IRONMAN 70.3 Boise
Course breakdown, historical weather, and field analysis.
Idaho's gem — river swimming and high desert riding
Boise, United States · July 25, 2026
IRONMAN 70.3 Boise takes athletes to Idaho's capital for a distinctly Western US racing experience. A river swim in the Boise River, a rolling bike through the high desert foothills, and a flat run along the Boise Greenbelt. The combination of river swimming, scenic desert terrain, and small-city charm makes Boise a unique stop on the US 70.3 calendar.
- Swim
- 1.9 km
- Lake
- Bike
- 91.5 km
- ↑513m · Rolling
- Run
- 21.2 km
- ↑19m · Flat
- Air Temp
- 18–33°C
- Water Temp
- 20°C
- Wind
- 12 km/h
- SE
Swim Course
Boise River swim — downstream in clear water
The swim takes place in the Boise River with a downstream current assist. The river offers clear, cold mountain water flowing from the Sawtooth Mountains. Water temperatures in late July can vary but are generally cool — a good wetsuit is recommended. The downstream current produces faster swim splits than effort would suggest.
- Downstream current assist in the Boise River
- Clear mountain water from the Sawtooths
- Cool river temperatures — good wetsuit recommended
- Faster swim splits than effort would suggest
Bike Course
High desert foothills outside Boise
The bike course heads into the rolling foothills outside Boise. The high desert landscape is distinctly Idaho — sagebrush, open views, and moderate climbing through dry terrain. The July heat at elevation can be significant, and the dry air means hydration needs are higher than humidity suggests. The roads are open and exposed to sun and wind.
- Rolling high desert terrain outside Boise
- Distinctly Idaho landscape — sagebrush and open views
- Dry heat at elevation — hydration crucial
- Open roads with sun and wind exposure
Run Course
Flat run along the Boise Greenbelt
The run follows the Boise Greenbelt — a tree-lined path along the Boise River through the city. The terrain is flat and the tree cover provides welcome shade from the July sun. The Greenbelt is beloved by locals, and the community support along the path is warm and genuine.
- Flat Greenbelt path along the Boise River
- Tree shade — welcome relief from July sun
- Community support along the path
- One of the more pleasant US 70.3 run courses
Race Day Conditions
High desert summer — hot, dry, and sunny
Late July in Boise means hot, dry conditions. Air temperatures can reach 35°C+ with very low humidity and intense sun. The dry heat is deceptive — athletes lose fluid rapidly without feeling as sweaty as in humid conditions. Aggressive hydration and sun protection are essential. The dry air does provide some relief compared to humid heat races.
Race Field Insights
How the Field Performs
Aggregated from 1,422 finishers (2025)
- Total Starters
- 1,593
- Finishers
- 1,422
- DNF Rate
- 10.7%
- Years of Data
- 2025
- Median Finish
- 6h 13m
Finish Time Distribution
How the Median Finisher Spends Race Day
What Each Pace Looks Like
Fast | Solid | Median | Back of Pack | Slow (P90) | |
|---|---|---|---|---|---|
| Swim | 35m 24s | 40m 33s | 45m 59s | 52m 19s | 58m 40s |
| Bike | 2h 23m | 2h 42m | 3h 01m | 3h 19m | 3h 36m |
| Run | 1h 34m | 1h 51m | 2h 11m | 2h 30m | 2h 52m |
| Finish | 4h 45m | 5h 29m | 6h 13m | 6h 55m | 7h 36m |
Related reading
Race Day Weather and What It's Really Doing to Your Pacing Plan
Performance starts dropping over 22°C and humidity makes it worse. How heat compounds across the bike and run — and why the bike hides it.
Read postYour Race Plan Isn't Generic — Why Course Intelligence Changes Everything
Same FTP on two different courses produces two completely different races. Elevation, wind, and shelter change what every watt is worth.
Read postPlan IRONMAN 70.3 Boise with Keiro
Get a complete pacing strategy for every discipline — built from this course, forecast weather, and your fitness.
Independent analysis. KeiroLabs is not the event organizer and is not affiliated with the race organizer.