one of the rear tires in my old car has a very slow leak from a brad
in the tread, that I haven't fixed, since it is mainly driven in a
city, but it has been down to 7psi after I drove it on the highway,
and it still is intact. Being oversized and on the rear of a FWD car,
it has to get really low before it looks low. Since I never had a tire
fail or uneven wear in my 50 yrs of driving, I guess I do something
right. Those oversized tires have some pretty big cracks in the
sidewall on the inboard sidewalls. Good thing I only see them when I
have the tires off. )) To me the outer rubber is mainly to protect the
fabric from abrasion, which it isn't going to get very easily on the
inner sidewall. I worry more about the smaller, recommended size front
tires for the car, because of the extra weight they have to carry. The
rears can probably carry double the weight they do.

As long as you're within reasonable limits on the tire manufacturer's
spec, go with whatever's comfortable and provides the level of
responsiveness that your driving style demands.  Vehicle
manufacturer's specs are often bogus.  For example, I used to drive a
Suzuki Samurai, a vehicle with an ultra-short wheelbase, a pair of
solid axles and a rock hard truck suspension with zero compliance.  To
appeal to the US market, Suzuki recommended 24 psi (may be off on the
nymber but sure it was low-mid 20's) to soften the ride. Of course,
the handling was awful.  Consumer Reports aside (everyone remembers
the rollover "test" with the ouriggers that appeared on 60 Minutes,
but nobody seems to know that after a prolonged legal battle, CU was
forced to admit that they "never intended to imply that the Samurai
easily rolls over in routine driving conditions."  With 35 psi, it
handled well and was very responsive.  Not a Lotus, mind you, but out-
cornered any other SUV (actually transformed a pure "utility vehicle"
into a "sport utility vehicle".  The ride was "somewhat" rough, to say
the least.  Only time I used the factory spec was when driving in
sand, where it was unstoppable, just as it was in snow, mud, gravel,
etc.  Okay, a little wordy, but just wanted to say that manufacturers
may specify less than optimum numbers for reasons that have nothing to
do with performance.  By the way, that Samurai lasted 20 years,
130,000 miles and spent the last two years of its life as a tractor
hauling rocks and stumps through the woods clearing a hiking/biking
trail through my brother's mountain retreat.  Never had a serious
problem with it; survived a rear-end collision with a dump truck that
lost its brakes, drove it from Nags Head to Lake Placid and on the
beach at Chappaquidick (no great fan of Ted Kennedy, but that bridge
he drove off would be trouble for a sober driver in broad daylight).
Best "cheap" new "car" I ever bought.