver mount. So much misunderstanding and misinformation on this topic, without clarity from Airstream. Monocoque vs semi-monocoque is a significant difference. Old chassis design vs newer models. No mystique to the overpriced Fiamma rack - it is clearly supported by the C beams and stabilized by attachment (with sheet metal screws) to the body. Airstream is simply negligent in not providing a receiver mount with clearly stated load capacity.

This Engineer took a different approach, extending the C beams by 12" with a "swim platform" on which I can carry a bike or other light cargo. Moving the bumper back 12" added crash protection to the rear end. 100 lbs on the tail decreased the tongue weight on my 2011 FC23FB from 14% to 13%. No noticeable change in towing characteristics in over 10,000 miles and all sorts of roads. Attachment 228814. No, the grandkids don't ride back there😉




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Old 12-18-2014, 02:46 PM   #44
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2011 23' Flying Cloud
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Taking the bikes along

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This explanation of how the Fiamma rack works makes perfect sense. Basically, it maintains the integrity of the body/frame connection by placing the same amount of stress on the body AND frame simultaneously.

Sorry, not correct. The braces attached to the shell will provide only a limited amount of lateral restraint. Look at the attachment of the braces at the rack frame. It rotates vertically on a little pin so as to not carry any vertical load. Not a bad design, but certainly dosen't reinforce body to chassis.


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Old 12-18-2014, 03:21 PM   #45
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Originally Posted by JamuJoe View Post
Sorry, not correct. The braces attached to the shell will provide only a limited amount of lateral restraint. Look at the attachment of the braces at the rack frame. It rotates vertically on a little pin so as to not carry any vertical load. Not a bad design, but certainly dosen't reinforce body to chassis.


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Yeah- that's exactly the conclusion I have come to in the last 24 hours....

Not sure I see the concept of providing torsional rigidity to the main frame rails either... There's definitely zero possibility of my frame rails twisting. The upper supports look to me, as an attachment point to just provide some stability to the upper part of the rack.... and not anything to do with a specifically engineered product to unify the shell and frame. Especially with #10 sheet metal screws in the the skin (even if 2 of them are into a rib)

Still watching for more comments and future conclusions
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Old 12-18-2014, 03:52 PM   #46
gpt
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maybe some of our engineer posters can clarify this question:

with the AS bike rack, the bikes are carried quite high. with my Yakima rack, lower but about 8-10" further to the rear.

which assembly is likely to create a greater 'moment of force', higher or lower?
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Old 12-18-2014, 04:05 PM   #47
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maybe some of our engineer posters can clarify this question:

with the AS bike rack, the bikes are carried quite high. with my Yakima rack, lower but about 8-10" further to the rear.

which assembly is likely to create a greater 'moment of force', higher or lower?
Higher or lower makes no difference, but farther to the rear would increase the force applied to the frame when the trailer hits bumps, assuming the same weight load.
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Old 12-18-2014, 04:20 PM   #48
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Higher or lower makes no difference, but farther to the rear would increase the force applied to the frame when the trailer hits bumps, assuming the same weight load.
thanks Steve.
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Old 12-18-2014, 05:01 PM   #49
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Having the CoG of the load higher does matter when you are considering longitudinal accelerations (braking, accelerating).

Having the CoG of the load further rearward matters when you are considering vertical accelerations (bouncing over bumps).

For both cases, having the load further away (in any direction) from the mounting point but without a brace allows relative motion in normal operation, and potentially introduces the issue of fatigue, even with small amplitude motion. Given that the older reports of separation refer to it happening over time (as I recall), I would look to reduce the relative movement of the two parts (trailer body and frame rails), and not just consider static loads on one or the other.

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Old 12-19-2014, 08:02 AM   #50
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Whatever you put back there you don't want it moving around because this creates a hammering affect that amplifies the load. A bike on the back of the trailer is probably not going to cause a lot of problems. Two or three bouncing around back there might. I would not put anything I care about on the back of a trailer. I either put my bikes in the trailer leaning up against the couch or in the tow vehicle with the front wheels off. I have also put them in a large roof trunk mounted on the tow vehicle. Water in the rain will saturate every part of that bike when mounted on the back. The chances of it getting stolen or damaged in a rear end collision are there as well. You can buy suit cases to store bikes in and even take them on airplanes. You do have to be able to take them apart and put them back together again. I see rear car carriers as a short trip transportation method not full time like when traveling. I am not going to put a $2000 mountain bike outside in the weather.

Perry
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Old 12-19-2014, 08:13 AM   #51
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Originally Posted by jcl View Post
Having the CoG of the load higher does matter when you are considering longitudinal accelerations (braking, accelerating).

Having the CoG of the load further rearward matters when you are considering vertical accelerations (bouncing over bumps).

For both cases, having the load further away (in any direction) from the mounting point but without a brace allows relative motion in normal operation, and potentially introduces the issue of fatigue, even with small amplitude motion. Given that the older reports of separation refer to it happening over time (as I recall), I would look to reduce the relative movement of the two parts (trailer body and frame rails), and not just consider static loads on one or the other.

Jeff
The longitudinal loads from braking and accelerating are insignificant compared to the vertical loads from the rear of the trailer bouncing over bumps in the road.

There's no way you can accelerate or decelerate at a rate great enough to stress the frame/body attachments, unless you had a head-on collision, and in that even the bike rack will be the least of your worries.
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Old 12-19-2014, 11:56 AM   #52
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The longitudinal loads from braking and accelerating are insignificant compared to the vertical loads from the rear of the trailer bouncing over bumps in the road.

There's no way you can accelerate or decelerate at a rate great enough to stress the frame/body attachments, unless you had a head-on collision, and in that even the bike rack will be the least of your worries.
For the bike rack, you are focusing on the loads from a single event, and not on the small loads that create recurring movement and potentially fatigue. Are we concerned with potential separation happening on the first trip, or after some time?

In a more general sense, if fore and aft loads aren't important relative to vertical loads (and I agree that they are less), why would the last three receivers I installed all include specific instructions from the vehicle manufacturer with limits for the maximum ball extension (rearward from the pin) permitted, but also for the maximum rise and drop permitted? This is in relation to the strength of the mounting of the receiver to the vehicle structure. Both offsets produce a bending moment at the mounting of the receiver to the vehicle. But the rear offset only relates to vertical loads, and the rise/drop offset relates to horizontal loads. Are you suggesting that is that just a collision concern?

Jeff
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Old 12-19-2014, 12:08 PM   #53
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For the bike rack, you are focusing on the loads from a single event, and not on the small loads that create recurring movement and potentially fatigue. Are we concerned with potential separation happening on the first trip, or after some time?

In a more general sense, if fore and aft loads aren't important relative to vertical loads (and I agree that they are less), why would the last three receivers I installed all include specific instructions from the vehicle manufacturer with limits for the maximum ball extension (rearward from the pin) permitted, but also for the maximum rise and drop permitted? This is in relation to the strength of the mounting of the receiver to the vehicle structure. Both offsets produce a bending moment at the mounting of the receiver to the vehicle. But the rear offset only relates to vertical loads, and the rise/drop offset relates to horizontal loads. Are you suggesting that is that just a collision concern?

Jeff
No, it's not a collision only concern, and your instructions stated above confirm my statement that the "farther to the rear would increase the force applied to the frame when the trailer hits bumps".

The same thing applies to a hitch ball mount, the farther away from the receiver, the greater the force applied from the tongue weight to the receiver when the tow vehicle hits bumps, and in reference to the max drop/rise, the greater these distances increase the torsional load on the receiver from the TRAILER, which is many thousands of times over the weight of a bike rack with bikes, put on the receiver when the tow vehicle stops and accelerates. The rack with bikes may be 100-150lbs, where a trailer could easily be many thousands of pounds. Not even close to a similar comparison.
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Old 12-19-2014, 08:34 PM   #54
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We briefly considered a front mounted hitch rack for our bikes but decided that the exposure to the elements (e.g., rain, road grime & bugs) would not be good for the bikes so we opted for the enclosed storage in the truck bed. If you are just hauling some casual "beach cruisers" the front mount could work.
I like GPT's design, but we initially opted for AAB's use of the truck bed. After many years of beating my brain on the interior of the cab-high shell, we discontinued carrying our bikes in the truck bed and opted for an Eddie Bauer.

More to the point - may I might point out that for those with (as mentioned in earlier posts ... and including ourselves) $2,000 bikes, the back of the trailer is the last place that I would carry either of our bikes - and they are not carbon fiber! However, you are entitled to your position. I would suggest that the low pressure area at the rear of any vehicle or trailer is where all of the fine road grit gathers ... onto the bike's headset, rear cluster, chain ring, cables, etc. It is simply imprudent to put anything mechanical -that is lubricated with oil -into such a dusty environment ... (then think of the rain / water contamination as well) unless you clean the contaminants before use or tear down and re-lube frequently. A short blast to the exposed road crud at the rear of your AS is likely to cause your bikes to collect more contaminants than most folks would experience on their bikes in many ridden miles... or years of use..

However, had I not already sold our receiver bike mount, I would entertain the OP's possibility to carry an inexpensive knock around bike. YMMV
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Old 12-19-2014, 10:23 PM   #55
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We have a Yakima receiver rack that we use when not towing the trailer. The AS recommended rack is so solid and perfect for both our tandem and (when going to places with dirt trails) our two mountain bikes. I cannot imagine a better, safer arrangement. Dave
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