IRONMAN 70.3 Boulder
Boulder, United States · June · IRONMAN
Why people love it
- Cool, clear reservoir swim with a rolling start
- Fast two-loop bike with mountain views and strong descents
- Strong aid stations and wet rags on the run
- Strong pro field and championship-style atmosphere
Watch out for
- Altitude of 1,655 m (5,430 ft): arrive two days early from sea level
- Hot, sunny, shadeless run up to 33 °C (91 °F), mostly packed dirt
- Single-entrance reservoir with remote parking and long post-race shuttle waits
- Run and bike routes change between years; check this year's map
Race
How racers feel about it, how well it is run, and how it treats a first timer. Counts for 27% of the overall score.
- Racer satisfactionLoved3.7
RaceRaves reviewers score it 4.3 out of 5 for swim and bike. A repeat finisher and others criticise the dirt run, heat and parking. · Medium confidence
- OrganizationAdequate3.2
Parking and shuttle problems and long post-race waits were reported in 2017, 2019 and 2024. Check-in and bike transport were praised in 2023. · Medium confidence
- First timer friendlyDemanding2.3
Altitude of 1,655 m (5,430 ft), heat to 33 °C (91 °F) and a shadeless dirt run. Local riders suggest an easier first 70.3. · Medium confidence
Course traits, not part of the score
- PR potentialAverage2.8
Fast bike, but altitude, heat and a slower dirt run cancel it out. · Medium confidence
- Course easeVery tough2.2
Altitude, heat to 33 °C (91 °F) and a dirt run. RaceRaves difficulty is 3.3 out of 5. · Medium confidence
Swim
Wetsuit odds, water temperature, calm, and the experience of the start. Counts for 15% of the overall score.
- Wetsuit legalCoin flip3.2
Water ranges 17-23 °C (62-74 °F). Wetsuits were borderline in 2019 and legal in 2021. · Medium confidence
- Water temperatureComfortable3.8
Three race reports describe cool but not cold water, 17-23 °C (62-74 °F). · Medium confidence
- Calm waterMostly calm4.0
Sheltered reservoir with no chop complaints. · Medium confidence
- Swim easeEasy3.8
Rolling start and easy sighting, though crowding and sun in the eyes on the way out are noted. · Medium confidence
- Swim experienceGreat4.1
Reviewers call the reservoir beautiful and the swim setup good. · Medium confidence
Bike
Road surface, closures, scenery and wind. Counts for 19% of the overall score.
- Road surfaceGood4.0
Reviewers praise the road condition. · Low confidence
- Road closuresPartly closed3.4
A 2019 reviewer felt unsafe beside fast highway traffic. · Low confidence
- Bike scenerySpectacular4.5
Reviewers praise the mountain views, and RaceRaves scores scenery 5 out of 5. · Medium confidence
- WindSome wind3.0
Wind built through the day on the bike and was strong on the 2021 run. · Low confidence
Course traits, not part of the score
- Bike speedFast4.0
Reports say the bike is fast, with diagonal highway and quick descents. · Medium confidence
- Bike flatnessMostly flat3.8
Rolling, with climbing on the first half of each loop. A 2011 poster estimated about 183 m (600 ft) per lap. · Low confidence
- Bike simplicityMostly simple3.8
Highway and country roads with fast descents. One reviewer felt unsafe near fast traffic. · Low confidence
Run
Crowds, aid stations, conditions underfoot and scenery. Counts for 13% of the overall score.
- Crowd supportDecent2.8
One reviewer said finish-line crowd support was lacking, though spectators shout at the swim exit. · Low confidence
- Aid stationsGood4.2
Reviewers say aid stations were strong, with wet rags on the run. · Medium confidence
- Run sceneryBeautiful3.8
Reservoir and mountain backdrop. · Low confidence
- Run conditionsHard1.9
Mostly packed dirt with no shade, heat to 33 °C (91 °F) and altitude. · High confidence
Course traits, not part of the score
- Run flatnessRolling3.0
The 2021 route had no major hills, but 2024 reports describe tough hills on the back half. · Medium confidence
Conditions
Air temperature, how predictable the weather is, setting, and spectating. Counts for 15% of the overall score.
- Air temperatureHarsh2.2
Highs near 33 °C (91 °F) in a dry, sun-baked venue. · High confidence
- Weather reliabilityVariable3.0
Rain beforehand in 2023, hot sun in 2024 and smoky wind in 2021. · Low confidence
- Venue beautyLovely4.4
Boulder Reservoir beneath the Flatirons and the Front Range. · Medium confidence
- Spectator friendlySome viewpoints2.6
Single-entrance reservoir, with parking and shuttle delays hampering spectators. · Low confidence
Course traits, not part of the score
- Low altitudeHigh altitude1.2
About 1,655 m (5,430 ft) above sea level. · High confidence
Stay and travel
Hotels, walkability, getting there, and the town around the race. Counts for 11% of the overall score.
- Hotel availabilityBook early3.2
Popular race in busy Colorado June season; book early. · Low confidence
- Hotel valueNormal2.6
Boulder is an expensive college town. · Low confidence
- WalkabilityMostly driving1.8
The reservoir sits outside town, with remote parking and shuttles. · High confidence
- Travel easeOne connection3.4
Denver International is about 65 km (40 mi) away and a rental car is needed. · Medium confidence
- LogisticsFiddly2.2
Single entrance, remote parking, shuttle lines and bike transport trucks. Improved in 2023. · High confidence
- Town and foodGood4.3
Boulder has a strong endurance-sports and food culture. · Medium confidence
Key facts
- Location
- Boulder, Colorado, United States
- Typical month
- June
- Latest or next date
- 12 June 2027
- Organiser
- IRONMAN
- Distances
- 1.9 km (1.2 mi) swim, 90 km (56 mi) bike, 21.1 km (13.1 mi) run
- Swim venue
- Boulder Reservoir (reservoir)
- Water temperature
- 17–23 °C (63–73 °F)
- Wetsuit
- Optional
- Swim start
- rolling
- Swim laps
- 1
- Bike laps
- 2
- Key climbs
- Rollers on the Diagonal and Hygiene Road
- Run climbing
- 60 m (195 ft)
- Run laps
- 2
- Run shade
- Little to none
- Air temperature
- 13–33 °C (55–91 °F)
- Humidity
- dry
- Altitude
- 1,655 m (5,430 ft)
- Nearest airport
- Denver International (DEN)
- Where to stay
- Boulder city centre, Longmont, Louisville
- Booking
- Popular race in a pricey college town; book early.
What racers and reviewers say
- Cyclizing: 2024 race reportRaced 2024 · blog · Mixed
Sixth Boulder start; finished in 5:07. Cold-ish swim with some crowding, a bike that climbs in the first half of each loop and descends fast, and a hilly dirt run in hot conditions. Logistics soured him: one entrance, shuttle lines, no toilets in the parking lot and a long bike-return wait.
“the bike course rips”
- Cyclizing: 2023 race reportRaced 2023 · blog · Mixed
Rain beforehand, then sun; clear swim in cool-not-cold water, strong bike, but dirt and rolling hills slowed the run and he missed a sub-5:00 (5:05). Shuttles from off-site lots fixed the parking problem and check-in was quick.
- Cyclizing: 2021 race reportRaced 2021 · blog · Mixed
Wetsuit legal, fast bike with diagonal highway and descents plus climbing, a penalty in a crowded pack, and a lollipop run with no big hills but a strong westbound headwind. Smoky haze and building wind.
- RaceRaves aggregated reviewsRaced 2019 · aggregator · Mixed
Overall 4.3 out of 5, scenery 5. Reviewers like the reservoir and mountain-view bike but say altitude bites sea-level athletes, there is no shade on the run, parking was messy and a 2017 traffic jam delayed the start.
“literally NO shade whatsoever”
- TrainingPeaks: How to Nail 70.3 Boulderarticle · Mixed
Coach's guide argues dry heat, no shade and a rolling profile matter more than altitude; plan a non-wetsuit swim in 21-23 C (70-74 F) water, arrive two days early, and expect dirt to cost 3-6 s per km (5-10 s per mile) on the run.
Show 3 more
- Colorado Triathlete 2015 recapRaced 2015 · article · Mixed
Pro-race recap noting altitude slows times and weather made the trail run harder than the previous year.
- Slowtwitch forum: Boulder vs BransonRaced 2011 · forum · Mixed
Poster who raced Boulder calls the bike fairly fast with gradual climbs about 183 m (600 ft) per lap and warns that the exposed dirt run, 90s F (32+ C) heat and altitude make the run tougher than it looks.
- Reddit r/triathlon: 'Opinions on Ironman 70.3 Boulder'Raced 2024 · reddit · Mixed
From a search snippet: a local rider says Boulder is hard thanks to the heat and a very competitive field, and suggests a first-timer may prefer an easier race (page not fetched).
Sources
Pages we used for facts and ratings. See how we rate.
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