Autocross / SCCA Classing for the ND Miata

The ND MX-5 is one of the most common cars at any SCCA Solo (autocross) event in the country. It’s light, balanced, cheap to run on a set of tires, and it sits at the front of one of the most competitive classes in the rulebook. The question almost everyone asks first is “what class am I in?” — and the answer depends entirely on what you’ve bolted to the car.

SCCA Solo classing works on one principle worth burning into memory: the rulebook is a list of allowances, not restrictions. If the rules for your class don’t explicitly say you may do something, you may not do it. There is no “well, it doesn’t say I can’t.” A single non-compliant part drops you to the next category up, where you’ll be racing cars with far more prep.

The categories, from mild to wild

SCCA Solo stacks its categories roughly by how much modification is permitted. From least to most:

Street — near-showroom. The popular ND home is here.
Street Touring — bolt-on suspension, intake, exhaust, wheels.
Street Prepared — coilovers, suspension geometry changes, more.
Street Modified / Prepared / Modified — increasingly unlimited, increasingly expensive.

Each category is split into letter classes by performance potential (A, B, C, etc.). The ND lands in a different letter in each category, so the full name matters: “CS” and “AST” are two different worlds.

C Street (CS) — the stock-ish home

A bone-stock or lightly-modified ND lives in C Street, abbreviated CS. This is where most ND owners start and where the class is deepest and most cutthroat — national-level CS times are separated by hundredths.

Street category is the most restrictive. The allowances that matter for an ND:

Tires: any DOT-legal tire with a UTQG treadwear rating of 200 or higher. No true R-comps or slicks. In practice the class runs the stickiest 200-treadwear tires available (the “200TW” race tires).
One sway bar. You may change, add, or remove one anti-roll bar — front or rear, not both. The stock ND already has both, so the usual move is a stiffer rear bar and leave the front alone.
Dampers (shocks). You may fit aftermarket shocks, including adjustables. Koni and Bilstein units are common choices.
Springs must stay at the OEM rate. You cannot change spring rates in Street category. This is the single biggest reason the trim you buy matters (see below).
Alignment within the car’s adjustment range, and the usual bushing/end-link/exhaust-after-the-cat type allowances.

Why the Club trim wins in CS

Because you can’t touch spring rates in CS, you want the car that left the factory with the rates you’d want anyway. The Club trim is the pick: it ships with the limited-slip differential and a stiffer rear spring (roughly 100 lb/in versus about 80 lb/in on lower trims). The LSD and the extra rear rate are exactly what you’d add if the rules let you — so buy them from Mazda instead. Sport and Grand Touring cars are at a baked-in disadvantage in CS that no legal mod can erase.

ND2 cars (2019+, the 181-hp Skyactiv-G 2.0 with the higher 7,500-rpm redline) have a power edge over ND1 (155 hp) in the same class, which is worth knowing if you’re shopping specifically to compete.

Street Touring — read the letter, it changed

Street Touring is the next step up: it opens the door to spring/coilover changes within limits, intake, exhaust, and a wider wheel-and-tire allowance, still on a 200-treadwear tire.

Here’s the trap. SCCA reorganized and renamed the Street Touring category for the 2025 Solo rules. The old letter classes (STR, STX, STH, and so on) were replaced with names that mirror the Street and Prepared categories — AST, BST, CST, DST, EST, GST. In that shuffle, the ND Miata moved from the old STR into A Street Touring (AST). Most of the legacy STR field went to CST instead, so older forum threads telling you “the ND runs STR” are now wrong on the name even when the spirit is right. If you’re looking at any classing advice written before 2025, confirm it against the current rulebook.

The prepared classes — CSP and beyond

Add coilovers with non-stock spring rates, do real suspension geometry work, or run a setup outside the Street/Street Touring allowances, and you’re into C Street Prepared (CSP) and above. The ND is a strong CSP platform: stiffer, lighter, and able to fit more tire than the cars it shares the class with. But cost is the gatekeeper. Past CSP sit Street Modified, X Prepared, and the fully-built classes, which are populated by purpose-built cars and budgets to match.

The honest progression: most people run CS for years, because the car is already class-competitive and a fresh set of tires is the only consumable that matters.

How to actually find your class

Make a complete list of every non-stock part on the car — including the wheels and tires.
Open the current-year SCCA Solo Rules (Appendix A lists the car’s base class; the category sections list what each class allows).
Start in the lowest category and check every mod against its allowances. The first category whose rules permit all of your mods is your class. One unlisted part and you move up.

SCCA also publishes a “Class My Car” tool, and most regions are happy to sort a new competitor on site at their first event. When in doubt, ask before you run — running out of class is the most common rookie mistake, and it’s avoidable.

Logging your runs

Autocross runs are short, typically 30 to 60 seconds, but they’re where a data logger earns its keep, because the only way to find the half-second you left in a sweeper is to overlay two runs. A GPS-based lap timer or data logger that captures speed and lateral g lets you compare line and braking points run to run. See track day data logging for how on-car logging fits an ND.

Autocross tires for the ND — what 200-treadwear actually means on this car
Alignment specs and settings
Sway bar options — picking the one bar CS lets you change
Suspension and coilovers — once you’ve decided to leave Street category
Lap timing apps and data loggers compared
Community and forums for region-specific classing help