Here is the truth that saves people money: an NA or NB Miata does not need big brakes. The car is light, and the factory discs are entirely adequate for street and most autocross use.
The reality by generation:
- NA 1.6 (1990-1993) has the smallest discs, roughly 9-plus-inch front and rear solid/vented setup. Fine for a 2,100-pound car.
- NA 1.8 (1994-1997) stepped up to larger rotors, about 10-inch front, sharing calipers with the 1.6 but with different brackets, pads, and rotors.
- NB and especially the Sport package (2001-2005) brought the largest factory Miata brakes, with bigger rotors and larger caliper pistons. These "Sport" brakes became standard on the last NBs.
What this means for you:
- Fade on a light car is usually fluid and pads, not caliper size. Before spending on a big brake kit, flush in fresh high-temp fluid and fit a better pad compound. That solves the vast majority of "my brakes fade" complaints.
- The 1.8/Sport brakes bolt onto earlier cars as a cheap, factory-parts upgrade if you genuinely want more. This is the sensible path before aftermarket kits.
- More rotor does not shorten stops on street tires. Your tires set the limit. Bigger brakes buy repeated-stop fade resistance, nothing more.
Decisive answer: for a street NA/NB, keep the factory-style brakes, run good fluid and pads, and put your money into tires. A big brake kit on a street Miata is jewelry.