If you've plugged a course into Best Bike Split, you've seen it: a single number, usually somewhere between 0.65 and 1.10, sitting next to your projected finish time. That's your Intensity Factor, and it's arguably the most important input in the whole pacing model. Get it right and you ride to your potential. Get it wrong and you either leave time on the table or blow up with 20 miles still to go.
The Definition
Intensity Factor (IF) is the ratio of your Normalized Power (NP) for a ride to your Functional Threshold Power (FTP):
IF = NP ÷ FTP
If your FTP is 250 watts and you hold a Normalized Power of 200 watts for a race, your IF is 0.80. In plain terms, IF tells you what fraction of your threshold effort you sustained. It strips out the noise of a variable, hilly, windy course (that's what Normalized Power is for) and boils your effort down to one clean number you can compare across completely different rides.
This matters because raw average power lies to you on rolling or drafting-legal courses. Two riders can average the same watts on the same course and have completely different physiological costs depending on how variable their power was. IF, built on top of NP, corrects for that.
Why Best Bike Split Cares So Much About IF
Best Bike Split works backward from IF, not forward from it. You (or the tool's defaults) set a target IF for the race, and the algorithm distributes power across every segment of the course, accounting for gradient, wind, position, and equipment, to hit that target as efficiently as possible. The output is a second-by-second power plan that should produce your fastest possible bike split at a sustainable cost.
That last part is the whole game, especially in triathlon. The IF that would be optimal for a stand-alone time trial is almost always too high if you still have to run afterward. Best Bike Split's defaults are tuned with exactly that trade-off in mind, which is why the "right" IF changes so much by distance.
Typical IF by Race Type and Duration
These are general targets, not hard rules. Your personal number depends on FTP accuracy, run/bike fitness balance, heat, course profile, and experience. Use this table as a starting point, then dial it in with your coach based on file history.
| Race type | Duration | Typical IF | Notes |
|---|---|---|---|
| Sprint triathlon bike | ~20–40 min | 0.85–0.92 | Short enough that you can push hard and still run reasonably well. |
| Olympic/standard distance tri bike | ~1–1.5 hr | 0.80–0.88 | Best Bike Split's default is around 0.83. |
| 70.3 / Half Ironman bike | ~2.5–3 hr | 0.75–0.87 | Default around 0.78; stronger runners often push toward the top of the range. |
| Ironman / full-distance tri bike | ~4.5–6+ hr | 0.67–0.75 | Default around 0.70. Going higher almost always costs more on the run than it gains on the bike. |
| Century ride / gran fondo | 5–7 hr | 0.65–0.75 | Sustainable all-day pace with no run to follow. |
| Long endurance ride (training) | 2–4 hr | 0.75–0.85 | Standard aerobic/endurance training zone. |
| Long road race | >2.5 hr | 0.85–0.95 | Tempo-to-threshold effort sustained over a long event. |
| Short road race, criterium, or circuit race | <2.5 hr | 0.95–1.05 | High steady-state demand with repeated hard efforts layered on top. |
| Long individual time trial | ~40 km, ~1 hr | 0.95–1.05 | Classic "just below threshold, whole effort" pacing. |
| Short time trial | ~15 km | 1.05–1.15 | Above threshold; anaerobic contribution becomes meaningful. |
| Prologue TT / track pursuit | very short | >1.15 | Very short, heavily anaerobic; IF loses some of its usual meaning here. |
A Few Practical Notes
Your FTP has to be accurate for any of this to mean anything. An IF target built on a stale or inflated FTP will send you out too hard or too easy no matter how good the pacing algorithm is. Retest regularly, especially heading into a key race block.
In triathlon, treat IF as a bike-run trade-off, not just a bike number. If you consistently blow up on the run despite hitting your planned bike IF, that's a signal to lower the target, not to run harder off the bike.
Heat, humidity, and course-specific fatigue (technical descents, altitude, rough roads) all push sustainable IF down, even if the watts look fine on paper. Best Bike Split's weather and course inputs help account for some of this, but experience and race history should still adjust the final number.
Finally, IF is a planning and pacing tool, not a race-day scoreboard. The best use of it is in the plan you build beforehand and the file you review afterward, comparing planned vs. executed IF to see where the race actually went off script.
Dave Schell / Kaizen Endurance
Dave Schell is the Founder and Head Coach of Kaizen Endurance coaching based out of Boulder, Colorado, where he works with off-road cyclists of all abilities. Dave is the former director of coach education at TrainingPeaks where he traveled the world teaching coaches how to better use training software with their athletes.
Read more about Dave Schell at Kaizen Endurance.
