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Race IntelligenceBoise, United States

IRONMAN 70.3 Boise

Know your day before you race it.

Enter four numbers you already train with. You get a likely finish range, target paces and watts, and how I would race this course.

Race day
24 July 2027
Swim
1.9 km
Bike
90 km
Run
21.1 km

Published route evidence. Final 2027 route pending. Checked 14 Sept 2026.

01 Race Card

Build my Race Card

Your first range uses conservative assumptions. Add optional evidence to make it more specific. It is calculated in your browser and saved only on this device.

Your numbers
Distance unit
Weight unit
You and this race
Sharpen your range with more detailOptional. Recent swim, bike and run results, equipment and transitions.

Add only the evidence you have. Every control changes a discipline range, its uncertainty, or an execution-risk explanation.

Swim evidence

Replaces the broad pool-to-open-water assumption.

Bike and equipment

These replace broad mass, aerodynamics, tyre, and power-to-speed assumptions.

Run evidence

A recent effort and honest durability/acclimation answers refine the post-bike run.

Race execution

Transition proficiency changes the T1/T2 range and how wet conditions are treated.

02 The course

What Boise actually gives you

You swim in the calm waters of Lucky Peak Reservoir at Barclay Bay, ride a 90 km course that opens with a sweeping downhill before a rolling, scenic tour of rural Boise roads and neighbourhood streets into a downtown finish, then run a flat, shaded two-loop route along the Boise River Greenbelt Trail. Settle into a number after the downhill start and the run stays available.

Show distances in

Swim

1.9 km

Calm Reservoir Swim

Setting
Lucky Peak Reservoir, starting and finishing at Barclay Bay

A calm, clear reservoir swim gives a controllable opening.

Source: 2027 current route

Bike

90 km

Downhill Start Into a Rolling, Scenic Tour

Setting
rural Boise roads and neighbourhood streets, finishing downtown

A sweeping downhill exit from the reservoir sets an early pace trap before a rolling tour of rural roads and neighbourhood streets into downtown.

Source: 2027 current route

Run

21.1 km

Flat, Shaded Two-loop Greenbelt Trail

Layout
2 loops
Setting
the Boise River Greenbelt Trail, finishing in downtown Boise

A flat, shaded two-loop greenbelt trail rewards legs that settled into a number rather than chasing the bike's fast opening descent.

Source: 2027 current route
Where these course facts come from

These facts come from the organiser’s latest published material: swim, 2027 current route; bike, 2027 current route; run, 2027 current route. They describe the character of the course. They do not confirm the final 2027 route.

03 Race plan

How I’d want you to race it

One job for each part of this course. The distance markers tell you when the job changes. The course tells you why.

Swim

Settle in the reservoir

  1. 0–300 m

    The start

    Find clean water early

    The reservoir's calm, clear water rewards an honest, controlled opening.

    • Seed honestly
    • Settle into rhythm

Bike

Don't chase the downhill start

  1. 0 km–45 km

    The downhill exit

    Don't chase the fast start

    A sweeping downhill out of the reservoir tempts an early charge. Settle into your target number rather than riding the descent's speed.

    • Cap opening effort
    • Fuel early

  2. 45 km–90 km

    Into rural Boise

    Protect the run

    Finish planned nutrition through the rolling roads and neighbourhood streets before the downtown finish.

    • Stay patient
    • Finish planned nutrition

Run

Use both loops

  1. 0 km–10.5 km

    First loop

    Start controlled

    Let the shaded greenbelt opening feel easy, not fast.

    • Easy first aid station
    • Check posture

  2. 10.5 km–21.1 km

    Second loop

    Use what you saved

    Only progress once the first loop has held together.

    • Stay tall
    • Choose the last move late

04 Race week

What I would keep an eye on

There is no useful 2027 forecast this far out. For now, past race dates give us a point of reference. Closer to the race, the forecast will tell us whether the plan needs changing.

Forecast statusToo early for a forecast

A race-day forecast is not meaningful yet; check back closer to the event.

Temperature
18.7–34.2°CDew point centred on 5.8°C
Wind and gusts
7.2 km/hGusts up to 33.1 km/hPrevailing direction NW
Rain likelihood
Up to 15%Wet-surface uncertainty retained

Historical baseline, 2019–2025 · Open-Meteo historical archive · Updated 2026-09-14.Historical comparison only. This is not a forecast for 2027.

05 Method

What goes into your range

Your CSS, FTP, weight and run threshold create the first range. Open-water, bike, run and execution evidence can replace broad assumptions. Course data and the historical conditions baseline shape every simulation.

  1. Your numbersCSS · FTP · weight · run threshold
  2. This raceDistance · water type · elevation · exposure
  3. Your Race CardFinish and discipline ranges, with target paces and watts

Confidence is built from four inputs

Athlete evidence
Builds with recent open-water, bike and run efforts
Bike setup
Builds with equipment, mass, aero and tyre detail
Course evidence
Partial while the 2027 route is unconfirmed
Race-week conditions
Historical baseline until a forecast is useful
How the model works

It starts with the targets in your Race Card, then samples the parts of a 70.3 that vary: open-water pace, transitions, bike speed at the planned power, and the drop in run performance after the swim and bike. Repeating that calculation produces a likely range rather than a single heroic number.

The current time calculation uses this race’s published distances, or standard 70.3 distances where none are published, with the available course headings, elevation and exposure evidence. Weather scenarios vary temperature, dew point, wind, gusts, rain and water conditions together. Unknown route detail stays visible as uncertainty rather than false precision.

It is not predicting your exact finishing time, placing, or race-day weather. It answers a narrower question: given the plan and the information we have, what range of day is plausible, and where is the uncertainty coming from?

Confidence is not a permanent “low”. It is recalculated across four separate inputs:

  • Your evidence: consistent inputs and recent race-like swim, bike, and run results.
  • Bike setup: measured or specified aerodynamics rather than a broad prior.
  • The course: verified distance and route character, including elevation and technical sections.
  • The conditions: a current forecast is more useful than a historical comparison.

It starts low when those inputs are broad. It can become moderate or high as the evidence improves. A narrower range means better information, not a guarantee.

06 Next steps

If Boise is your race

Your range is built on today’s numbers. The months of training before race day decide what those numbers become.

The work from here.

Self-guided routeHalf-distance training plansTraining plans for the durability this course asks for.See the plans Personalised routeWork with me on the whole buildCoaching when you want the plan and race decisions joined up.See coaching

Further reading

ArticleHow to pace a 70.3 so you can still runThe longer version of the pacing logic behind this Race Card.ArticleFix the first ten minutes off the bikeUseful when an overridden bike opening needs to become controlled running.

Evidence

Sources and verification

Course status: Partially verified. The organiser’s descriptions and latest published route profiles are in use. The final 2027 route is not yet confirmed. Last checked 2026-09-14.