The bike is the longest leg of a half-distance race, and the one where it is easiest to spend money you'll need later. Most bad runs are decided before T2, usually in the first twenty minutes on the bike.
Why the bike decides the run
A half is roughly half bike by time. The run comes after nearly three hours of work, and your legs will spend whatever is left. Riding five percent too hard can save a few minutes on the bike and cost many more on the run, because a fade on the run is measured in minutes per kilometre, not seconds.
The trade is lopsided. That is the whole argument for riding evenly and slightly under what feels possible.
Pick a number before race day
Decide your target before you're standing in transition with adrenaline doing the maths. Use whatever you trust: power, heart rate, or perceived effort. Base it on your recent long rides, not your best day.
- Power: a share of your threshold that you have held in training for the full distance and then run off.
- Heart rate: a cap, with the caveat that heart rate drifts upwards as the day goes on.
- Effort: it should feel almost too easy for the first hour.
If the first hour feels heroic, the last hour will feel like an apology.
The first twenty minutes
You come out of the water with a high heart rate, fresh legs and everyone around you riding too hard. This is where most people overspend. Hold your number, let them go, and expect to see some of them again on the run.
Holding it for 90 km
Evenness matters more than the average. Surges on hills and out of corners cost more than they save. Ride the climbs a little above target and the descents a little below, and keep the spikes small.
Fuel is pacing too
An under-fuelled bike looks like a pacing problem on the run. Practise your race-day fuelling on long rides so that on the day it is routine, not an experiment. Check any specific carbohydrate targets with a sports dietitian.
Checking it afterwards
After the race, put the bike and the run side by side. If your run pace held within a few seconds per kilometre, the bike was about right. If it fell apart after 10 km, the bike or the fuelling probably wrote that cheque.
In LankFit, the goal split calculator gives you a bike target from your recent efforts, and the race detail shows the bike and run next to each other once the result is in.