Lap Data Analyzer

Analyze GPS track day lap times, sector splits, and speed profiles from GPX files or RaceChrono / Harry's Laptimer CSV exports. Everything runs in your browser — no data is uploaded anywhere.

1. Load your data file

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Drop GPX or CSV file here
or click to browse  ·  GPX, RaceChrono CSV, Harry's Laptimer CSV

How it works

This tool processes your GPS data entirely inside your browser using pure JavaScript — no account, no upload, no server.

GPX parsing Reads <trkpt> elements with lat/lon and <time> timestamps. Computes speed from consecutive point distances and time deltas.
CSV support Detects RaceChrono (Time/Latitude/Longitude/Speed columns) and Harry's Laptimer (GPS Export format) automatically from header row.
Lap boundary detection Auto-detects the start/finish cluster as the dense coordinate group near the session start. Detects crossing via signed cross-product: when adjacent GPS points straddle the finish line, the interpolated crossing time is used for precision.
Sector & speed calculations Distance via Haversine formula (R=6371 km). Sectors are equal-distance markers along the reference lap. Speed profile plotted against cumulative track distance.

Example: a 2-minute lap split into 3 sectors — S1 0:38.4, S2 0:45.1, S3 0:36.5 — the delta table shows how many milliseconds you gained or lost per sector versus your fastest lap.

Frequently asked questions

What file formats are supported?
GPX files (standard GPS Exchange Format used by Garmin, Wahoo, and most devices) and CSV exports from RaceChrono and Harry's Laptimer. For RaceChrono, export via "Export session" → CSV. For Harry's Laptimer, use "GPS Export" from the session menu. The tool auto-detects the format from the file header — you don't need to specify it manually.
How accurate is the lap time detection?
Accuracy depends on your GPS sample rate. At 10 Hz (100ms between points), the tool interpolates the exact crossing time of the start/finish line using linear interpolation between the two GPS points that straddle the line, giving sub-100ms accuracy. At 1 Hz (standard GPX), expect ±0.5 s accuracy. Use a dedicated motorsport GPS logger (Racelogic VBOX, AiM Solo, or a phone app at 10+ Hz) for competition-grade lap times.
How does auto-detect find the start/finish line?
The algorithm looks at the first 2 minutes of the session and finds the median position of GPS points — which is typically the pit lane or start/finish straight where the session begins and ends. It then constructs a virtual finish line perpendicular to the direction of travel at that point. For best results, start recording before you cross the line and stop after you cross it on your final lap. If the auto-detect is off, use "Pin on map" to click the correct location.
What is the speed color scale on the racing line?
The racing line uses a blue → cyan → green → yellow → red gradient where blue = slowest speed in the session and red = fastest. This lets you instantly see braking zones (color cools toward blue), apex speed, and acceleration exits (warming toward green/yellow/red). The scale is normalized per session, not a fixed km/h value.
Can I compare multiple laps on the speed chart?
Yes. After analysis, each lap appears as a toggle button above the speed chart. Enable up to all laps simultaneously to overlay their speed-vs-distance profiles. This is the most useful view for finding where time is gained or lost — look for divergence between your best lap line and another lap at the same distance marker to identify braking points and corner entry speeds that differ.