— Target Bike IF
— Target Normalized Power
— Target Average Power
— Power as % of FTP
— Bike Pacing Risk
— Target Run IF
— Target Run Pace
— Run Pacing Risk
— Target Swim IF
— Target Swim Pace
— Total Race TSS
— Race Pacing Category
Methodology
This calculator reverses the standard TSS formula to derive power targets from a TSS budget. The core equation is TSS = hours × IF² × 100, where IF (Intensity Factor) = Normalized Power / FTP. Solved for IF: IF = sqrt(TSS / (hours × 100)). From IF we get Normalized Power (NP = IF × FTP), and then Average Power = NP / VI, where VI (Variability Index) accounts for course profile: flat = 1.02, rolling = 1.05, hilly = 1.07. Run rTSS uses the same squared-IF formula applied to pace, where threshold pace defines IF = 1.0. Swim sTSS uses a cubed formula (sTSS = hours × IF³ × 100) because water resistance scales with velocity to the third power — a fundamentally different physiological cost curve than cycling. Formula sources: Coggan & Allen, Training and Racing with a Power Meter (3rd ed.); Friel, The Power Meter Handbook. TSS targets validated against race data: ~280 TSS for full Ironman bike (TrainingPeaks guidelines; Dalzell Coaching race analysis); ~170 TSS for Ironman 70.3 bike.
FAQ
Why is 280 TSS the standard target for the Ironman bike?
The 280 TSS figure for a full Ironman bike leg emerged from convergent coaching experience across multiple frameworks: Friel's threshold-based periodisation, Coggan's power zones, and TrainingPeaks race-data aggregation. Race analysis by Dalzell Coaching found that athletes who finished sub-10 hours typically produced 265–290 TSS on the bike. The most referenced data point is Pete Jacobs's 2012 Ironman World Championship win — he rode approximately 285 TSS at an IF of 0.79. The physiological rationale is glycogen: above ~285 TSS (depending on individual glycogen capacity and fat oxidation ability), the glycolytic cost of the bike leg compromises the marathon's pace. The 250–285 range is the sweet spot for competitive age groupers because it is fast enough to produce a competitive split but conservative enough to leave glycogen and muscle integrity for the run. Below 250 TSS is typically too conservative for athletes targeting sub-12 hours.
Is 185 TSS the right target for an Ironman 70.3 bike?
185 TSS is the aggressive end of what most coaches recommend for 70.3, suitable for experienced athletes with strong run backgrounds and excellent fat oxidation. The defensible range is 165–185 TSS. At 2.5 hours of bike time, IF 0.82 produces 168 TSS; IF 0.86 produces 185 TSS — that 0.04 IF difference translates to roughly 8–10 watts at 250W FTP, which feels small but compounds meaningfully over 90+ km. First-timers and athletes who struggle on the 70.3 run should target 165–170 TSS. Athletes with significant 70.3 experience and run economy under 4:30/km can push toward 182–185 TSS safely. The key validation is whether your target pace in the last 5 km of the run holds — if it degrades sharply, your bike TSS was too high.
What is Intensity Factor and why is it the most important Ironman metric?
Intensity Factor (IF) is the ratio of Normalized Power to FTP: IF = NP / FTP. An IF of 1.0 means you rode at your threshold — a pace you can sustain for roughly one hour at maximum effort. For a 4.5–6 hour Ironman bike, sustainable IF ranges are approximately 0.70–0.75 for mid-pack age groupers, 0.73–0.78 for competitive age groupers, and 0.76–0.80 for professionals and elite amateurs. IF matters more than average power because it integrates the metabolic cost of variability through Normalized Power's 4th-power algorithm. Critically, IF should be paired with Variability Index (NP / average power). Keep VI below 1.05 on flat to rolling courses — riding steady rather than surging on rises. A VI of 1.08 or above signals you are burning substantially more glycogen per kilometre than your average power suggests, which will destroy the run.
Why does course profile change my power target?
Normalized Power weights intensity non-linearly using a 4th-power algorithm: a hard 30-second surge costs metabolically far more than its average contribution suggests. On hilly courses you are forced into repeated surges on climbs, which drives NP above average power even if you try to ride smoothly. The Variability Index (NP / avg power) captures this: flat courses produce VI of ~1.02, rolling courses ~1.05, hilly courses ~1.07 or higher. The consequence is that to hit the same TSS on a hilly course, you need less average power than on a flat course — the surges do the 'extra' metabolic work for you. Specifically, if your target NP is 185W and VI is 1.07, your target average power is 185 / 1.07 = 173W. On a flat course with VI 1.02, that same 185W NP requires 185 / 1.02 = 181W average. Riding too high an average on a hilly course is one of the most common Ironman pacing errors.
How accurate are the run and swim TSS estimates?
Bike TSS is the most validated of the three disciplines, backed by decades of power meter data and extensive race-outcome correlation research. Run rTSS uses the same squared-IF framework, with threshold pace defining IF = 1.0, but is derived from pace rather than direct power — it is directionally valid but less precise because running efficiency, terrain, and fatigue non-linearly affect metabolic cost. Swim sTSS applies a cubed-IF formula reflecting water resistance physics, but has the least empirical validation because swim power measurement is uncommon. Use bike TSS targets as your primary race planning constraint; run and swim outputs here are guidance for total-race TSS budgeting rather than precise execution numbers. A practical rule: if your total race TSS (swim + bike + run) exceeds 550 for a full Ironman, review your individual splits — one discipline is likely overcooked.
How does this calculator compare to Best Bike Split?
Best Bike Split (BBS) is a full physics simulation: it models elevation profiles, wind speed and direction, coefficient of drag (CdA), rolling resistance, and drivetrain efficiency, producing segment-by-segment power targets for a specific course. This calculator operates at a higher strategic level: it translates a TSS budget into target watts without course-specific physics. The two tools are complementary, not competing. Use this calculator during race planning (6–12 weeks out) to set your IF and TSS budget, validate your fitness against the target, and have a coherent conversation with your coach. Then load your target watts into Best Bike Split 2–3 weeks out to generate a course-specific execution file. If BBS recommends significantly different numbers, trust BBS for execution but revisit your TSS budget — the discrepancy usually means the course profile is more or less demanding than your VI assumption.
Results are estimates based on TSS modelling and coaching consensus. Individual physiology, race conditions, heat, altitude, and fatigue resistance all affect real-world performance. Use as a strategic planning framework, not a rigid race-day script. Consult a certified triathlon coach for personalised pacing strategies.
