RE: [A/S] Hitch Height

["Oliver Filippi" <ofilippi@xxxxxxxxxxxx>]

Tom,

You raise a very interesting question. I never checked the revs per mile or
diameter of the current radial tire used by Airstream versus that of the old
700 R 15.  Like most of us, I assumed they were pretty close in the loaded
radius dimension.

It would also be interesting to know if Airstream has done anything to the
suspension in recent years that might affect the hitch ball height.  If they
are using the same axles, the newer trailers are a lot heavier and will sit
slightly lower.

That said, I think a little digression on this topic might be in order.
Please note that I am not trying to make things more complicated than
necessary or "B S" the issue.

The "Holy 19.5" hitch height" is the NOMINAL VALUE recommended by Airstream.
Like every other engineering measurement, there is a practical tolerance
which should be part of the spec.

Since there is no way to adjust the ride height of the trailer on its
suspension, there has to be some leeway.  For example, the same trailer
empty, versus fully loaded will ride at a different height.  Does this mean
you should adjust the ball height every time you fill the main fresh water
holding tank? or empty the waste tank? Of course not! (But if you listen to
some of the other posts, you might get that impression.)

If you look at the geometry of the chassis angle to the ground caused by
varying the hitch height it isn't all that much if you are within an inch or
so of 19.5"  One inch on a sixteen foot (192 inch) radius (distance from the
axles to the hitch coupling on a 25' trailer - I just measured my 25'
Tradewind) is not going to cause a huge difference in the angle of the
chassis to the road.  [I just worked out the trigonometry, and it comes out
to 1/3 of a degree for an inch of height variation up or down from the
nominal 19.5" value!) For a longer trailer, the angle would be even less.
This would apply to a hitch ball height variation OR a ride height variation
given a fixed (19.5" ball height.

Bottom line, I don't think it is worth splitting hairs over the ball height.
On the other hand, I would get very upset if I hired a hitch mechanic to set
the ball height at 19.5" and he didn't get it pretty close.

I don't know if this is the answer you were expecting, but I learned
something in persuing this discussion.

Bottom line:  If the tow vehicle hitch ball height is around 19.5", relax
and enjoy your Airstream. Adjusting your hitch spring bars to evenly load
your tow vehicle is a lot more important.

Oliver Filippi