The Bike at 70.3 Boulder: Rollers, Altitude, and Numbers You Need to Recalibrate

The Course in a Nutshell

90 km over two laps on the farm roads north of the Boulder Reservoir. Official elevation gain is 670 m (2,199 ft), but heads up: an older official page lists roughly 820 m (2,700 ft). Sources disagree; plan on the current number, but don't be surprised if your bike computer reads a bit more. The profile is all short rollers: punchy climbs, fast descents, no sustained ascents. The Diagonal Highway is closed to traffic; other sections have lanes marked off with cones, with narrow shoulders flagged in 2022 race reports. Hold your line, especially when passing.

Altitude Changes the Numbers

Boulder sits at about 1,620 m. Translation: higher heart rate at the same effort, lower sustainable power, slower recovery after every surge. If you're coming from sea level, your flatland watts don't apply here: cut your targets and start conservative. The flip side is thinner air: less aerodynamic drag, so times are still fast. Don't be fooled by your speed. Watch your watts and how you feel, not the speedometer. Multiple reports and the official race strategy guide hammer the same point: at altitude, spikes cost you double.

Pacing the Rollers

The temptation on rollers is to attack every climb and recover on the descents. At 1,600 m that's a recipe for blowing up on lap two. Better strategy: steady power, effort just above target on the climbs, surge over the top, then aero position and legs spinning on the descents. The first lap should feel easy. If you still have legs halfway through lap two, push then—not before. The descents are fast and the course is known for it: use them to recover without giving away time.

Heat and Exposure

The course is fully exposed. The start is cool, but Dam Road can already be very hot by mid-morning, and June highs hit 33°C and beyond. The bike is where you build (or wreck) your half marathon: drink and take in sodium from the first kilometers, not when you feel thirsty. Athletes who neglected hydration on the bike in 2022 paid with cramps from the first mile of the run, according to race reports.

Transition

In 2022 the racks were tight: bring the essentials, keep your spot organized, and memorize exactly where your bike is. The less stuff you have, the less time you lose.

What to Do Now

• Set power targets reduced from your sea-level numbers and test them in training, ideally at altitude or with HR-controlled efforts.
• Train for rollers: repeats on short climbs at steady power, no spikes.
• Practice your aero position on fast descents: you'll spend plenty of time there in Boulder.
• Write out your bike hydration-and-sodium plan and test it on a long ride in the heat.
• Prep a minimal transition setup: only what you'll actually use.