Scott - in thinking about your tire scalloping situation - here's something to ponder:
When your (single axle) trailer was new - it was available in both single axle
and twin axle formats.
As you've mentioned - 26' for a single axle is a lot of length for a travel trailer
to begin with. Add to that how the factory tuned it and how the owner loads it and
maintains it and tows it and you've got even more to take into consideration.
In looking at RJ's photos from '55 thru '60 - it looks to me that depending on what
year the Overlander was offered (single axle version) there may have been year to year
differences in the actual location of the axle when looking at the frame/shell. Some
years appear to have the single axle placed in the very center of the shell (fore and
aft) and some years appear to have the axle mounted rear-of-center when looking at the
shell of the trailer from the side.
If so - these changes very likely may have had to do with (among others) the year-to-year
weight changes in kitchen/bath locations etc.
Depending on how these single axle models have been remodeled and updated over the years
- (weight shifted) - this could have serious balance implications on the original factory
design for the frame/shell/axle.
I'm pretty sure your family one-owner Overlander is probably still in it's original layout
etc - but if you've made any weight distribution changes (permanent trailer components) -
you might consider this as one reason for "odd" tire scalloping. I say "odd" - if after all
the new service work you're doing is completed and all the "usual suspect" issues have been
confirmed as being "not suspect".
The single most interesting class I took years ago in Auto Mechanics school (Spokane Community
College) was the "drivetrain and driveline" vibration class.
The single most important thing I learned is that just because there is a vibration/wear issue
present in a vehicle - you never should assume the vibration/wear issue is being caused by
something obvious.
Sometimes the source(s) of vibration/wear issues end up being no where near the point of actual
wear.
The place that shows wear is often a weak link in a design - and not the actual part that is
vibrating or otherwise overworking itself.
A weak link might be an unintended structural (drooping frame and shell etc) feature - or in the
case of a tire (I would suggest tires are an intended wear feature) (within reason) - it wears out
faster than most other components on a trailer. Being a natural indicator of reasonable wear to
begin with - tires can also be wear-and-tear absorber(s) above and beyond the reasonable wear and
tear they absorb while revolving and contacting pavement.
I now find it fascinating to look underneath a vehicle and note where vibration dampening weights
and absorption devices have been mounted. Often a manufacturer will counteract the
vibration/imbalance rather than design it out! In otherwords - they install counterweights and/or
dampening devices to deal with issues.
Often times you'll see odd add-on devices to the tailhousing of a transmission. One of the better
known vibration dampeners was the four-door Lincoln Continental convertible from the early 1960's.
If you look under the four fender corners of one of these convertibles - you'll find very basic and
very large counterweights mounted on spring arms. On the one hand the design of the Lincoln was new
and dramatic for the time (low to the ground) and on the other hand that new design featured "issues"
that subsequently showed up...that had to be dealt with one way or another...and in the case of the
inherently more sensitive chassis design of a convertible model...that meant gym weights under the
fenders!
It might be worth comparing the axle location on your 1960 Overlander with other single axle
Overlander owners and then comparing tire wear stories.
Also - you might want to think about your tire wear issue in terms of what was normal for tire wear
when the trailer was new (not now). In otherwords - there weren't any radial trailer tires available
- and owners may have been changing their bias-ply tires more often. If not for good measure (like
today) - then maybe just because they were wearing out faster.
Maybe your trailer axle design is simply meant for "more often tire replacement"....due to the individual
reality of how your specific trailer bounces, wiggles, shimmies etc...etc...etc. regardless of how many
ways one balances everything out. Modern tires are no doubt generally better than what was available
in 1960 but...they may not be better for your specific trailer. The modern tires are possibly intended
to match up with modern chassis designs - while your old chassis may simply be overworking them...no
matter how well they are made.
Good luck and travel safe. RL