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Which IRONMAN courses are fastest? How the course speed score works
When you are choosing a race, how fast the course is usually comes down to what other people tell you. Some say Kona is hard. Some say Penghu is flat. Both are only half right. Kona's terrain is not actually that hard; what makes it hard is the wind and the heat. Penghu really is flat, but when the April monsoon is blowing, it rides like a climb.
The speed score turns those vague impressions into a number you can compare across courses.
How is the score calculated?
Every course starts at 100 and loses points in four categories, with a floor of 30:
| Factor | Deduction | Cap |
|---|---|---|
| Terrain | meters of elevation gain per kilometer × 1.8 | −30 |
| Technical (corners) | density of corners that force you to slow down × 0.13 | −12 |
| Heat | each degree of race-day temperature above 24°C × 1.2; each degree below 10°C × 0.5 | −14 |
| Wind | typical race-day wind speed (m/s) × 2.2 | −16 |
100 means ideal conditions for riding fast: flat, cool, no wind, few corners. 90 and above is a Very fast course, 80 to 89 Fast, 70 to 79 Neutral, 60 to 69 Hard, and below 60 Very hard.
The four caps differ on purpose. Terrain carries the most weight, because climbing really does cost extra energy and no position or equipment lets you dodge it. Technical, meaning the corners, has the lowest cap, because slowing for a corner costs a few seconds at a time, and corners alone rarely make a course hard.
What does each factor measure?
Terrain looks at meters of elevation gain per kilometer, not total elevation gain. 1,800 m over 180 km and 900 m over 90 km both average 10 m per km, so they lose the same points. That is what lets full-distance and 70.3 courses sit in the same table.
Technical is about corners, and only the ones that actually force you to slow down: the direction has to change by more than 25 degrees within one stretch of road, so the natural bends of a country road cost nothing. A U-turn is 180 degrees in one go, which is why multi-lap city courses with repeated U-turns lose more here.
This rule has been changed once, and Challenge Roth is the reason. An early version counted every natural bend on the German country roads, which cost Roth 15 points and flatly contradicted its reputation as a fast course. Once only the corners that force you to slow down were counted, Roth's Technical deduction dropped to 3.5.
Heat and Wind use the average of the actual weather for the same time of year over the last five years. The data is long-term reanalysis from meteorological agencies, so it does not depend on how many times the race has been held. Even a first-year race gets a complete score from day one, as long as its dates are known. Once you pick an exact race date in the dashboard, these two are recalculated from the forecast for that day.
One honest note about the heat deduction: at the same power, hotter air is less dense, so you actually ride slightly faster. The real cost of heat is to your body, because the power you can hold drops. That is why heat is left out of the finish-time calculation and only affects this score.
Seven example courses
One thing stands out in the chart: two courses that both sit around 70 can lose their points for completely different reasons. Taitung full distance gives up some to terrain and some to wind; Kenting loses almost all of it to wind. The same athlete racing both needs to train different things: one calls for power control on rolling terrain, the other for the position and the mindset to ride into a headwind.
What the score is not
It rates how easy a course is to ride fast, not how fast you will ride it. Your finish time comes from your power plan. The score answers one question only: given the same ability, on which course is a good result easier to come by?
It also has known limits. The weather comes from a single location, averaged over the hours of the bike leg, so it underestimates stretches with strong local wind. The crosswind on the road to Hawi at Kona is the classic example: it blows much harder than the score suggests. The plan is to move to sampling at several points and correct it with uploaded ride files, and this article will be updated when that is done.
The rankings themselves are here: global course rankings, filterable by region and month. The verification badge next to each score tells you where the route came from: an official route, ride-verified, or a public community route not yet rechecked.
Picking a course still comes down to your own strengths. The score tells you what a course demands; whether you have it, you already know.
Courses in this article
