How to Train for the Bike Leg of an Ironman or 70.3
Train the bike leg of a triathlon for the run that follows it. In a full Ironman most age-groupers ride the 180 km at around two-thirds to three-quarters of their FTP; in a 70.3, the 90 km at around three-quarters to four-fifths. The preparation is built on long, steady rides that grow towards race distance, one or two harder sessions a week at race-specific effort, short runs straight off the bike, and fuelling practised on every long ride — adapted to whether your race is flat, rolling or mountainous.
How hard to ride the bike leg
The bike is the longest part of the day, and the one that decides how you run. Riding it a few percent too hard costs far more time on the run than it saves on the bike, so the target is an effort you could hold for longer than the bike leg itself.
Measure it in power if you can: heart rate drifts upward over hours, speed depends on the wind and the gradient. Keep the effort even — the same watts on a rise as on the flat, rather than surging on every hill.
| Ironman (full) | IRONMAN 70.3 | |
|---|---|---|
| Bike distance | 180 km | 90 km |
| Effort, as a share of FTP | About 65–75 % | About 75–82 % |
| What follows | A 42.2 km marathon | A 21.1 km half marathon |
| Longest training ride | 4.5–6 hours | 2.5–3.5 hours |
The shape of a good preparation
Over the months before the race, the bike preparation moves from volume to specificity, then eases off:
- Base: steady endurance rides, building the weekly hours a little at a time (around 10 % a week, with an easier week every three or four).
- Build: one or two key sessions a week at race effort — long intervals at the pace you will hold on race day — and a long ride that grows towards race distance.
- Peak: rehearse race day — the long ride in race position, at race effort, with race fuelling, followed by a short run.
- Taper: in the last one to two weeks, cut the volume and keep a little intensity, so you arrive fresh.
Brick runs and fuelling
A brick is a short run straight after a ride: 10 to 30 minutes, at an easy to race-like pace. It teaches the legs to change from pedalling to running and tells you whether the bike effort was right. Event Coach plans the bike sessions and marks where a short run fits; your swim and run are yours to fit around it.
On race day you fuel the run on the bike. Practise eating and drinking on every long ride — the same products, at the same rate per hour — so the stomach is trained as well as the legs.
Train for your course's terrain
A flat course is ridden almost entirely in the aero position, so the long rides should be too. A hilly course asks for climbing efforts below threshold and for descending well. The course pages say which kind each race is, and two guides list them:
- The flattest and fastest Ironman and 70.3 bike courses
- The hilliest Ironman and 70.3 bike courses
- Ironman World Championship — Kona, United States, 9 October 2027
- Ironman Vitoria-Gasteiz — Vitoria-Gasteiz, Spain, 11 July 2027
- Ironman Lanzarote — Lanzarote, Spain, 15 May 2027
- Ironman Frankfurt — Frankfurt, Germany, 27 June 2027
- Ironman Cozumel 70.3 — Cozumel, Mexico, 26 September 2027
Training the bike leg indoors
A smart trainer makes race-effort work exact: in ERG mode the trainer holds the watts of the session, so a 2 × 45-minute block at race effort is ridden at race effort. Cycloscape's Event Coach turns your race, its date and your available hours into that plan, counts the rides you do outdoors from Strava, and — with Pro — lets you ride the race's own bike course on your trainer.
Frequently asked
How hard should I ride the bike leg of an Ironman?
Most age-group triathletes ride the 180 km at around 65–75 % of their FTP: an effort you could hold for longer than the bike leg, so the marathon is still possible. Keep it even rather than surging on the hills.
How hard should I ride the bike leg of a 70.3?
Around 75–82 % of FTP for most age-groupers over the 90 km — hard enough to race, controlled enough to run a half marathon after it.
How long should my longest training ride be?
For a full Ironman, around 4.5 to 6 hours; for a 70.3, around 2.5 to 3.5 hours — ridden at race effort in the final weeks, with race fuelling and a short run after.
What is a brick session?
A short run straight after a ride, usually 10 to 30 minutes. It trains the switch from cycling to running and shows whether your bike effort was right.
Does Cycloscape plan my swimming and running?
No. Event Coach prepares the bike leg — workouts, pacing and the course — and marks where short runs fit; plan your swim and run with your own coach or programme.