GPS lap timer, telemetry analyzer, and optimal-lap coach for autocross, HPDE, track days, and time trials. Most lap timers tell you what your time was. GridLine tells you where the time went.

Import a session from RaceChrono, AIM, VBOX, TrackAddict, Apex Pro, or any CSV — or record live using just your phone's GPS — and GridLine builds a physics-constrained model of your fastest theoretical lap from your own driving. It then overlays that ideal line on a satellite map of the actual venue and shows you, foot by foot, where you're leaving time on the course.

After three runs (autocross) or three laps (track day), the lap analysis is real. You'll see the corner you under-rotated, the brake zone where you trailed too long, the straight where you lifted early. Every zone gets a time-loss number. Every session gets a coaching tip ranked by where the most time is hiding.

For autocross drivers
- Built for parking-lot courses, where the start and finish lines move every weekend and the official timing trap is the only number that matters.
- Refine your start and finish lines from your official run times — paste your score-sheet times and GridLine back-solves the line positions until the computed times match the officials. Your phone's GPS gets timing-trap accuracy, retroactively, so every delta in the rest of the analysis is anchored in reality.
- Drop start and finish lines anywhere on the satellite map — no pre-built track config required.
- Combine multiple recordings of the same event into a single session.
- Sessions save even before you've placed a course — capture first, configure later.

For track day, HPDE, and time trial drivers
- Per-zone time-loss breakdown. The course is auto-segmented into 8 to 18 zones by curvature and lateral G, and every zone gets a delta showing exactly how much time you lost there versus your theoretical optimal. Coaching tips are ranked by where the most time is hiding.
- Sector best splits across the laps in a session, plus an optimal sector-best lap that stitches together your best sector from every lap.
- Pick any lap from any session as a reference and ghost-overlay it on the satellite map. The faster line shows up directly on top of the slower one.
- Speed-delta map overlay shows you, foot by foot, where you're carrying more speed than your reference and where you're giving it back.

What you get
- Satellite-map overlays: speed, time loss, grip utilization, consistency, lap-vs-lap
- Optimal-lap calculation that's car-independent and bounded by what you've actually demonstrated — never assumes faster than you've driven
- Sector best splits and per-sector optimals
- Bravery score (grip commitment, independent of lap time) and on-limit percentage
- Trail-brake score, dead time, min-speed average, grip envelope
- Live GPS recording — no external data logger or hardware required

Works with your existing data logger
GridLine reads telemetry from RaceChrono (.rcz), AIM Solo / Solo 2, VBOX, TrackAddict, Apex Pro, and any CSV with GPS and speed. Bring the lap data you already have — no need to switch lap timers.

Privacy and pricing
GridLine runs entirely on your device. Your telemetry and lap analysis never leave your phone. Free to use, no subscriptions, no ads, no account required.