Short answer is to the question of whether or not Airstream underestimates their tongue weight ... I'll state up front that this assertion is mostly "false".
Note: I posted some of this in another thread yesterday that was mostly devoted to a different topic. Subsequently, I figured this deserves it's own dedicated thread.
Now to begin the topic at hand ...
Since joining the airforums back in Feb, I have read literally hundreds of postings reminding newbies that you can expect tongue weights way above the factory spec when you receive your new trailer.
This isn't really true, I found out. This knowledge came as a serendipitous discovery when I decided to weigh my "factory fresh" 2022 Globetrotter 27 FB Twin on the way home from the dealer.
Experimental conditions (yeah, I'm an engineer, so sue me
):
The Cayenne S was empty except for the driver and passenger up front and a full tank of fuel.
The Airstream had full propane bottles and a couple of Interstate Flooded Lead Acid batteries up front, but was otherwise empty (except for whatever Airstream provided at the time of purchase). Note: We drained all of the Airstream tanks before we left the dealer lot.
CAT Scale results:
Pass number 1 on the CAT Scale (trailer hooked up, with tension on WD bars):
3060 lbs TV Front Axle Load
3260 lbs TV Rear Axle Load
5880 lbs TT Axles Load
Pass number 2 on the CAT scale (trailer hooked up, no tension on WD bars)
2460 lbs TV Front Axle Load
4080 lbs TV Rear Axle Load
5660 lbs TT Axles Load
Pass number 3 (tow vehicle only, full tank, 1 driver, 1 passenger up front)
2860 lbs TV Front Axle Load
2620 lbs TV Rear Axle Load
That's the end of the measurements. Now for the results of some spreadsheet calculations:
5480 lbs Tow Vehicle (TV) weight
12200 lbs Gross Combined Weight (weight of trailer and tow vehicle)
6720 lbs Travel Trailer (TT) Weight = Gross Combined Weight - TV Weight
1060 lbs Travel Trailer Tongue Weight***
*** Note: the TT tongue weight measurement includes hitch weight @ 95lbs + friction anti-sway (2*14.6lbs) + Tekonsha Brake Controller @ 5.5lbs)
Now, let's calculate the Tongue Load Transferred to TT Axles when WD is active:
220 lbs transferred to TV axles when WD System is Activated
840 lbs Tongue Load transferred to TV axles
5480 lbs TV weight
12200 lbs Gross Combined Weight
6720 lbs TT Weight = Gross Combined Weight - TV Weight
1060 Tongue Weight (includes hitch weight @ 95lbs + friction anti-sway (2*14.6lbs) + Tekonsha Brake Controller @ 5.5lbs)
Now, let's calculate the Tongue Load Transferred to TT Axles when WD is active:
220 lbs transferred to TV axles when WD System is Activated
840 lbs Tongue Load transferred to TV axles
So, that's the results of the CAT scale measurements and some simple calculations to derive some other values that are of critical importance.
So now, let's get to the main topic of this thread: Does Airstream publish optimistic values for their trailer tongue spec?
The gospel truth here on the forum is that Airstream spec's for tongue weight are grossly optimistic.
Let's dig into that a little bit.
As stated by Airstream:
Tongue weight as delivered from the factory should include the weight of two full tanks of propane and two flooded lead acid batteries.
For my trailer (2022 Globetrotter 27 FB Twin), the spec for tongue weight is 875lbs.
The measured tongue weight from the CAT scales yields a value of 1060 lbs.
So, Airstream is wrong? Not entirely true ...
The spec from airstream doesn't include the weight of anything "the customer will add to the tongue".
In my case, I added:
94.5lbs for the Eax-lift Elite 1000 WD hitch
29.2lbs for two Husky friction anti-sway bars (14.6 lbs each)
5.5lbs for the Tekonsha electronic brake controller
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129.2 lbs is what I added to the trailer tongue
So, 875 + 129.2 lbs = 1004.2lbs
Hmm, 1004.2lbs still doesn't add up to the 1060lbs that I measured. So, what am I missing?
What if Airstream doesn't really account for weight of the propane in the bottles and weighs the tongue with empty bottles?
The reason why I ask this question is that I managed to inspect my trailer right after Airstream delivered it to the dealer (i.e. before the dealer had a chance to do anything to the trailer) and I noticed that the propane tanks were empty at that time. However, when I took possession of the trailer, the dealer had filled both bottles of propane.
So, how much does the propane inside two 30lb propane bottles weigh? No, it's not a trick question ... the bottles cannot be completely filled with liquid. The built in OPD (Overfill Prevention Device) ensures that some space is left at the top of the tanks for propane vapor to form. Trust me, you don't ever want to have liquid propane make it's way into any downstream devices such as ovens, grills, heaters, etc unless you like to explode :-).
So, what is the total weight of propane in two 30lb propane bottles? The answer is 55lbs.
So, if I add up the following:
875lbs for Airstream factory spec for the tongue weight
94.5lbs for the Eax-lift Elite 1000 WD hitch
29.2lbs for two Husky friction anti-sway bars (14.6 lbs each)
5.5lbs for the Tekonsha electronic brake controller
55.0lbs for propane
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1059.2lbs is the grand total if you are estimating the eventual tongue weight before you take possession of your new trailer.
Now, let's refresh our memories as to what was my measured tongue weight for an "as delivered from the factory Airstream", but with two full tanks of propane instead of empty propane tanks? You already know the answer ... it was 1060lbs.
1059.2lbs is the estimated pre-delivery tongue weight and 1060lbs is the actual measure tongue weight as delivered from the factory. I would say these two values are pretty much equal
So, the Airstream factory spec for the tongue weight is actually, well ... mostly correct ... if you also add 55lbs to account for the propane that Airstream said was included in the trailer spec (but clearly was not in point of fact).
Conclusion: If you want to know the tongue weight for the trailer you want to buy, you will need to take the Airstream factory spec, add 55lbs for propane in two 30lb bottles (or add 77lbs for two 40lb propane tanks) along with adding whatever additional weight you will tack onto the tongue yourself for the WD hitch and any brake controllers, etc. This will be accurate within less than a pound or so of total rounding error.
Side note: yes, the "full" weight of the WD hitch is considered to be part of the tongue weight. Arguments that the stinger is actually attached to the tow vehicle and should be accounted for as part of the tow vehicle weight are really moot. So don't buy some god awfully heavy WD hitch and then try and complain about Airstream delivering trailers with tongue weights way above spec
I hope this helps any prospective future Airstream buyers and I hope this helps clear up the incorrect "common knowledge that Airstream tongue weight specs are grossly underestimating the actual tongue weight".