Track Day Data Logging on the ND MX-5
Data logging is what turns a track day from “that felt fast” into “I’m braking 40 feet early into Turn 5.” On an ND MX-5 you have three practical routes: a phone running a lap-timing app, an OBD adapter feeding vehicle data into that app, or a dedicated logger like an AiM Solo. Each gives you a different slice of data at a different price.
This page covers what’s worth logging, where the data comes from, and how the ND’s own sensors compare to bolt-on gear.
What’s worth logging
Section titled “What’s worth logging”Three layers, roughly in order of value for a driver trying to get faster:
- GPS position and speed — gives you lap times, a track map, and a speed trace you can overlay lap-to-lap. This alone tells you where you’re slow. Any phone GPS chip does ~1 Hz; a dedicated 10 Hz GPS (phone with a good chip, or a standalone logger) is the threshold where corner-entry and apex detail becomes usable.
- Driver inputs — throttle position, brake, steering. This is where the real coaching lives: you can see you’re coasting between brake release and throttle, or trail-braking inconsistently. The ND exposes throttle and RPM cleanly over OBD; brake pressure and steering angle are harder to get without CAN access.
- Vehicle dynamics — longitudinal/lateral G, yaw rate, individual wheel speeds. Useful for diagnosing under/oversteer and traction loss, less essential for shaving the first few seconds.
Most drivers get 90% of the benefit from GPS speed traces plus throttle and brake. Don’t over-buy on day one.
Route 1: Phone + lap-timing app
Section titled “Route 1: Phone + lap-timing app”The cheapest real logger you own is your phone. A modern iPhone or Android with a 10 Hz GPS chip running a lap-timing app (RaceChrono Pro or Harry’s LapTimer being the two serious options) gives you lap times, predictive timing, and a GPS speed trace with zero hardware.
Mount it solidly. Phone GPS is good enough for lap timing but the internal accelerometer is useless bouncing around in a vent mount, so rigid mounting matters if you want the app’s G data to mean anything.
This is the right starting point for most people. Add vehicle data only once you’ve outgrown the speed trace.
Route 2: OBD adapter for vehicle data
Section titled “Route 2: OBD adapter for vehicle data”To layer RPM, throttle position, and coolant temp onto your GPS trace, you connect a Bluetooth or Wi-Fi OBD-II adapter and let RaceChrono pull PIDs over the diagnostic port.
The catch is rate. OBD-II is request-response: the app asks for a PID, the ECU answers, repeat. When you’re polling several PIDs at once, you realistically get 2-5 Hz per signal — fine for RPM and throttle on a road course, marginal for anything you want to correlate tightly with corner entry. The factory port was built for emissions diagnostics, not telemetry.
For the ND, the high-value OBD channels are RPM, throttle position, vehicle speed, and the temps (coolant, intake). Use a known-good adapter — a quality OBDLink-class device polls noticeably faster and drops fewer frames than a $12 generic ELM327 clone.
Route 3: Dedicated lap timers and loggers
Section titled “Route 3: Dedicated lap timers and loggers”When you want sub-second-consistent timing and higher-rate dynamics data, a purpose-built unit earns its price. The common picks:
| Device | What it does | Approx. price |
|---|---|---|
| AiM Solo 2 | 10/25 Hz internal GPS, lap timing, predictive; GPS only (no vehicle data) | ~$400 |
| AiM Solo 2 DL | Same, plus CAN/OBD vehicle data logging | ~$550 |
| Garmin Catalyst | GPS lap timing with on-track coaching feedback | ~$1000 |
| VBOX Sport / Touch | 10-20 Hz GPS, high accuracy, motorsport-grade | $800+ |
These read GPS from their own internal antenna (mounted with a clear sky view, not buried in the dash), which is the main reason their positioning beats a phone in a car. The DL/CAN versions can also tap vehicle data far faster than OBD polling allows. For a fuller breakdown of the trade-offs, see data loggers compared.
What the ND’s factory sensors can actually give you
Section titled “What the ND’s factory sensors can actually give you”The ND already carries a useful set of sensors on its CAN bus — the question is access. The hardware behind the dash and ABS module includes:
| Signal | Source | Rough rate |
|---|---|---|
| Individual wheel speed (FL, FR, RL, RR) | Factory ABS wheel-speed sensors | ~17 Hz |
| Yaw rate | Factory gyroscope (stability control) | ~7 Hz |
| Longitudinal acceleration | Factory accelerometer | ~7 Hz |
| Engine RPM | Powertrain CAN | ~7 Hz |
| Vehicle speed | Powertrain CAN | ~7 Hz |
| GPS position/speed/heading | Built-in CMU receiver | 10 Hz |
These are automotive-grade MEMS parts (the same class Bosch and Continental supply for stability control), calibrated at the factory and rigidly mounted to the chassis. Read directly off CAN, they arrive simultaneously with no request-response overhead, which is why CAN logging beats OBD polling on rate.
The limits are real, though:
- The CMU’s GPS antenna lives in the dashboard, not under open sky — fine for a track map and lap timing, short of motorsport-grade positioning.
- There’s no external antenna input without a hardware mod.
- Factory sensor accuracy is whatever the car’s own calibration delivers; for verified bench numbers on the accelerometer in particular, see g-force accuracy.
- Power loss (stall, disconnected battery) stops any logging immediately.
If you want to log straight off the factory sensors without bolting external gear to the car, ScreenTune’s upcoming telemetry capability captures the signals above through the CMU itself; it’s in development. For most owners today, the phone-plus-OBD path is the proven, no-waiting answer.
A workable file format
Section titled “A workable file format”However you log, you want data that survives a stall. JSONL (one timestamped JSON record per line) is a good logging format for exactly that reason: it’s append-only, so a power cut leaves you with a valid partial file rather than a corrupt one, and each line stands alone. Most loggers and apps export to CSV for spreadsheet analysis and GPX for mapping the GPS trace, which is what RaceChrono, Track Attack, and most analysis tools want as input.
Suggested setup by budget
Section titled “Suggested setup by budget”- $0 extra: phone + RaceChrono/Harry’s LapTimer, rigidly mounted. Speed trace and lap times.
- ~$60-100: add a quality OBD adapter for RPM, throttle, and temps overlaid on your laps.
- $400+: AiM Solo 2 (or DL for vehicle data) for consistent timing and a proper external GPS.
Start at the top of that list. The speed trace will find you more time than another sensor will until you’ve stopped leaving it on the table.