well even though i should :slap: you bro for not searching i'll give you a link anyway h: :fawk:
http://www.miata.net/garage/tirecalc.html
use the calc. to determine what tire size you need to keep it close to stock for odvious reasons. now for closing the gap w/o lowering well a larger sized sidewall would do the trick since in making the rim size larger you make the tire size smaller to keep the same ratio so making both the rim and tire larger would lose some of the gap w/o lowering the car