Triathlon Projection
How PIRX projects your triathlon finish time — swim, bike, run, and transitions combined into one number, with a range that reflects each leg's data quality.
PIRX projects your full triathlon finish time by modeling each leg separately — swim, bike, run, plus transitions — and combining them into one number. Sprint, Olympic, Half-Ironman (70.3), and full Ironman distances are supported. Triathlon mode is currently rolling out and is enabled per account.
How each leg is projected
| Leg | What PIRX uses |
|---|---|
| Swim | Your critical swim speed (CSS) — the pace you can sustain — from your recorded swims, adjusted for open-water race conditions |
| Bike | Your FTP (functional threshold power). With a power meter, straight from your rides. Without one, PIRX infers FTP from your speed and heart rate using a physics model |
| Run | Your running projection at the race's run distance, slowed by a personal fatigue factor (see below) |
| Transitions | Typical T1/T2 times for the race distance |
You do not need a power meter. If you ride with GPS and heart rate, PIRX estimates your cycling power from flat-road physics and scales it by how hard your heart was working.
The brick fatigue factor
Running off the bike is slower than running fresh. PIRX starts with research-based defaults for how much slower — about 2 percent for a sprint, 4 percent for Olympic, 8 percent for a Half-Ironman, and 13 percent for a full Ironman.
Then it personalizes. When you do brick workouts (a bike ride followed by a run within 30 minutes), PIRX compares your brick-run pace to your fresh-run pace. After at least three brick sessions, your own ratio replaces the default — so if you handle the bike-to-run transition better than average, your projection reflects it.
Why the bike matters more in longer races
Each leg's influence on your projected finish is weighted by how much of the race it represents. The bike share grows with distance:
| Race | Swim | Bike | Run |
|---|---|---|---|
| Sprint | 30% | 40% | 30% |
| Olympic | 25% | 40% | 35% |
| Half-Ironman (70.3) | 15% | 45% | 40% |
| Ironman | 10% | 55% | 35% |
This is why improving your FTP moves an Ironman projection more than improving your swim.
Cross-sport training credit
Training in one sport helps the others, and PIRX accounts for it. Cycling builds aerobic fitness that transfers strongly to running; running transfers somewhat less to cycling; swimming transfers modestly to both land sports. Your combined training load across all three sports also feeds a single multi-sport load ratio, so PIRX can see when your total volume is spiking — even if no single sport looks risky on its own.
The projected range
The range around your triathlon projection reflects each leg's data quality separately. Plenty of recent rides but few swims? The swim leg contributes more uncertainty, and the combined range shows it. As you log more consistent training in all three sports, the range tightens.
Related pages
Race-Anchored Projection
When PIRX shows a "Race-anchored" badge, your Projected Time is pinned to a real race you ran. Here is what that means and how the accuracy safeguards work.
Cross-Training in Your Projection
PIRX counts all your training — cycling, swimming, strength, elliptical, and more — toward your running projection, weighted by how much each type transfers.