Tires: Explorer tires, goodyear wrangler, explorer tires

Question
I have an Explorer Sport with P255/70R16 tires.  I only have
25,000 miles on the vehicle but the tires have worn oddly and
cause vibration so now I need new ones. For strictly monetary
reasons I was wondering if I could switch to a 235/70R16 tire
since that size is bit cheaper. ( I am looking at getting Michelins
which are pricey, but I do want a good tire.)    Also my spare tire
(Goodyear Wrangler) has never been used.  At 5+ years old,
would it be okay to keep it as a spare or should it be replaced as
well?

Thanks for your time.  

Answer
Karen,

If your vehicle came a certain size, it's best to stay with that size.  In your case, going smaller is a bad idea.  Overloaded tire failures can sometimes have tragic results.

What you need to do is get your vehicle aligned and rotated the tires frequently.  While this will not absolutely prevent this wear pattern (Some of this is in the vehicle.), it will maximize your tires life.  Also monthly inflation checks will help greatly (also improves your safety!)  If you don't do this, then it doesn't matter how expensive the tires are, because you haven't addressed the cause of the tire wear.

The latest thinking is that tires have a finite age limit, even if they are unused.  Some folks say 6 years, some say 10 year, but it appears to be dependent on the outside temperature.  So if you live somewhere where it is hot, go with the lower value.