Triathlon race predictor.
Physics-based bike model with race-specific elevation for Sprint, Olympic, 70.3 and Ironman. Predicts every split + total finish, W/kg, carbs and fluid.
How the bike prediction works
Most triathlon calculators divide distance by an average speed. This one solves for the speed at which your race-day power exactly balances three forces: air drag, rolling resistance and gravity on climbs. Race-day power is set from your FTP and the distance, around 95% of FTP for a Sprint and 82% for an Ironman.
Why elevation changes your split
When you pick a course, its total bike elevation gain is spread across the course as an average gradient. Climbing costs power in proportion to your total weight, so heavier riders lose more time on hilly courses like Lake Placid or Mont Tremblant than on flat ones like Florida or Eagleman. For the same reason, W/kg matters more than raw watts on hilly courses.
Bike type and position
On flat roads, air drag is the biggest force. The model assumes an aero time-trial position (CdA about 0.23 m², rolling resistance 0.0042). On a road bike with clip-on bars or a more upright position, your drag is higher, so expect a slower bike split than predicted, especially on fast, flat courses.
Off-the-bike running
The run split starts from your open run pace, adds a 4% off-the-bike fade, and adds time for the run course's elevation gain when you pick a race.
Frequently asked
How accurate is this triathlon predictor?
Physics-based bike modeling + fatigue adjustments. Typically within 3-5% when inputs are honest. Hilly races (Lake Placid, Wisconsin, St. George) improve in accuracy when you enter actual bike elevation.
What's a good W/kg for an Ironman?
Age-groupers race 2.5-3.1 W/kg. Sub-10 hr typically 2.8+. Elite pros 3.5+. For 70.3 aim 2.8-3.3.
How much carbs per hour during the race?
60-90 g/hr on the bike, 30-60 g/hr on the run. Total scales with race duration. Always rehearse fueling at race intensity.
Does elevation gain really slow my bike split?
Yes — ~2-3 min/hr added per 1000 ft of climbing at steady watts. Lake Placid's 6,625 ft costs 15-20 minutes vs. a flat course at the same W/kg.
Should I use CSS or a race swim time for the swim input?
Use pool CSS if you have it, then expect open water with a wetsuit to be slightly faster and choppy non-wetsuit swims to be slower. Sighting costs most age-groupers 3-6% on top.
How much time do transitions really cost?
Sprint and Olympic transitions run 1-3 minutes each; long-course transitions run 3-8 minutes. Over a season, transition practice is the cheapest time you will ever buy.
Why is my predicted run slower than my standalone pace?
Because the model applies a fatigue penalty from the bike. The harder you ride relative to your FTP, the larger the penalty gets.
VDOT calculator
Jack Daniels run pace predictor — set your triathlon run leg with the right Easy / Threshold / Interval paces.
FTP calculator
Cycling Functional Threshold Power and 7 Coggan zones — anchor every bike split.
Half Ironman (70.3) time predictor
Dedicated 70.3 calculator with realistic bike-to-run fade and transitions.
Ironman time predictor
Full-distance Ironman calculator — splits, transitions, fueling and pacing.
Breno MeloHead Coach · USA Triathlon, Road Runners Club of America, TrainingPeaksEmail me my race splits
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Discipline-wise split projection with transition allowance
Total = swim time + T1 + bike time + T2 + run time, where each leg is projected from the athlete's entered standalone ability and de-rated for the cumulative-fatigue effect of the preceding legs.
- Standalone abilities you entered are current and honest.
- You have done brick training, so the run de-rating is typical rather than severe.
- There is no peer-reviewed model for triathlon leg-to-leg carryover; the de-rating factors are coaching heuristics from this practice, not published research.
- Course profile, water temperature, wetsuit legality and draft rules change the outcome more than the model does.
Not externally validated. Calibrated against race files from athletes coached in this practice, and stated as such rather than dressed up as science.
Formula, constants and cited sources last verified on . Spotted something wrong? Email breno@brenoamelo.com and it gets corrected and dated.
How the splits are calculated
The bike leg uses a physics model: aerodynamic drag, rolling resistance and gravity are balanced against your sustainable power to solve for speed, then course elevation is applied.
Swim and run legs are scaled from your standalone paces with a fatigue penalty, because nobody runs their open 10K pace off the bike.
Transitions are added as fixed times, which is where most age-group predictions quietly go wrong.
References
Every physiological claim on this page traces to one of the primary sources below — the original paper, textbook or governing-body standard, not a secondary write-up.
- 01Riegel PS (1981). Athletic records and human endurance. American Scientist 69(3):285–290. JSTOR 27850427
- 02Allen H, Coggan AR, McGregor S (2019). Training and Racing with a Power Meter, 3rd edition. VeloPress, Boulder, CO — defines FTP and the seven-level power training zones. ISBN 978-1-937715-93-4
Using this page in your own work?
Copy a formatted reference below. If you are quoting a number from this page, please link back to it so readers can check the source and the date it was last reviewed.
Breno Melo, "Triathlon Race Predictor — Breno Melo Endurance Coaching", Breno Melo Endurance Coaching (last reviewed 18 May 2026). https://www.brenoamelo.com/calculators/triathlon
Predicting Your 70.3 Finish Time
How standalone splits translate to a race-day 70.3 clock.
Fueling the Long Ride
Bottle-by-bottle fueling for four hours and up.
FTP Explained for Cyclists
What FTP is, how to test it properly, and how often to retest.
Strength Training for Endurance Athletes
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