Race Day in Thun: Timeline, Common Mistakes, and Plan Bs

The Days Before

In 2023 the schedule had registration on Friday and bike check-in on Saturday (2027 times to be confirmed on the official website). Two priorities on those days:

• Swim in the lake. Water averages around 17 °C, with reports between 15 and 18 °C. If you don't have cold-water experience, the first few minutes of the race can cost you: do at least one adaptation swim in the days before and decide then whether to use a neoprene cap.
• Walk the transition area. T1 and T2 are at the Lachen stadium, with roughly 300 m from the swim exit and about half a kilometer of running to the bags. Memorize everything.

Race Morning

The start is from the beach, with a rolling start in corrals seeded by predicted swim time (2024 format). Line up in the honest corral for your level: race reports flag crowding and light chop in the final section of the swim, and starting too far forward means getting swum over.

A precedent worth knowing: in 2024 the start was briefly delayed due to morning fog. Build it into your plan: breakfast and pre-race gel timing need to handle a 30-60 minute delay without wrecking you. Bring something extra to snack on.

Because of that same fog and the limited visibility in the water noted in race reports: goggles with clear or lightly mirrored lenses, not dark ones.

How the Day Unfolds

• Swim (early hours): cold, clear water, variable visibility. A 2023 report measured roughly 4,150 m, ~350 m over the official distance: don't let your GPS demoralize you—swim buoy to buoy. Then 300 m of running to T1, no sprinting.
• Bike (morning and midday): you start cool, but the second lap falls in the hot hours. In 2023 some sections hit 36 °C. The two 20-25 minute climbs at 4-5% per lap need to be ridden at a capped effort; the final ~8 km of descent on each lap are for eating, drinking, and bringing your heart rate down.
• Marathon (afternoon): three flat laps through the town center, but on mixed surfaces with gravel and cobbles. Aid stations offer ice, cold showers, Coke, and broth: use them with a plan, not on instinct.

Common Mistakes, Already Documented

Race reports on this event describe recurring mistakes:

1. Running the 300 m after the swim hard. Long-transition anxiety, wasted energy. 2. Hammering the climbs on the first bike lap. The bill comes due on lap two, in the heat. 3. Recovering on the descents. Very fast descents and a no-aero zone: the margin for error is minimal. 4. Treating aid stations like a buffet. One report mentions cramps from overdoing it: three laps multiply the chances to get it wrong.

Plan Bs to Have Ready

• Start delayed by fog: flexible pre-race nutrition, warm layer kept on until the last moment.
• Extreme heat scenario: increased hydration and sodium plan for the second bike lap, ice and cold-shower protocol every run lap, marathon pace revised downward.
• Colder water than expected (15-16 °C): neoprene cap in your bag, dry-land warm-up, controlled breathing in the first few minutes.
• Swim that measures long: ignore the watch, sight clean.

The Final Rule

In Thun the day is long and changes character three times: cold in the water, potentially scorching on the bike, grinding on the run's mixed surfaces. Those who arrive with a plan for every scenario—and the discipline not to overdo it in the first four hours—get to race the marathon this flat course promises. Check cutoff times and updated rules in the 2027 athlete guide: they're not available from the sources consulted.