I have a 1994 Mustang GT convertible with 75k miles.

After a returning from a trip to the body shop in which a tire was
replaced, I realize that I have 2 different-sized rear tires.  (The
fronts are smaller then the rears, and the shop replaced the rear size
tire with a tire of the same size as the front.)

Does this present any potential problems?

I'm presuming it does, but I want to confirm here.  The body shop has
agreed to replace the poorly-sized tire some time next week; the same
shop says I should have no problems with differently-sized tires.  I'm
not so sure.  I had considered taking a 300+ mile road trip over the
weekend, but decided to hold off.  Also, the anti-lock-brake light is
now appearing intermitently on the dashboard sensor light where it had
not previously appeared.  Further, I'm wondering if tire sizes (in
general, regardless of my situation) affect speedometer reports.  Does
my car need adjustment (eletronics or otherwise) for different sized
tires and the speedometer?  These tires are relatively new, and the
previous set had same sized tires all the way around, and I'm
wondering if the tire shop adjusted speedometer settings when they put
the big tires on the back.

To recap, the specific questions:

* Do different-sized rear tires present problems?  For the tranny
differential, or anything else?  If so, how many miles can I
reasonably drive with the diff sized tires?  (I can provide the exact
sizes later if needed.)

* Could diff-sized tires be contributing to my anit-lock-brake light
on my dashboard sensor?

* Are speedometer adjustments required after changes in tire size (in
general, regardless of my current sitaution) for my car?

Thanks for any help,
-Matt
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