How TriPB turns your numbers into a finish
No black box. Here is exactly what each input does, how the three bands and the cutoff calls are produced, where the race data comes from, and — just as important — where the model stops and your judgement (and your race’s Athlete Guide) takes over.
| Input | Affects | Direction of effect |
|---|---|---|
| Swim pace / 100m | Swim split + swim-cutoff margin | Slower pace → longer swim, thinner swim-cutoff margin |
| Wetsuit / open water | Swim split | Wetsuit speeds you up; open water adds ~6% over pool pace |
| FTP + weight, or flat speed | Bike split + run penalty | Drives a physics power↔speed model; harder effort = faster bike but a bigger run fade |
| Bike climbing (m) | Bike split | Climbing time = potential energy ÷ your power, partly recovered downhill |
| Wind & temperature | Bike + run | Wind adds aero drag; heat slows the bike slightly and the run a lot |
| Recent 10K / half / marathon | Run split (fresh baseline) | Riegel-projected to the race run distance, weighted to the closest PR |
| Run durability (1–5) | Run penalty | More long runs & bricks → you hold pace off the bike |
| First-timer at the distance | Transitions + run | Adds transition time and a small extra run fade |
Everything is deterministic and monotonic: the same inputs always give the same answer, and improving an input never makes you slower.
A single predicted time hides the one decision that matters: how hard to ride. So TriPB runs the whole race three times under three pacing disciplines.
- Aggressive — higher bike intensity, leaner transitions, slightly bolder swim. Faster bike, but the run penalty grows.
- Realistic — balanced, sustainable effort — the most likely outcome on the day.
- Safe Finish — protect the legs and the cutoffs: ride within yourself so the run holds together.
Each band is a full re-computation, not the realistic number ±X%.
The idea the whole tool exists to surface: you never run a triathlon on fresh legs. Your run is a function of how you rode.
We start from a fresh, open run projected from your PRs, then add a penalty: ~14% for a 70.3 and ~20% for a 140.6 at a balanced effort. That penalty grows with bike intensity, heat, first-timer nerves, and low run durability — and shrinks if you ride conservatively.
This is why "ride to a fast bike split" so often produces a slow overall time — the bike is borrowing from the run at interest.
Leave a field blank and TriPB substitutes a typical first-timer value and tells you it did. The honest consequence is a wider band, not false precision. Add your swim pace, a power number or a recent run and the range tightens around you.
The result always flags exactly which fields were estimated.
Triathlon’s hard problem is not the maths — it is that routes, cutoffs and aid stations change year to year. So every cutoff on a race page carries a source, a last-verified date, the clock basis (gun vs your rolling start), and a link to the official Athlete Guide.
We label each number template (the generic mass-participation structure) or verified, and the tool always defers to your race’s Athlete Guide for your year.
The fueling plan starts from widely used endurance ranges and scales them to your race duration, body weight, heat and sweat rate: roughly 60–90 g of carbohydrate, 400–800 mg of sodium and a fluid target per hour. These are starting points to rehearse in training, not prescriptions.
TriPB is an independent tool built by endurance athletes and engineers, not affiliated with IRONMAN or World Triathlon. The model is grounded in standard cycling physics and published endurance-sport ranges; the race data is compiled from public athlete guides and course information. It is not medically reviewed.
If a cutoff, course figure or projection looks wrong for a race you know, tell us — point to the Athlete Guide and we will correct it. That feedback loop is the plan for keeping the data trustworthy.