The Ironman run is where races are won and lost. And in most cases, the run is determined entirely by what happened on the bike. Pacing errors in the first 112 miles are the #1 cause of blown marathons, DNFs, and disappointing finish times.
Here are the five most common Ironman pacing mistakes — and how to fix them.
Mistake 1: Going Out Too Hard on the Bike
The excitement of race day, fresh legs, and a fast early pack will tempt you to ride harder than planned. Resist it. Every watt above your target power in the first 30 miles costs you exponentially more on the run.
Fix: Set a power ceiling for the first 30 miles and treat it as a hard rule. Your target watts should feel embarrassingly easy early on.
Mistake 2: Riding to Heart Rate Instead of Power
Heart rate is a lagging indicator. It responds to heat, caffeine, excitement, and fatigue — not just effort. Athletes who pace by heart rate on the bike often overcook themselves before their HR even reflects it.
Fix: Use power as your primary pacing tool. Heart rate is useful context, not the governor.
Mistake 3: Ignoring Elevation and Wind
Flat power on a hilly course means you're going too hard on climbs and coasting on descents. Variable power on a windy course means you're fighting the wind instead of managing it.
Fix: Use normalized power (NP) as your target metric, not average power. Allow power to vary with terrain while keeping NP on target.
Mistake 4: No Fueling Plan
Athletes who wing their nutrition on race day pay for it at mile 18 of the run. Ironman fueling requires 60–90g of carbohydrate per hour on the bike, consistent sodium intake, and a hydration strategy matched to conditions.
Fix: Build and practice your exact race-day fueling plan in training. Nothing new on race day.
Mistake 5: Starting the Run Too Fast
The first mile of the Ironman marathon feels easy. Your legs are fresh from the bike, the crowd is loud, and your pace feels controlled. It isn't. Starting even 15 seconds per mile too fast in the first 10K will cost you minutes in the final 10K.
Fix: Run the first 6 miles at a pace that feels almost too easy. Your race starts at mile 18.
Race Execution Is Coachable
Every one of these mistakes is preventable with proper preparation, data-informed training, and a race execution plan built by someone who's been there. The ANC Performance System™ includes race-specific strategy for every athlete — not just a training plan.