The Bormio approach to the Stelvio Pass: roughly 21.5 km of climbing topping out at 2758 m, the second-highest paved pass in the Alps. Averages 7.1% with some sustained 9–10% pitches, fewer hairpins than the iconic Prato side but still a serious altitude effort. Often used in the Giro d'Italia as the Cima Coppi.
Yes. You get course-specific pacing from a GPX file using the same core physics model that paid planners like Best Bike Split rely on. This tool is free, runs in your browser, and has no account requirement. Paid services add features like live weather forecasting and Garmin or Wahoo race-day integration. If you want accurate time and power predictions for a specific course without paying a subscription, this covers it.
The physics model captures the four main forces acting on a rider: aerodynamic drag, rolling resistance, gravity, and drivetrain friction. Validated against four of my own Strava rides ranging from 1h to 4h, the constant-power physics prediction was 2-8% optimistic versus actual moving time. Error grew with duration and climbing density. The calculator surfaces this directly as three estimates (optimistic, likely, worst case) so you can plan against a realistic time. The main residual sources of error are cornering on technical descents, traffic and micro-stops, and rider fatigue, none of which a physics-only model can see.
Optimistic is the pure physics result: what the model says if you ride at the configured power with no traffic, no cornering on descents, and no fatigue. Likely adds a real-world overhead that grows with duration (~2% baseline plus ~1.2% per predicted hour), based on validation against my own rides where the calculator was consistently 2-8% fast. Worst case adds a larger pad for technical descents, headwinds, or a bad day. Plan against likely; benchmark against optimistic.
Any standard GPX 1.0 or 1.1 file with track points and elevation data. Exports from Strava, Komoot, RideWithGPS, Garmin Connect, and Wahoo all work, as do files from course-builder sites like bikeroutetoaster and plotaroute.
Yes. Four bundled courses are ready to load in one click: Alpe d'Huez (15.6 km / +1153 m), Mont Ventoux from Bédoin (21.4 km / +1576 m), Stelvio Pass from Bormio, and the Kona Ironman bike course (181 km / +1620 m). Useful for trying the tool before you have your own route, or to see how you'd go on the ride of your dreams.
Yes. Switch to the Route Map tab to see your track overlaid on OpenStreetMap, with each segment colored by its gradient band (same Wahoo-style scheme used on the elevation profile). Hovering on either the map or the elevation profile highlights the same point on the other, so you can see exactly where on the road each gradient shows up. Includes a fullscreen toggle.
Yes. The race-intensity presets map to common durations: All-out (under 1h) for sprint triathlon or short time trial, Hard (1-2h) for Olympic distance, Steady (2-4h) for Half Ironman or gran fondo, and Endurance (4h+) for full Ironman or ultra-distance. Pick the preset closest to your target and fine-tune from there.
FTP (Functional Threshold Power) is the power you can sustain for about an hour. You can skip it and set climb and flat watts directly. Entering your FTP makes the intensity presets more useful by scaling power targets to the expected race duration.
CdA is your drag coefficient multiplied by frontal area, measured in m². It captures how aero you are. Rough reference values: tops ~0.38, hoods ~0.32, drops ~0.30, time-trial clip-on bars ~0.27, pro TT position with skinsuit and aero helmet ~0.20. The 'How does this work?' panel on the tool page has the full table.
Yes. Set a headwind or tailwind in km/h and it gets factored into the aerodynamic drag calculation. Live weather forecasting is not included yet, so check the forecast closer to race day and enter the expected wind manually.
IF (Intensity Factor) is your Normalized Power divided by your FTP. It tells you how hard the effort is relative to your threshold. TSS (Training Stress Score) combines intensity and duration into a single training-load number: a 1-hour ride at FTP scores 100 TSS. Both show up in the results when you enter your FTP.
Yes. The Race Plan button in the Course Breakdown section opens a summary of your pacing strategy. From there you can copy it as text (for pasting into forums or group chats), download it as a CSV (for spreadsheets), or print it (tape it to your stem).
Yes. For efforts longer than ~75 minutes the race plan includes a fueling calculator: total carbs needed for the ride, broken down into gels, bars, or drink-mix bottles, plus a "top up every X min" cadence so you can stick to the rate without thinking about it. The suggested carbs-per-hour scales with duration and intensity, following mainstream sports-nutrition guidance: shorter or easier rides need less, longer or harder rides approach 90 g/hr. You can override the rate manually.
No. The GPX parsing, physics, and your saved preferences all run in your browser. Nothing is uploaded to any server.