IRONMAN · Pembrokeshire · 19 Sept 2027
How to train for IRONMAN Wales
Tenby is nicknamed the Iron Town and its race has a reputation for hills. The reputation is earned. It is also a trap, because a rider who trains only to climb meets a bike course whose largest blocks of time are flat. The engine reads the steepest sustained climb on the bike at 623 m and 7.7 percent, and that climb holds about 1 percent of the bike leg.
The hills are still there. The bike climbs 1819 m and the run climbs 534 m, which across 42.2 km is more metres for every kilometre than the bike manages across 178 km. What the reputation gets wrong is the order the bills arrive in, and which one you can still afford to pay.
By Kian Briel, founder. Analysed by engine 1, updated
What is actually on the road
The organiser's own course files, drawn the way the Event Analyzer draws a member's race.
- Swim3.82 km139 m upCourse file
- Bike178 km1,819 m upCourse file
- Run42.2 km534 m upCourse file
Start in the water. The swim is 3.8 km off the sandy North Beach at Tenby, logged by the organiser at 17 C in 2025 and 17 C in 2024. Then a kilometre on foot from the water to transition in the Seafront Car Park, up the zig zag ramp. The bike covers 178 km through Pembrokeshire Coast National Park for 1819 m of climbing, and the organiser singles out the Saundersfoot climb as the place the crowd pushes you up. The run is 42.2 km in the town centre, past the medieval town walls and the beachfront, for 534 m of climbing.
Now read the profile. The two stretches that swallow the most bike time are both flat, and each one holds about 6 percent of the bike leg on its own. The steepest sustained climb holds about 1 percent. Wales does not hurt you in one place. It hurts you in a thousand small ones, and that is a different thing to train for.
Course shape by distance
- Flat 76%
- Climbing 12%
- Descending 12%
The longest stretches
- Bike, flat12 km6% of the bike
- Bike, flat10.9 km6% of the bike
- Bike, climbing0.62 km1% of the bike
Each row is one unbroken stretch of the course that keeps the same shape the whole way. The number is how much of that leg you spend inside it, and it comes out the same whether you are fast or slow.
What this course asks of each leg
Twelve training dimensions scored for each leg against its own course, the way the Event Analyzer scores a member's race.
Endurance that keeps its shape under repetition. Aerobic endurance leads the bike at 95 and aerobic durability leads the run at 96. Those two sit at the top of the cross-leg ranking because the ranking weights every score by how much of the day its leg takes, and the bike takes more of this day than anything else on it.
The swim is where that weighting gets misread. Muscular endurance scores 99 there, the highest single number anywhere on this course, and it still lands twentieth once the swim's share of the day is applied to it. A 99 across 1:20:18 is worth less than a 93 across 6:45:56. The swim is not unimportant. It is simply not where the day is won.
Make it concrete. A Trained athlete comes home in 12:33:38 from an input of 3.03 W/kg at 75 kg, riding at 159 W and running from an input of 5:06 /km threshold pace. The Competitive band comes home in 10:48:52 at 218 W. Their bikes are 6:45:56 against 5:50:42. Their runs are 4:17:24 against 3:38:43. Those are reference times for a 75 kg reference athlete, not forecasts for anyone reading this page.
Heat is not the argument here. Environmental resilience scores 20 on every leg and the engine marks that reading low confidence, which is the honest label, because it has the event baseline and nothing else. The organiser's own record shows a high of 18 C against a low of 16 C in 2025, and a high of 22 C against a low of 12 C in 2024. Two very different September days.
- Muscular endurance99
- Aerobic endurance95
- Aerobic durability90
- Threshold durability87
- Fueling resilience85
- Technical skill73
- Threshold capacity55
- Strength / force40
- High-intensity capacity30
- Environmental resilience20
- Anaerobic capacity15
- Sprint power0
Nymiva reads what you can already show, from your own data
Connect your training history and the Focus Lab scores the same twelve dimensions this course demands against where you sit today. The gap between the two is what you train.
- MeasuredFrom your thresholds and testsThreshold power, threshold pace, critical swim speed and field tests you have done. The dimensions they can carry are scored directly.
- EstimatedFrom your training historyConnected activities are read for what they prove: long efforts, late-session fade, repeated hard work, fueling on long days. Each score says how it was read.
- ProxyFrom a stand-in, and named as oneWhere only an indirect signal exists, the score carries the proxy it came from and a lower confidence, never a number dressed as a measurement.
- UnmeasuredHonestly blankA dimension nothing in your data can answer stays unmeasured. It is never a zero, and the plan does not pretend to know it.
Every dimension ends in one word
- Develop the course asks more than you can show
- Maintain close enough to hold at the minimum dose
- Covered nothing to build here
- Unmeasured the course needs it, your data cannot say yet
Nymiva scores the same twelve dimensions on both sides of the comparison. The course is scored from its file, the gradients, the corners and the distance, and an athlete is scored from their thresholds and their connected training history. Every score carries how it was read and how confident that reading is. A dimension becomes a gap only where the course asks for more than the athlete can show, and the gap is then weighted by how much of the day it fills, which is why a bike score outranks a swim score here.
This page holds none of your data. The season on it assumes the simplest case, that your gaps sit where this course makes its biggest demands, and it runs 28 weeks with 3 developmental blocks. Your own season would start from your numbers instead. It would order its blocks differently and hold different capabilities at maintenance while it did.
Train the bike to protect the run
Which demands matter most across the whole race. A leg's demand counts for as much of the day as that leg takes, so a score of 85 on the bike outweighs the same score on the swim.
- 01Aerobic enduranceBike leg, 54% of the day95 × 54%51
- 02Aerobic durabilityBike leg, 54% of the day94 × 54%51
- 03Muscular enduranceBike leg, 54% of the day93 × 54%50
The bike takes 54% of the Trained reference band’s day, so its demands carry the most race weight. What the bike leaves in the legs is what the run gets.
Which demand gets a block, and when
The engine freezes one lead focus per sport on every developmental block, holds the rest at maintenance, and verifies before it reprioritises.
An illustration, not your plan. This page has none of your data, so the season below is the engine’s answer to one stated assumption: that your gaps line up with what IRONMAN Wales demands. Your own season is built from your history, your thresholds, the days you can train and the races you have entered, and it will differ from this in its priorities, its sessions and its load.
- 01Bike muscular endurance, a practice block4 weeks
- 02Bike aerobic durability, a practice block6 weeks
- 03Bike aerobic endurance, a development block9 weeks
In the order the allocator places them, general first, most race-like last.
- Week 1PrepPrep
A lead-in week. It develops nothing by design.
- Weeks 2 to 9Foundation 2Closes with a recovery week
- PrioritySwim muscular endurance
- PriorityBike aerobic endurance
- PriorityRun aerobic durability
- SupportBike aerobic durability
- SupportRun aerobic endurance
- SupportSwim aerobic endurance
- SupportBike muscular endurance
- SupportRun muscular endurance
- SupportSwim aerobic durability
- SupportSwim threshold durability
- SupportBike threshold durability
- SupportRun fueling resilience
- Weeks 10 to 17Event shaping 1Closes with a recovery week
- PrioritySwim threshold durability
- PriorityBike threshold durability
- PriorityRun fueling resilience
- SupportSwim muscular endurance
- SupportBike aerobic endurance
- SupportBike aerobic durability
- SupportRun aerobic durability
- SupportRun aerobic endurance
- SupportSwim aerobic endurance
- SupportBike muscular endurance
- SupportRun muscular endurance
- SupportSwim aerobic durability
- Weeks 18 to 25Event shaping 2Closes with a recovery week
- PriorityBike aerobic durability
- PriorityRun aerobic endurance
- PrioritySwim aerobic endurance
- SupportSwim muscular endurance
- SupportBike aerobic endurance
- SupportRun aerobic durability
- SupportBike muscular endurance
- SupportRun muscular endurance
- SupportSwim aerobic durability
- SupportSwim threshold durability
- SupportBike threshold durability
- SupportRun fueling resilience
- Weeks 26 to 27PeakPeak
The taper. Load comes down toward the race, content stays specific.
- Week 28RaceRace
Race week.
Held at maintenance between blocks
- Bikemuscular endurance, aerobic durability, aerobic endurance, threshold durability, fueling resilience
- Swimaerobic endurance, aerobic durability, threshold durability, muscular endurance, technical skill, fueling resilience
- Runaerobic endurance, aerobic durability, threshold durability, muscular endurance, technical skill, fueling resilience
Touches scheduled by each capability’s own decay, at a fraction of its development dose, so earlier work is still there on race day.
The sessions the blocks are built from
One entry per kind of work the block trains, at the intensity that work is meant to be done at. Where the same work runs at several lengths, the entry shows the span it grows across rather than one entry per length.
- Foundation 2 · Weeks 2 to 936 to 38 min
5 x 4 min at Zone 3, 0.4 min easy between
SwimPace, Zone 3Trains muscular endurance - Foundation 2 · Weeks 2 to 975 to 240 min
150 to 210 min at Zone 2
BikePower, Zone 2Trains aerobic capacity - Foundation 2 · Weeks 2 to 940 to 270 min
180 to 210 min at Zone 3, then 30 min at Zone 4
BikePower, Zone 3Trains aerobic capacity - Foundation 2 · Weeks 2 to 975 to 130 min
70 min at Zone 2, then 40 min at Zone 3
RunHeart rate, Zone 2Trains aerobic durability
12× rolling-course surges
2 min at Zone 5, then 2 min at Zone 5, then 2 min at Zone 5, then 2 min at Zone 5, then 2 min at Zone 5, then 2 min at Zone 5, then 2 min at Zone 5, then 2 min at Zone 5, then 2 min at Zone 5, then 2 min at Zone 5, then 2 min at Zone 5, then 2 min at Zone 5, 9.8 min easy between
Compiled by the deterministic course compiler from the organiser’s file: the course’s one repeatable requirement, rehearsed at a dose the progression allows.
- Bike
- 156 min
- Trains threshold durability
- Supports muscular endurance
- Supports high intensity capacity
28 weeks, laid out backwards from race day
The shortest runway Nymiva builds for this event type, with its blocks, recovery weeks, taper and race week in place.
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- Prep
- Foundation
- Event shaping
- Peak
- Race
- Recovery week
Your own season carries these same phases on your own dates, with the load solved from your fitness and the days you can train, and it changes when your data does.
What each level does on the day
Reference finish times per peer band, the pacing plan the model holds each band to, and where the day is decided.
| Band | Swim | Bike | Run | Finish |
|---|---|---|---|---|
| Recreational2:11 /100m critical swim speed · 2.47 W/kg at 75 kg · 6:08 /km threshold pace | 1:34:47 | 7:33:07 | 5:09:33 | 14:27:27 |
| Trained1:51 /100m critical swim speed · 3.03 W/kg at 75 kg · 5:06 /km threshold pace | 1:20:18 | 6:45:56 | 4:17:24 | 12:33:38 |
| Competitive1:36 /100m critical swim speed · 4.15 W/kg at 75 kg · 4:20 /km threshold pace | 1:09:27 | 5:50:42 | 3:38:43 | 10:48:52 |
| Elite1:26 /100m critical swim speed · 5.27 W/kg at 75 kg · 3:50 /km threshold pace | 1:02:13 | 5:19:58 | 3:13:28 | 9:45:39 |
Pacing plan
- 0 km0.3%27.7 km/h1:27
- 0.67 km-3.5%46.7 km/h0:33
- 1.09 km0.4%27.2 km/h11:56
- 6.5 km3.9%13.7 km/h2:26
- 7.05 km-0.3%30.7 km/h23:25
- 19.1 km4.2%13 km/h4:43
- 20.1 km-1.8%38.5 km/h1:12
- 20.9 km4.4%12.6 km/h2:22
92 more segments in the full plan.
- Run: reach 4:20 /km and this course gives back 1:44:46.
Where it is decided
On the run, and not on the climb you have been worrying about.
The bike sets the terms and the run settles them. 534 m across 42.2 km is more climbing for every kilometre than the bike asks, it arrives last, and it arrives on legs that have already spent 6:45:56 in the National Park.
Aerobic durability is the run's highest demand at 96 and nothing else on that leg comes near it. The question the day asks is whether that durability is still there after the bike, and the engine answers it by spending its developmental weeks on the bike. Every demand that earns a block of its own in the season on this page is a bike demand. The run is defended by how the bike was ridden, hours before anybody laces up.
Getting it wrong
The first mistake is arithmetic done on the elevation line. A rider sees 1819 m, decides this is a climber's race, and spends the winter on repeats. The course reading says something else. Strength scores 54 on the bike where aerobic endurance scores 95, and the two stretches that swallow the most bike time are flat.
The second is the swim exit. A kilometre of running separates the water from the Seafront Car Park, the zig zag ramp is part of it, and an athlete who has practised nothing but swimming arrives in transition already in trouble. It is the cheapest leg of the day to get right.
The third is kit. The organiser logged a low of 12 C and a high of 22 C on the same day in 2024, with the water at 17 C. What you pull on at sunrise in the Seafront Car Park is what you carry through the warmest hours of the afternoon.
Conditions on the day
- 2025high 18 C, low 16 Cwater 17 C
- 2024high 22 C, low 12 Cwater 17 C
From the organiser’s own records. Not a forecast.
Every session is a claim, every block is a test
A plan is not a calendar. Each key session states what it trains and how that is checked, and each block ends with a public verdict before the next one is chosen.
What a block promises
Swim muscular endurance moves from your baseline to a stated target by the end of Foundation 2
- The baseline is your measured score when the block starts. The target is the score the model predicts for it.
- Verified at the block’s recovery week, by a field test or a refresh of the supply read from your history.
- Confidence rises by agreement between independent signals, never by one metric crossing a line.
- A block that misses its target is a public miss. The next block is chosen from what was proven, not from what was planned.
- 01Stimulus achievedThe work landed in the zone the session named, for the dose it named.
- 02Partially achievedSome of the work landed. The session banks what it can prove.
- 03Not achievedThe load may have been there. The stimulus was not, so nothing is banked.
- 04Data insufficientNo usable stream. The session is neither credited nor blamed.
- Session verified
- Progression banked
- Block verified
- Priority reassessed
- Plan adapted
Your numbers, this course
Analyze IRONMAN Wales against my fitness
The same simulation and the same Focus Lab read, on your thresholds instead of a band’s. Three numbers give a finish estimate and a partial read. A connected history gives the whole table.
The first 14 days are free.
- Trained band finish
- 12:33:38
- Of the day on the bike
- 54%
- Dimensions scored per leg
- 12
- Season runway shown
- 28 wk
Questions people ask
- How hilly is the IRONMAN Wales bike course?
- It climbs 1819 m across 178 km, and the steepest sustained climb in the organiser's own course file is 623 m at 7.7 percent. Most of the bike's time sits on the flat road between the rises rather than on them.
- What water temperature should I expect at Tenby?
- The organiser recorded 17 C in 2025 and 17 C in 2024. The air was the bigger variable, a high of 22 C against a low of 12 C on race day in 2024.
- Is the IRONMAN Wales run course flat?
- No. It climbs 534 m across 42.2 km, which is more metres for every kilometre than the bike course climbs. It runs through the town centre past the medieval town walls, and the zig zag ramp is on it.
- How long should an IRONMAN Wales training plan be?
- The shortest season Nymiva builds for a full-distance triathlon is 28 weeks, and the plan on this page uses that runway with 3 developmental blocks. A bigger goal makes a season longer, never shorter.
Course data from the organiser’s published files, analysed 23 Sept 2026 by engine 1, demand model 4. Reference times are simulated for a peer band at a stated reference athlete and are not a prediction for anyone. Nothing on this page is medical advice.
IRONMAN® and IRONMAN 70.3® are registered trademarks of World Triathlon Corporation. Nymiva is an independent training platform and is not affiliated with, sponsored by or endorsed by World Triathlon Corporation. Course data is read from the organiser’s public course pages for the purpose of describing the event.