Ultra Split Predictor

Forward pace model with sigmoid fatigue

Ultra Split Predictor

Plan your race and aid station timings.

What it does

Upload a GPX file from your race. The tool calculates predicted split times for each aid station using a fatigue model — your pace and climbing rate slow down over the race following a sigmoid curve. Adjust the parameters to match your fitness and race plan.

Adding aid stations interactively

After uploading a GPX, the Elevation Profile panel appears above the split table. Click + Add Aid Station to enter placement mode — the cursor becomes a crosshair over the chart and a hover marker shows exactly where you are on the elevation curve.

Click anywhere on the chart to snap to the nearest track point. A name form appears — type a short name (e.g. "Ridgeline") and hit Add or press Enter. The tool automatically assigns the correct aid station number based on position. Use Add Another to stay in placement mode for the next station.

Existing aid stations from your GPX are shown as orange dashed lines. New stations are renumbered automatically if you insert one between existing ones.

Export updated GPX

Once you have added aid stations, a GPX Export section appears in the sidebar. Set a filename (pre-filled with the original route name) and click Save GPX — the button highlights orange when there are unsaved changes. The exported GPX contains the full track and all waypoints in the correct Aid Station N - Name format, ready to reload into this tool or any GPX app.

Alternative ways to add aid stations

Your GPX can also come preloaded with aid stations marked as waypoints (not track points) with names in this exact format:

Aid Station 1 - Checkpoint Name
Aid Station 2 - Another Name
Aid Station 3

The number must be sequential. The name after the dash can be anything (or nothing). The tool auto-detects Start and Finish from the track.

How to add waypoints

Strava — build a route, click a point on the map, hit "Customize", set the name to the format above. Export as GPX.
Garmin Connect — open your course, add Course Points at aid station locations, set the name to the format above.
GPX.Studio — open gpx.studio, load your GPX, use the waypoint tool to add points along the route, name them as above, export GPX.
CalTopo / Gaia GPS — add markers on the route, export as GPX.
Any GPX editor — add <wpt> elements with <name> tags matching the format.

Parameters

Pace (fresh / fatigued)Your flat running pace at the start vs. deep in the race when tired. VAM (fresh / fatigued)Vertical Ascent Metres per hour — how fast you climb at the start vs. late in the race. Fatigue midpointThe hour at which you're halfway between fresh and fatigued. Roughly 60-70% of your finish time. Fatigue steepnessHow abruptly the slowdown hits. Low = gradual fade, high = sharp wall. Descent rateHow fast you descend vertically per hour. Treated as constant. Downhill factorHow much descending costs you. 0 = free speed, 0.8 = quad-destroying rocky descent. SmudgeGlobal time multiplier. Add ~5-10% for aid station stops, heat, or night sections.

Range mode

Each parameter has a ± range toggle. Enable it to set a "slow" value in addition to the base value. The tool then shows a time window (best to worst case) for each split — useful for race day uncertainty.

Saving configs

Type a name in the config box and hit Save to store your current parameters in the browser. Load or delete saved configs from the dropdown. Use this to compare scenarios (e.g. "optimistic" vs "conservative") or save settings per race.

Export CSV

Exports the full split table as a CSV file — useful for pasting into a spreadsheet or printing a pacer card.

Contact

If something doesn't work or you need help, please open an issue at github.com/landoskape/ultra-planner.

Upload a GPX file to see your predictions

Aid stations must be waypoints named "Aid Station N - Name"

Ultra Split Predictor