>If I move to 16 inch rims, would it be best to put 215/40/16 *** on
>them? The faq on miata.net says 205/45/16 are the best fit but the
>215 size seems to be almost an exact match for the stock tire in
>diameter when I use the tire calculator...
stock (or whatever insanely small tolerance you choose) is kind
of silly. Why? Because tires will wear ~3/4" in diameter over
their life (~3+% change). Plus, with tire pressure (which the Miata
will demand much lower than the sidewall rating), effective diameter
is also different from what the calculator would state.
Meaning: if someone's tried both sizes, and they have a
reasonable explanation (ride, fit, fender clearance, etc.)
for why one size is better, I'd say that opinion is more
significant than a small delta on the size calculator.
IME, 205/50/15's can hit the fender, so 215's on heavier 16"
rims will be quite likely to hit the fender. That's probably
the basis for choosing 205 over 215.