[brucepick]

I managed to get a tread depth gauge years ago. You could use a little ruler instead.

When I got my new tires I checked the tread depth. Slightly deeper in the center than at the outer areas. Been running them at 52-53 psi for about 14K miles now. 44 psi sidewall rating. Still slightly deeper in the center than the outer areas.

I've also heard:

1) They will last longer at higher pressure due to less rubber flexing and heat buildup
(I completely expect that to be true).
and
2) They don't need rotation because they will wear more slowly and cleanly (I'm not sure if I buy that one completely but there's probably LESS need for rotation at higher pressures).