One nice thing about Airstreaming, is that you always learn something, more often than you would think.
I have many answers to many questions, as I should after 43 years with Airstream, but I never had a "positive answer" about this question, until today.
In the early 70's the axle mounting plates on the curbside, were moved forward 1/16, 1/8 or 3/16 of an inch, from the road side mounting.
I just love the answer.
A not to be named engineer at Airstream, so dictated that change, because he felt that the trailers would track better because of the typical crowning of the roads.
So a word of caution to the owners of the early 70's Airstream trailers.
Please check the distance from the lower forward part of the axle mounting plate, to the backside center of the tongue jack. That dimension should be exactly the same to both sides.
If you measure a difference, it will be 1/16, 1/8 or 3/16 difference. That difference causes two problems.
1. Your tandem axle trailer will have unusual tire wear typically on the curb side.
2. Your trailer will tow "dog leg." As an example a 31 footer, with 3/16 inch difference will tow dog leg 9 inches,
from front to back.
Once you have established that there is a difference in measurements from one side to the other, you can move the axles on one side either forward or rearward, by opening up the square notch and making the 5/8 inch mounting bolt holes oval.
It is suggested that a rearward movement would be better than a forward movement.
I know this is disappointing to many owners, but at least we now have, after all these years, a positive answer as to why the tires on some models have goofy wear.
For those owners that are replacing axles on the early 70's trailers, we suggest you check the axle mounting plate location, prior to installing new axles, just to make sure, one way or another.