GPSDyno
GPSDyno
GPSDyno · power measurement from GPS telemetry

GPSDyno

A run breakdown from a GPS file: laps, pulls, speed and a track map — plus the car's real power without a dyno.

SAE J1349 methodBHP · at the flywheeltrack matchinghow it works →
6GPS formats
1

Car

what we measure
Have a garage? — your cars with mass and aerodynamics will show up here.
2

Run

changes from run to run
You need a recording with a real GPS update rate above 8 Hz: Dragy, RaceBox, AiM, VBOX, an external receiver. A phone's built-in GPS records at 1 Hz — such a file won't compute.
How to export the file
RaceChrono · .rcz — session screen → “Share” at the top → RaceChrono (.rcz). On Android 11+ save it to Downloads or Drive: the browser can't see files in the app's folder
Dragy · .dlap — export the run from the app (dragy·Lap can also export .vbo)
AiM RaceStudio · .xrk / .xrz — the RaceStudio session file
VBOX · .vbo — the file from the logger's memory card
NMEA · .nmea — log of an external GPS receiver (Qstarz etc.)
not set
kg
With driver, fuel and gear — as the car ran. A mass error ≈ the same error in BHP.
Tiresnot chosen
digits only: 2254517
wheel ≈—auto
Left:

How it works

  1. 1
    Record a GPS run

    RaceChrono, Dragy, AiM RaceStudio, Harry's LapTimer, FastIron and other apps export .nmea, .rcz, .dlap or .xrk files.

  2. 2
    Describe your car

    AI can fill in the mass, Cd and frontal area, while tires and their size refine rolling resistance.

  3. 3
    Get the analysis

    Laps, pulls, speed and a track map, the power curve and the SAE J1349 engine BHP rating.

FAQ

A quick overview of GPS run analysis: what telemetry and what power GPSDyno computes, and what data quality depends on.

What exactly does GPSDyno compute?

GPSDyno breaks down a run from GPS telemetry: laps and lap times, acceleration performance (100→200 splits), top speed and a track map — and estimates real engine power (BHP). The power calculation uses speed, acceleration, mass, aerodynamics, tires, surface, elevation and weather.

Can you measure power without a dyno?

In our case, yes: GPSDyno can replace a chassis dyno for comparing cars against each other and for before/after runs. Different dynos often give noticeably different figures due to calibration, methodology and conditions, while here every run goes through a single model with GPS quality control and wind, mass and slope corrections. As a result, the scatter between comparable runs is usually smaller and easier to understand.

Is GPSDyno more accurate than a dyno?

It is more correct to talk about repeatability of comparison rather than the absolute accuracy of each dyno. GPSDyno provides a transparent estimate using a single consistent method with SAE J1349 correction, so a series of runs in one database compares more fairly than mixed results from different dynos.

Why does a single method give less scatter?

Because it removes a major source of differences: different dynos, calibrations, procedures and measurement conditions. In GPSDyno run conditions may vary, but GPS processing, filtering, the resistance model, wind corrections and quality scoring stay the same.

Which files can be used for the calculation?

Supported formats are .nmea, .rcz, .dlap, .xrk, .xrz and .vbo. Such files are usually exported by RaceChrono, Dragy, AiM RaceStudio, Racelogic VBOX, Harry's LapTimer, FastIron and similar GPS/lap-timer apps.

Why specify tires, tire size and surface?

Tires, wheel size and surface type affect rolling resistance and wheel inertia. The more accurate these parameters, the more stable the BHP estimate from run to run.

What affects result quality the most?

GPS log quality, recording rate, correct car mass, tire size and type, surface, wind and pull consistency. If the data is weak, the service shows warnings and rejects bad GPS points before the calculation.