If you track a Miata, a proper roll bar is the first real safety mod, and Hard Dog is the community reference. Add a fixed-back seat and harness only as a matched system with the bar, never a harness without something to protect your head and neck.
A convertible offers little rollover protection, and most track organizations require a roll bar with adequate height and bracing. This is safety gear first, stiffness second.
- Roll bar: Hard Dog is the benchmark. Their bars (Sport, Hard Core, M-series) are proven and available in single- and double-diagonal, harness-bar configurations. Get the double diagonal if you want SCCA/NASA compliance and a harness mounting point, most people wish they'd bought it from the start.
- Broomstick rule and height: The bar must sit above a line from the seat to the top of the windshield to actually protect a helmeted head. Pick the taller/aggressive option if you'll wear a helmet.
- Fixed-back seat holds you in place so you can feel the car and use the belts properly. A good FIA-style seat plus proper mounts is a big upgrade in control and safety.
Harness caution, this matters:
- Never run a 5/6-point harness without a roll bar and preferably a HANS/head-and-neck device. In a frontal hit a harness holds your torso while your head keeps going, submarining and neck loading are real risks. The stock 3-point belt is safer in a car with no cage.
- Mount harnesses correctly to a harness bar at the right angle; bad mounting is worse than no harness.
Sane order: roll bar (double diagonal) first, then seat, then harness plus head-and-neck, as a complete package. Buy safety gear as a system, not one piece at a time, and buy it before you buy speed.