Data Loggers Compared

Every lap timer answers the same first question, how fast was that lap. They diverge sharply on the second one: why. The gap between a device that flashes a lap time and a system that overlays throttle, brake, and steering against your fastest run is the gap between knowing you were slow and knowing where. Here’s how the four common setups compare on an ND Miata.

What actually determines accuracy

Lap timing precision comes down to GPS sample rate. A phone’s built-in receiver typically updates once per second (1 Hz). At 80 mph that’s a 117-foot gap between fixes, and the timer interpolates everything in between. Dedicated units sample far faster: the AiM Solo 2 DL uses a 25 Hz GPS, and external pucks like the RaceBox Mini run 10–25 Hz. More fixes per second means a tighter, more repeatable lap time and cleaner speed traces through corners.

In practice the gap is smaller than the spec sheet suggests. Apps like Harry’s LapTimer and TrackAddict apply smoothing, and many drivers report 1 Hz phone times landing within a tenth or two of transponder timing. A 25 Hz receiver buys you consistency lap-to-lap and trustworthy mid-corner data, which matters more for analysis than for the headline number.

The second axis is car data. A pure GPS timer knows position and speed and nothing else. To see what your hands and feet were doing (throttle, brake, steering, RPM, gear), the logger has to read the car’s bus. On the ND that’s where the OBD-II port comes in.

The four setups

AiM Solo 2 DL

The DL (“data logger”) version of the Solo 2 is the standalone enthusiast benchmark. It pairs a 25 Hz GPS with a 100 Hz six-axis inertial platform (roll, pitch, yaw) and, via the included OBD-II harness, pulls ECU channels like RPM and throttle onto the display and into the log. Track maps are auto-detected; you analyze afterward in AiM’s free Race Studio software. It’s the most expensive option here (well north of the DIY phone rigs, typically a few hundred dollars more than a RaceChrono setup), and it’s a dedicated box you mount, wire, and live with. The payoff is reliability and a self-contained workflow that doesn’t depend on your phone surviving a hot cabin.

Garmin Catalyst

The Catalyst is the odd one out: it’s a coaching tool first, a logger second. It uses high-rate GPS plus its own sensors and a forward camera, and its signature trick is the “True Optimal Lap” — it splices your best individual sectors into one synthetic best-possible lap and gives real-time audio cues (brake here, more entry speed there) through earbuds or the stereo. What it deliberately does not do is read your ECU: no throttle position, no RPM, no brake-pressure trace. If you want a device that tells you in plain language where to find time without ever opening a laptop, it’s excellent. If you want to dig into the car’s behavior, it’s the wrong tool. Note there are two generations in the wild: the original Catalyst and the Catalyst 2 (announced early 2026, around $1,200). Check which one a used listing actually is.

RaceChrono Pro + OBD-II reader

This is the enthusiast sweet spot for an ND, and the most flexible. RaceChrono Pro (a one-time app purchase on iOS/Android) runs on your phone, takes GPS from an external receiver (RaceBox Mini, Qstarz, Garmin GLO, VBOX Sport), and reads the car over a Bluetooth OBD-II adapter. The widely recommended adapter is the OBDLink MX+ run in RaceChrono’s experimental CAN mode, which reads the ND’s CAN bus directly rather than polling standard OBD-II PIDs — that lifts the effective sample rate to roughly 40 updates/second and unlocks channels regular OBD-II won’t give you.

The ND community has done the reverse-engineering legwork here. The open-source RaceChronoDiyBleDevice project documents the ND’s CAN IDs and conversion equations, including brake pressure and steering angle, which aren’t exposed as normal PIDs. The work was tested on a 2019 ND2 RF and applies broadly across ND years. With those channels mapped you get throttle, brake, steering, RPM, and speed overlaid on the GPS trace for a fraction of a Solo 2 DL’s cost (a capable rig lands around $250–300 plus the app). The tradeoff is fiddle: you’re managing a phone, an adapter, a GPS, and a channel config rather than a single sealed box.

Phone-only apps

TrackAddict (free tier available) and Harry’s LapTimer run on the phone alone, using the internal 1 Hz GPS and the phone’s accelerometers. Cost is essentially zero and setup is a windshield mount. Accuracy is good enough to find seconds when you’re starting out, and TrackAddict can read an OBD-II adapter too if you add one later. The ceiling is the 1 Hz GPS and the lack of car data — fine for “am I getting faster,” thin for serious corner-by-corner analysis. It’s the right place to start before spending money.

Quick comparison

Setup	GPS rate	Reads car data	Coaching	Rough cost
Phone app (TrackAddict / Harry’s)	~1 Hz (internal)	Optional via OBD adapter	No	Free–low
RaceChrono Pro + OBDLink MX+ + GPS puck	10–25 Hz	Yes (CAN: throttle, brake, steering, RPM)	No	~$250–300
AiM Solo 2 DL	25 Hz	Yes (ECU via OBD-II)	No	High
Garmin Catalyst / Catalyst 2	High-rate GPS	No	Yes (real-time audio + optimal lap)	~$1,000–1,200

How to choose

Just want to know if you’re improving: start with a phone app. Don’t spend until you’ve outgrown it.
Want to analyze your driving and the car on a budget: RaceChrono Pro with an OBDLink MX+ and a GPS puck. The ND’s CAN data is already documented, so you get pro-grade channels cheaply.
Want a sealed, reliable box and don’t mind the price: AiM Solo 2 DL.
Want a coach, not a spreadsheet: Garmin Catalyst. Just accept it won’t tell you what your right foot was doing.

The reason this matters beyond the lap time: the most useful data is the data you actually look at, and that means it has to be easy to capture and easy to read together. A GPS trace tells you that you lost time in turn 5; a throttle-and-brake trace tells you that you lifted early and got back on the gas late. Integrated logging (GPS, car bus, and video in one synced view) is what turns a number into a fix. That’s the case for capturing it all in one place rather than stitching three apps together after the session, and it’s the direction the forthcoming ScreenTune track edition is built around.