Free GPS dyno — web-based, nothing to buy
Horsepower from GPS telemetry.
Upload a lap log from RaceBox, Dragy or RaceChrono. GPSDyno rebuilds your power curve from speed data — physics, not guesswork — and corrects the peak to SAE J1349, so runs from different days actually compare.
WORKS WITH: RaceBox · Dragy · RaceChrono · VBOX · any NMEA logger
How it works
A dyno day, minus the dyno
01
Record
Do two or three full-throttle pulls on a track or airfield. Any GPS lap timer from 5 Hz up works; 10–25 Hz is the sweet spot.
02
Upload
Drop the log file on InRace and enter your car's weight. Add aero figures for a tighter estimate — sensible defaults cover the rest.
03
Physics
GPSDyno reconstructs the force at the wheels from how speed actually changes — accounting for aero drag, rolling resistance and slope.
04
Read the curve
You get the full power curve, peak BHP corrected to SAE J1349, lap splits and a report you can share or save as PDF.
What you get
More than one number
Curve
Full power curve
Not a single figure — the whole P(v) shape. Spot where boost falls off, where a map goes flat, what a tune really changed.
Compete
Track leaderboards
Your run lands on the leaderboard of the circuit where you recorded it, in a weight-to-power class against similar cars.
Browse circuit leaderboards →Events
Digital challenges
Time-boxed events: same track, same window, public standings. Bring a stock hatch or a built car — classes keep it fair.
See open challenges →History
Garage history
Every run is tied to your car. Before and after a remap, an intake, a wing — the curves tell the truth, side by side.
Start your history →FAQ
Fair questions
How accurate is a GPS dyno?
With a 10–25 Hz logger, still air and a reasonably flat straight, back-to-back runs land within a few percent of each other — repeatability is the method's strength, and it's exactly what you need to verify a tune. Absolute accuracy depends on the weight you enter and on conditions, so treat results as a consistent estimate, not a certified dyno sheet.
Do I need to buy hardware?
No. GPSDyno reads files from gear track drivers already have: a RaceBox or Dragy box, RaceChrono on a phone with an external GPS, a VBOX, or any logger that writes NMEA. A bare phone's 1 Hz GPS isn't enough for power math — 5 Hz is the minimum.
Which files can I upload?
RaceChrono .rcz, Dragy .dlap, VBOX .vbo, AiM .xrk / .xrz, and plain NMEA — up to 50 MB per file.
What does it cost?
Nothing. A free account on inrace.net, unlimited runs, leaderboards and PDF reports included.
Why GPS instead of a rolling road?
A dyno session costs money, books out weeks ahead and clamps your car to someone else's correction factors. GPS pulls are free, repeatable at the same place on the same day, and SAE J1349 normalization makes them comparable across weather. For before/after work it's the more honest instrument.
Your car has a number. Find it.
FREE · NO HARDWARE TO BUY · RESULT IN ABOUT A MINUTE