The same athlete, across the four distances
With your reference time scaled to each distance and the typical bike intensity of each, this is how the penalty grows as the day gets longer.
| Race | Typical intensity | Penalty | Seconds per km |
|---|
Home›Triathlon›Run off the bike
How much slower will you run off the bike?
Nobody runs their fresh-legs pace in a triathlon. Enter your personal best over that distance and the intensity you plan to ride at, and this calculator tells you how many seconds per kilometre you will lose and what that adds up to.
The run
The bike leg before it
88 %
Fine tuning
You will run slower by
—s / km
Penalty
—
Your pace
—
Run time
—
What riding harder costs you
| Intensity | Penalty | Pace | Run time |
|---|
Why you run slower after riding
The short answer: you arrive at the run with part of the tank empty and with legs doing a movement that is not theirs. The long answer has four pieces, and only one of them is fixed by training more.
Glycogen. You have been burning carbohydrate for one to five hours before taking your first step. In an Olympic distance race the impact is moderate; in an Ironman it is the dominant variable and explains why the marathon so reliably falls apart after kilometre 25.
The motor pattern. Pedalling is concentric, cyclic and impact-free, at 85 to 95 revolutions. Running is eccentric, with impact, at 170-180 steps. The first minutes are a change of program: the stride comes out short, the ankle stiff and the cadence low. That part does respond to training, and it is exactly what bricks address.
Blood distribution. After the bike, much of the flow is still in the pedalling muscles and in the skin shedding heat. Running efficiency drops while the body redistributes, which takes five to ten minutes.
Accumulated heat. You start running with an already elevated core temperature and the midday sun ahead of you. That is why the penalty rises so much in hot races, and why it should be built into your pacing plan.
How it is calculated here
The penalty is built on a base that depends on distance and is scaled by the intensity you rode at, your experience running off the bike and the heat:
penalty = base(distance) × (IF / reference IF)³ × experience × heat
base: 5 km 6 % · 10 km 8 % · 21.1 km 10 % · 42.2 km 18 %
reference IF: sprint 92 % · Olympic 88 % · 70.3 80 % · 140.6 70 %
The cubed exponent is what matters. Riding 10 % above the reference intensity does not worsen your run by 10 %: it worsens it by 33 %. That non-linearity is why the "ride hard and hang on" strategy almost never works, and why the five minutes you gain pedalling turn into fifteen lost running.
What actually reduces it
Three things work, in this order. First, ride easier: the biggest lever and the most uncomfortable to accept. Second, train the transition with regular bricks, even short ones: twenty minutes of running after a bike session does more than an isolated long run. Third, rehearse your fuelling on the bike, because whatever you fail to eat there you will miss at kilometre 30.
What does not work is trying to force the pace in the first kilometre. Your legs take five to ten minutes to become yours again: those who go out at target pace from the first step usually pay for it later.
Frequently asked questions
How much slower do you run in an Olympic triathlon than in a standalone 10 km?
Between 6 % and 12 % for most people, that is 15 to 35 seconds per kilometre. A 42-minute 10 km runner usually finishes between 45 and 47 minutes in an Olympic distance race, depending on how hard they rode.
And in an Ironman compared with my marathon best?
Between 15 % and 30 %. A 3 h 30 min marathoner rarely goes under 4 h 05 min in an Ironman marathon, and if they overcooked the bike they can go beyond 4 h 30 min.
Are brick sessions useful or just a fashion?
They are useful, but for less than people think. They improve the motor pattern and the head in the first kilometres, and that gain is real. They do not change the glycogen you have burned or the blood still in your quadriceps: against that, only riding easier and fuelling better works.
Why do the first kilometres feel so strange?
Because the stride carries over from pedalling: short, stiff and at low frequency. It usually lasts five to ten minutes. Deliberately raising your step cadence coming out of T2 shortens that period.
How much does heat affect it?
Far more than in a standalone run, because you arrive with an already elevated core temperature. Above 28 degrees the penalty can nearly double compared with a cool day, and in long distance racing it is the usual cause of DNFs.
What if I want the whole race and not just the penalty?
Use the race time predictor, which calculates all three splits and the transitions with the same penalty model.
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This calculator is an informational estimate and does not replace a coach or a laboratory test. Nothing you type ever leaves your browser.