I saw where a spare donut for a 2003 to 2010 Miata has a solution. But what about a 2011?

Trick way to go is just buy another wheel and tire to match the 4 on the ground- then if you bend a wheel racing around Laguna Seca, you whip out the matching spare and viola! still have matching wheels!

The RX-8 has the same lug pattern as your Miata. You should be able to pick one of these up at the dealer, but personally would search ebay its probly way cheaper than the stealership. On a side not I believe the spare should fit in Miata trunk with no issues.

Heres a good link that should have some good info for for you: http://forum.miata.net/vb/showthread.php?t=229959