Diagonale des Fous course

Source: The distance and the ascent are from the race organiser (grandraid-reunion.com). We calculate the descent from the organiser ascent and the elevation difference between the start and the finish. The elevation profile and the gradient data come from a 30 m digital elevation model (SRTM). All elevations are to the nearest 10 m (50 ft).

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About the course

The French-centric, Diagonale des Fous ("Madmen's Diagonal") is a c.112 mi180 km point-to-point ultramarathon that crosses the volcanic island of Réunion in the Indian Ocean.

It starts on the south coast at Saint-Pierre, close to sea level, and climbs into the island's mountainous interior across the high plains of the Plaine des Cafres. It then drops into the Cirque de Cilaos, crosses into the remote Cirque de Mafate, and descends to the finish in the capital, Saint-Denis, on the north coast.

The course climbs from the coast to a high point of c.8,250 ft2,510 m and averages around 3,650 ft1,110 m above sea level. It has 33,450 ft10,200 m of elevation gain and 33,300 ft10,150 m of loss. Much of it runs through the Pitons, Cirques and Remparts UNESCO World Heritage Site, on steep, technical trails of volcanic rock, tree roots, ladders and stone steps, across rainforest, high moorland and sheer-sided cirque walls.

The Diagonale des Fous course climbs around 33,450 ft10,200 m and descends around 33,300 ft10,150 m over its c.112 mi180 km distance, starting and finishing close to sea level on the coast. Its total climbing is almost identical to that of the Hardrock 100, and its gain per km is very similar to UTMB.

Ascent & descent analysis

In mid-October, the Diagonale des Fous starts and finishes in warm, tropical coastal conditions, typically around 25°C77°F. In the island's high interior temperatures are far cooler, often dropping below 10°C50°F and occasionally close to freezing near the course high point.

Some rain is likely. Cloud and mist often build over the mountains and cirques, and showers can make the steep volcanic trails wet and slippery.

The weather data has been obtained using the Open-Meteo historical weather API.

Conditions at the start line

The pictograms below show the conditions at the start of the course on the race date in each of the last five years.

Temperature range on course

Temperatures experienced on course are impacted by elevation. The graph below shows the temperature range for the five most recent events at different parts of the course.

Daylight hours

The graph below shows the daylight hours on the day of the 2026 edition (15 October), in local time.

The Diagonale des Fous starts in Saint-Pierre close to sea level and climbs into Réunion's volcanic interior, reaching a high point of around 8,250 ft2,510 m before descending to finish in Saint-Denis on the coast. The altitude is only moderate, but the repeated climbs from near sea level to over 6,550 ft2,000 m mean runners go through big swings in temperature during the race.