'91 e30 alignment-balance-tire wear questions

["Luxury" <molux@xxxxxxxxxxxxxxxx>]

RE:  '91 e30 (delivered 12/90)

I am running a completely stock car, with Bridgestone Potenza RE950 at 4
corners.  At 70k miles, put 4 new tires on and did the balance/alignment.  New
shocks at 60k.

I had noticeable vibration at speeds from about 40-65 mph, which I attributed
to a wheel weight falling off, tire wear, etc.  After 65 mph, I think the
vibration was still there, but the frequency was high enough as to seem
"smooth."  So I had another balance/alignment.  This didn't really solve the
problem, but as I live in NYC and don't drive that much, and on the highway
even less, I didn't really notice it until a few months later--too late to
complain about it to the shop.  At about 78k miles, I took it in to have the
front tires balanced, which the shop did, but again, that didn't solve the
problem.  A few days later, with more time to spend, the car was up on the
lift and my mechanic pointed out a bent right tie rod.  They also pointed out
that the rear tires were almost bald on the inner edges, with good tread on
the outer edges.  Front tires look good.

Changed both tie rods, got 2 new tires on the back, balance and alignment.
The car seems much better at all speeds.  I think the vibration came from the
bent tie rod, but am curious about the digesters' opinion on this.

My other question is about the wear on the rear tires, which my mechanic says
could only really happen if the trailing arms were screwed up.  He says that
that is likely only if the car was in a serious accident that placed enough
pressure on axis with the rear axel (which has never happened).  The only real
unknown here is if at 73k miles, the alignment shop (next door to my mechanic,
where he sends all of his alignment work) rotated the tires.  What do you
think about this?

I want to keep the car in good shape forever, and drive modestly.
Unfortunately, there are potholes in NYC about 10 per block it seems, but
while I can easily see a relationship between front end damage from road
conditions, it is less clear regarding the relationship for the rear.  I don't
want to put >$1000 into new trailing arms, nor do I wish to replace the tires
every 10k miles.

TIA for any opinions.

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