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 into stretches of consistent gradient — flat, gentle climb, descent, etc. 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.