[Rich]

with all this talk of tread depth, tightly controlled to 2/32 of an inch, it occured to me that different batches of tires could have a different diameter.

I would think that the diameter needs to be matched, and the tread depth would only be a good indicator of the issue with a particular set of tires.

I can't imagine that all of a particular model of tires are controlled within 2/32 (1/16) of an inch. I can imagine that one batch could be off more than this, however I'm not in the tire industry so I don't know the specifications.

I could imagine that the tire inflation (air pressure) in each tire could affect the diameter more than this amount, but perhaps I'm wrong.

Good luck with your new tires!

We just purchased a Ford Escape. They are available without the AWD (Ford tries to call it 4WD, but IMHO it's an AWD system on this vehical). But we went with the so called "4WD" system. So far we're quite happy with it. Got it with the larger 2L Ecoboost engine and the factory tow package. If you pussyfoot it around, I've seen 30 MPG on the dash gauges, but that takes a very concerted effort to maintain that for any length of time. They rate it lower than this. As they say, your milage may vary! LOL