Pace the course, not just the watts
Upload-free for now: pick a curated bike course and your power, and the planner returns a pacing plan that optimises total race time — the bike is the setup for the marathon, so it's bounded by an intensity (IF) target, a surge (VI) cap, a W′-balance durability ceiling, and a fuelling budget rather than chasing the fastest split.
Rider mass and FTP are shared with your athlete profile; swim/run pace come from there too (edit in the header). Total system mass 84 kg.
How this works & how to read the numbers click to expand
Everything is computed live in your browser — there's no server. Each time you move a slider the planner re-solves the whole course, which is why you'll see a brief Calculating… flash. The model is steady-state physics; it's a planning estimate, not a guarantee.
The objective: total race time
In a triathlon the bike isn't the race — it's the setup for the marathon. So the planner minimises swim + bike + run, not the bike split. Riding the bike harder shaves bike minutes but adds far more to the run; the plan finds the balance.
The physics
For every 50 m of the course it balances your power against air drag (CdA), rolling resistance (Crr), gravity (grade) and drivetrain loss to get a speed, then sums the time. Anaerobic fatigue is modelled via W′ (see the power numbers); wind and heat aren't yet (see roadmap).
The power numbers
- Avg — plain average power.
- NP (Normalized Power) — weights hard surges more; closer to the physiological cost.
- IF = NP ÷ FTP — intensity. Ironman sits around 0.68–0.78 (green).
- VI = NP ÷ Avg — how surgey the ride is. Capped near 1.05 so you don't shred the run.
- W′ — your anaerobic tank (kJ) above Critical Power (≈95% FTP). Surges drain it; easy riding refills it. The W′ reserve stat is the lowest it gets — empty it and the planner caps the surges you can't afford, and the run pays for it.
Gradient sections
The course is split at the feet and crests of its hills — each climb or descent is its own section, and the rolling stretches in between stay whole. Each row shows the speed, average watts and a cue (push the climbs, ease the descents). Hover a row to find it on the map.
Variable vs constant power
The comparison shows what smart pacing buys: at the same average power, spending watts where they're cheapest (climbs) and easing where they're not (descents) beats holding one steady number the whole way.
Fuelling & the run
Carbohydrate burn is estimated from the work done and intensity, against your hourly intake — a deficit warns you'll fade. The run estimate penalises over-biking and under-fuelling, which is how a faster bike split can still mean a slower race.