How the Race Card works.

What you enter

Four current numbers are enough to begin. They are your pace per 100 m from a recent CSS test, your functional threshold power in watts, your weight, and your recent threshold pace per kilometre or mile.

Everything else is optional. You can add race context, recent results and bike setup when you have them. Each extra detail makes the relevant part of your range more specific. Leave a field empty and the model uses a broad assumption instead, and it tells you which one.

You can also add a recent open-water result, equipment detail for aerodynamics and tyres, and your transition experience. If you want to see where you would finish, the optional comparison uses only the finish times from past editions of the same race.

What it simulates

The model runs 500 simulated race days. Each one samples the parts of the race that vary, then the results are combined into a range.

• Swim. Your CSS pace is converted to an open-water pace. Without recent open-water evidence, the conversion uses a broad assumption.
• Transitions. Time in T1 and T2 varies with your experience and with wet conditions.
• Bike. Speed comes from a force balance at your planned power. It accounts for gravity, rolling resistance, aerodynamic drag, drivetrain efficiency, air density and the wind, resolved against the direction of each part of the course.
• Run. Your threshold pace is adjusted for the drop in run performance after the swim and the bike.

Repeating the calculation hundreds of times is what produces a range. The middle of the range is the likely outcome. The edges show where good and bad days land.

The course

The model uses each race's published distances. Where an organiser publishes none, it falls back to the standard distance for that format.

Where the route is known, it is split into segments with their own distance, elevation, grade, heading and surface. Climbs, descents, technical sections and exposed stretches then affect the bike and run in the places where they actually fall.

Course evidence has three states. Verified means the current year's route has been checked. Partial means the organiser's course description and latest published route are in use, but the final route is not confirmed. If neither exists, the course counts as unverified and its confidence rating stays low.

The conditions

Weather scenarios vary temperature, dew point, wind, gusts, rain and water conditions together, not one at a time. A hot, windy day and a cool, calm day are both possible, and the range reflects both.

A race-day forecast is not useful far from the race. Until it is, the model draws on weather from past race dates, and each race page shows that baseline. Closer to the race, a current forecast replaces it and the range becomes more specific.

Confidence

Confidence is built from four inputs. Each is rated low, moderate or high, and the overall rating is their average.

Athlete evidence

Rated high when a recent race-like result supports your threshold numbers. Without one, your numbers are taken as given and the rating is low. A recent race-like 10K or half marathon is what supports it.

Bike setup

Without setup detail, aerodynamics use a broad age-group assumption, the largest of the broad assumptions. Your bike type narrows it. A measured CdA narrows it further. A measured CdA that a recent power-and-speed result supports earns the highest rating.

Course evidence

High for a verified route, moderate for a partial one and low when the course is not verified.

Race-week conditions

Low while the model relies on the historical baseline. Moderate once a current forecast is supplied.

Confidence starts low when the inputs are broad and rises as the evidence improves. A narrower range means better information. It is not a guarantee.

What the range leaves out

The range covers a plausible spread of race days for your numbers. It does not predict your placing, the exact weather on the day or the decisions you make in the moment. Anything the model does not know stays visible as uncertainty rather than false precision.

Use the card to practise the decisions that matter before race day gets noisy: where to hold back on the bike, how to start the run and what to do if conditions turn.