Half Ironman Pacing Strategy: Race Execution Guide

Half Ironman pacing requires extreme discipline on the bike—riding at 70-75% of FTP—to ensure you have enough energy for a strong half marathon finish.

The 70.3 distance punishes overpacing more severely than any other triathlon distance. This guide provides exact pacing targets for swim, bike, and run.

The Golden Rule of 70.3 Pacing

The race is won or lost on the run—but the run is determined by the bike.

Calculate Your Targets

Before race day, determine your pacing zones:

• Swim: CSS Calculator
• Bike: FTP Calculator
• Run: Recent 10K time + adjustment

Get overall time predictions: 70.3 Calculator

For full Ironman distance, check out our Ironman Bike Split Calculator which provides course-specific predictions.

Swim Pacing (1.9km)

Target Times

Pacing Strategy

Key Points

• Don't race the swim: It's just the warm-up
• Find clear water: Worth a few extra meters
• Draft if possible: Saves 10-15% energy
• Sight every 8-10 strokes: Swim straight

What 70.3 Swim Should Feel Like

• 85-90% of max swim effort
• Could go slightly faster but choosing not to
• Breathing controlled
• Exiting with energy for the day ahead

Bike Pacing (90km) - The Critical Leg

Power Targets

Heart Rate Guidelines (if no power)

Pacing by Segment

The Hardest Part: Not Going Too Hard

Signs you're riding too hard:

• HR creeping above Zone 3
• Breathing heavily
• Feeling "great" at 50km (you shouldn't)
• Passing lots of people (they may pass you later)

Signs you're pacing correctly:

• Feels "too easy" for first 60km
• Could go faster but choosing not to
• Stable power throughout
• Relaxed upper body

Dealing with Fast Starters

What happens: People fly past you early What you do: Nothing. Let them go. What happens later: You pass them on the run

Run Pacing (21.1km)

Target Times

Run Pacing Strategy

The First 3km: Critical Phase

What happens:

• Legs feel like concrete
• HR is high from bike
• Pace feels impossible
• Brain screams "stop"

What you do:

• START SLOW (really slow)
• Short, quick steps
• Walk the first aid station
• Trust that legs will come around

Example Pacing for 2:00:00 Goal (5:40/km avg)

When to Negative Split

You should run the second half faster if:

• You paced bike correctly
• Legs feel OK at halfway
• Nutrition is working
• Weather is favorable

Aim for: Second half 1-2 minutes faster than first half

Read more: Negative Split Triathlon

Common Pacing Mistakes

Mistake 1: Starting Bike Too Fast

What happens: "I feel great!" at 30km Result: Dead by 70km, walking the run Fix: Ignore power feelings; stick to numbers

Mistake 2: Chasing Other Athletes

What happens: Fast rider passes, you speed up Result: Riding above your ability Fix: Race YOUR watts, not others

Mistake 3: Not Adjusting for Conditions

Conditions requiring adjustment:

Mistake 4: Running First 3km at Goal Pace

What happens: Start at 5:40/km goal pace Result: Walk/shuffle by km 12 Fix: First 3km should be 30-45 sec/km slower

Mistake 5: Ignoring Nutrition

What happens: Skip feeds because "feeling good" Result: Bonk at km 15 of run Fix: Eat on schedule regardless of feeling

Race Day Execution Plan

Pre-Race

• Know your target power/pace numbers
• Write them on your hand or bike
• Have a backup plan if conditions change

During Swim

• Stay controlled
• Exit feeling fresh
• Think about T1

During Bike

• Settle in first 20km
• Check power/HR every 5 min
• Eat and drink on schedule
• Stay disciplined in final 20km

During Run

• Start very conservatively
• Walk first aid station
• Build through the race
• Empty tank in final 3km

Pacing Calculator Reference

Quick Bike Power Table

Quick Run Pace Table

Related Resources

• 70.3 Calculator - Race time prediction
• FTP Calculator - Bike power zones
• Negative Split Triathlon - Run pacing strategy
• Triathlon Bike Pacing - Bike execution details
• 16-Week Half Ironman Plan - Training program