GTrace - G-Meter & Logger

Track day or mountain road, every G you used stays on record.

GTrace turns your iPhone into a real G-meter. It draws the lateral and longitudinal G-forces from your cornering, braking and throttle as a live trace, then lets you replay the run against the map, your footage or the graphs.

One-time purchase. No subscription, no in-app purchases.

WHILE YOU DRIVE

• Live G-G diagram, lateral and longitudinal G shown together
• Trailing trace, with peak lateral and longitudinal G held on screen
• Jerk shown as a crosshair, so you can see how smoothly you transfer load
• Speed readout, switchable between km/h and mph
• Audible alert when you exceed your chosen G threshold
• Comfort and Sport modes with separate display ranges for street and track
• Three display layouts: standard, info + speed, and video preview
• Phone holder mode, so a vertically mounted phone still reads longitudinal G correctly

MEASUREMENT

• Gravity component removed to isolate true vehicle acceleration
• 2nd-order Butterworth IIR low-pass filter with adjustable cutoff frequency
• Configurable sampling rate
• Axis inversion, so mounting orientation doesn't matter

AFTER THE RUN

• G-G heat map showing which part of the friction circle you actually used, so you can see the balance between cornering, braking and acceleration at a glance
• Synced playback: G-G + map, G-G + video, G-G + acceleration graph, or map + graph, at adjustable playback speed
• Time-series graphs for longitudinal G, lateral G, longitudinal jerk, lateral jerk and speed
• GPS trace drawn on a map, with top and average speed

RECORD AND SHARE

• Voice recording, synced to the acceleration data for commentary and notes
• Video recording with audio, played back with the G-G trace overlaid
• CSV export for spreadsheets or your own analysis tools
• Native binary format (.ggx) import and export, for backups and moving data between devices

WHO IT'S FOR

• Track day, sports driving and time attack enthusiasts
• Drivers working on their technique on mountain roads
• Anyone chasing smoother, more passenger-friendly load transfer
• Motorsport competitors who want their practice data kept
• Anyone who wants their car's behaviour in numbers

English and Japanese. iPhone only, iOS 15.6 or later.

Note: measurements use the iPhone's built-in accelerometer and gyroscope. Mount the phone firmly in the vehicle for accurate readings. Note: GPS trace and speed recording require location permission. Note: this app does not include lap timing.