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Hitch heights are typically listed in the Airstream owner's
manual for the subject trailer.
In my case, the height to the TOP of the ball (2 5/16"
diameter) is listed at 19 1/2" [1976 Tradewind}. I think this is the
height for most of the recent models since the early 70's.
The manual does say that this height is with the tow vehicle
loaded which would also include the load of the trailer tongue on the tow
vehicle.
I recently switched tow vehicles and had my Reese weight
equalizing ball mount removed and re-welded to the draw bar by an experienced
local welder who does a lot of trailer hitches.
He mounted the ball mount an additional 3/4" higher than the
19 1/2" to allow for the settling of the tow vehicle under the load of the
trailer tongue. Note that the weight equalizing spring bars are going to
distribute the tongue weight to both the front and rear wheels of the tow
vehicle, so that the tow vehicle retains its fore and aft angle to the road
(typically parallel or thereabouts). In my case the tow vehicle was a 3/4
ton pickup. A lighter duty truck (say a half ton pickup) would probably
have slightly weaker springs and would probably drop a tad more under
load. In this latter case, the top of the ball might be set an inch higher
than the loaded height on an unloaded vehicle.
If you can find an experienced shop, they know exactly what to
do, given the specified ball height, the tow vehicle, and the tongue weight (and
gross weight) of the trailer.
If you are really concerned, you might want to get two
hitches, first the adjustable one, and also a welded one. This way, you
could, via trial and error, set the adjustable hitch to the proper height on a
level surface with the trailer and tow vehicle fully loaded, and spring bars
properly adjusted. Then the welder could position and weld the ball mount
to the draw bar in exactly the same position as the one on the adjustable
assembly.
Although the bolt together adjustable hitch is OK, I am not a
fan of bolts for this application. I have much more confidence in a
properly welded ball mount/draw bar - no chance of the bolts getting loose under
traveling vibrations.
Oliver Filippi
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