Singular's 2.5″ brake ducts are designed to fit all 1990-2005 Miatas with wheel sizes 14″ and up.
Note: There are some limitation to the hose size which you can run to the ducts:
2.5″ hose is compatible with the factory under trays, requiring little to no modifications . We recommend the 2.5″ brake ducts for those who want the most cooling ability with the least amount of modification. 2.5″ hose can clear 15×9″ wheels with the factory undertray intact and without the use of any spacers.
In most cases, 3” hose requires a non-factory or fabricated under tray to clear 9” wheels or larger. With the factory plastic undertray removed, 3″ hose will clear 15×9 and 15×10 with a 5mm spacer.
It's is recommended that users run the largest size brake ducts that they are able to accommodate on their car. Brake pad and rotor life is increased further with the larger diameter units, as well as a larger reduction in operating temperatures.
Installation Guide: http://www.singularmotorsports.com/write-ups/brake-duct-installation-guide/