Why the run is slower off the bike
Even at the same effort, running after cycling is 3–6% slower for most age-groupers. The reasons are neuromuscular, not psychological: the legs have been turning circles for hours and the stride takes a few kilometres to settle. The calculator applies that penalty explicitly instead of pretending the run is an open race.
Setting the penalty
If you have raced before, compare your triathlon run pace with your open pace over the same distance. The gap is your personal penalty. If you have not, start at 5% for an Olympic or 70.3, and 8% for an Ironman, where the bike leg is long enough to compromise the marathon.
What it means for pacing
The difference between a 4% and an 8% penalty over 10 km is about 1 minute 20 seconds. That is roughly the same as the gap between a good and a bad bike pacing decision — which is why the two tools belong together.
Frequently Asked Questions
Should I use my open 10K pace?
Only as a starting point. Add at least 3–5% for the bike, more if the course is hilly or hot.
Can I reduce the penalty?
Yes — bike pacing, brick sessions and a short run off the bike in training all help. So does starting the run conservatively.
Why is the penalty larger in an Ironman?
Because the bike is 180 km and the run is a marathon. Glycogen depletion and muscle damage accumulate, so the gap widens.
Related tools
Privacy & your data
SwimRunPace calculates everything in your browser. Distances, times and body weights are never uploaded — there is no account, no server-side record and no training history stored between visits.