So Im having the darnest time looking for a spare tire for the GSX. The GSX uses a 16" spare. The tire size is T125/70D/16.

My noob question is, would any spare with the same tire size work or do donuts have offsets too? Also, the Miata tire size calculator doesnt go as small as 125. How much smaller is this diameter than my 225/40/18 wheels?