Capture everything
A driver's first upload is almost always missing channels they already own the hardware to record. This is the setup pass that fixes it — before the next event, not after.
The rule this whole page enforces: you cannot recover a channel that wasn't recorded, and you can always re-derive from a native file you kept.
What each tier actually buys you
Not a feature list — what each one lets us say about your lap.
| Tier | Channels | What becomes answerable |
|---|---|---|
| Phone GPS alone | ~1–10 Hz position, speed | Lap times. Rough corner speeds. Little else — at 1 Hz a corner is 2–3 points. |
| + External GNSS | position, speed, altitude, heading @ 25 Hz (RaceBox Mini) | Corner-by-corner speed traces, distance-aligned lap-vs-lap, theoretical best, elevation. This tier alone can produce a full analysis. |
| + IMU | real lateral / longitudinal g, lean angle | Measured grip instead of curvature-derived estimates. Braking and cornering load separated. Combined g. The single biggest step up. |
| + OBD link | throttle %, rpm, gear, coolant/oil temp, MAP | Driver inputs. Where you lift, how you get to power, downshift quality, whether the car is heat-limited. Turns “you're slow there” into “you're slow there because you lift here.” |
The jump from phone GPS to 25 Hz external GNSS is the one that makes analysis possible at all. The jump to IMU is the one that makes it precise.
RaceChrono + RaceBox — the step everyone misses
RaceChrono derives its real Lateral Acceleration (G) and Longitudinal Acceleration (G) channels from an IMU — either the phone's internal sensors or the RaceBox Mini / Mini S's built-in IMU. With no IMU source active, those columns still appear in an export and are simply empty. No error, no warning. You find out weeks later.
Before the session
- GPS source = the RaceBox, not Internal. The usual first thing people get right.
- Confirm an IMU source is active. RaceChrono also has an expert setting, “Record internal sensors,” for the phone's own accelerometer and gyroscope (flagged experimental). Either path gets you g-channels.
- Verify with thirty seconds of driving, not the settings screen. Record a short lap of the paddock, open the session, and look for a non-empty lateral-g trace. A settings toggle you believe is on and a channel that is actually populated are different claims — only one survives an export.
Exact menu wording drifts between RaceChrono versions and between iOS and Android — check the app in front of you rather than trusting a path written anywhere else. The verification step above is version-proof, which is why it's the one that matters.
Send the .rcz, never the CSV
A RaceChrono CSV is a lossy projection of a session — whichever channels the export happened to include, at whatever rate it wrote. The .rcz is the native session archive: everything recorded, re-exportable to any format later. It's a zip container.
- One session: open it, hit Share on the session overview screen, export as .rcz.
- Everything: Settings → Backup → Export — one .rcz can carry many track days.
A CSV answers today's question. A .rcz answers every future one — when we add a new analysis in six months, we can re-run it over every .rcz we hold and over none of the CSVs.
Other loggers: Harry's LapTimer — export the session/database rather than a CSV. AiM — the RS2/RS3 project export, not just the CSV slice. TrackAddict — the full session log. Anything else — send the biggest, most native thing the app will give you and let us figure it out. We'd rather receive a format we have to write a parser for than a CSV that already threw the data away.
Upload
upload@trackdays.ai — attachments, zips, and Dropbox links all work. Include the car and the track if the file doesn't say.
Paddock checklist
Short enough to actually run between sessions.
- RaceBox powered, paired, GPS source = RaceBox
- OBD adapter paired, if you have one
- Record a 30-second paddock lap and confirm the lateral-g trace is not empty
- Session named with the track
- After the day: Share → export .rcz → upload@trackdays.ai
Questions, or your logger isn't listed here? bill@wrbaldwin.com. More on how the data gets processed once it lands: About.