Les Clayes-sous-Bois - 21km 2026
Forecast published: 36°F feels-like at the coldest, 43°F at the warmest, no notable rain.
Here you'll find the elevation profile and an estimated finish time based on your UTMB Index.
What's your time based on your UTMB?
Times estimated by the RAVIT model, learned from real ultra-trail finish times. Enter your UTMB Index (utmb.world) to get a personalized estimate.
Cut-off times and crew - Les Clayes-sous-Bois - 21km · 2026
| Aid station | Cum. km | Cum. D+ | Seg. km | Seg. D+ | Seg. D- | Crew | Cut-off | Access |
|---|---|---|---|---|---|---|---|---|
| Arrivée | 21.2 | 307 m | 21.2 | 307 m | 313 m | — | — | — |
Data from the official race rules, checked for every edition. The race rules prevail. Positions are interpolated along the GPX track and are a guide, not official course marking.
What you'll find at each aid station
Aid station contents not documented.
Elevation profile
The course and its aid stations
Les Clayes-sous-Bois - 21km: times, aid-station stops and fuelling needs by UTMB® Index
Between a UTMB® Index of 500 and 800, the estimated finish time on this race runs from 2h07 to 1h26, and the aid-station stop budget from 0h02 to 0h01. The longer the race, the more stops weigh: this is time you should plan to spend standing still, not only running.
Source
| UTMB® Index | Estimated time | Of which stops | Night hours | Carbs | Fluid | Sodium |
|---|---|---|---|---|---|---|
| 500 | 2h07 | 0h02 | — | 127 g | 1.5 L | 1,060 mg |
| 550 | 1h57 | 0h02 | — | 117 g | 1.4 L | 977 mg |
| 600 | 1h50 | 0h02 | — | 110 g | 1.3 L | 917 mg |
| 650 | 1h43 | 0h01 | — | 103 g | 1.2 L | 860 mg |
| 700 | 1h37 | 0h01 | — | 97 g | 1.1 L | 805 mg |
| 750 | 1h31 | 0h01 | — | 91 g | 1.1 L | 759 mg |
| 800 | 1h26 | 0h01 | — | 86 g | 1 L | 713 mg |
Figures based on 60 g of carbohydrate, 700 mL of fluid and 500 mg of sodium per hour, "average" preparation and mild conditions (15–25 °C). Above 25 °C, count on roughly 900 mL/h and 700 mg/h. Carbohydrate intake is trained: 60 g/h is a floor, 90 g/h assumes a glucose-fructose blend and a gut used to it.
Other trails worth preparing for
- Saint Eusèbe - Trail du Four à Pain15 km · 539 m D+ · October 31, 2026
- Valbonne - 15km-night15 km · 400 m D+ · October 31, 2026
- COTTANCE - 20km-night20 km · 750 m D+ · October 31, 2026
- Orgères - Trail découverte - 15km nocturne14 km · 169 m D+ · October 31, 2026
- Volvic - 16km-night17 km · 648 m D+ · October 31, 2026
- Bouaye - La Lanterne24 km · 190 m D+ · October 31, 2026
- Saint Eusèbe - Trail Panoramic27 km · 956 m D+ · October 31, 2026
- Courzieu - 25km-night25 km · 1,160 m D+ · October 31, 2026
- Estialescq - 19km19 km · 550 m D+ · October 31, 2026
Sources and method
- Time projection — times by UTMB Index are taken from the actual splits of runners in each level band on previous editions of this race, aid station stops included. No formula is used as long as these results exist.
- Trail nutrition — hourly targets for carbohydrate, fluid and sodium follow the commonly accepted ultra-endurance guidance. La Clinique du Coureur — Fuelling in trail running
- Course, aid stations and cut-offs — taken from the event's official rules, which prevail in case of any discrepancy. Official site — Les Clayes-sous-Bois - 21km
Weather for Les Clayes-sous-Bois - 21km
Section-by-section forecasts for Les Clayes-sous-Bois - 21km, calculated at the estimated passing time: feels-like temperature, rain or snow, wind and thunderstorms. Three models — AROME (Météo-France), ICON (DWD) and ECMWF IFS — served from the finest to the farthest-reaching.
Forecasts for a 600 UTMB Index runner, at their estimated passage time. Start Sun, 11/01 09:00 AM: Fog, 41°F. Coldest: 36°F feels-like at Arrivée (Sun, 11/01 10:49 AM); warmest: 43°F at Arrivée (Sun, 11/01 10:49 AM). No notable rain forecast on the course. Gusts up to 15 mph at Arrivée.
Forecast, not guaranteed: in the mountains a model describes a grid of several hundred meters, not the slope you're on.
Weather data: Météo-France (AROME), DWD (ICON), ECMWF (IFS) — CC BY 4.0, via Open-Meteo
Frequently asked questions
How many checkpoints?
Les Clayes-sous-Bois - 21km has 1 checkpoint: 1 checkpoint with undocumented contents. Details are in the two tables above.
What distance and elevation gain?
Les Clayes-sous-Bois - 21km is 21 km long with 307 m of elevation gain.
How long to finish?
With a UTMB Index of 600 (average runner), the estimated time is around 1h50 for Les Clayes-sous-Bois - 21km.
What's the weather forecast?
Forecast published: 36°F feels-like at the coldest, 43°F at the warmest, no notable rain. RAVIT publishes the weather for Les Clayes-sous-Bois - 21km section by section: feels-like temperature, rain or snow, wind and storms, at the estimated passage time. Forecasts come from AROME (Météo-France), ICON (DWD) and ECMWF IFS, refreshed several times a day.
Want to stack the odds in your favor for Les Clayes-sous-Bois - 21km?
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