From Bourg-Saint-Maurice (2,654 ft / 809 m) to the Col de l’Iseran (9,068 ft / 2,764 m) it’s 29.8 miles (48 km) and 6,414 ft (1,955 m) of elevation difference, at an average of 4.1%. It’s the highest paved pass in the Alps, on the Route des Grandes Alpes, and it’s less a climb than a full day of climbing.
What the climb is like
- Bourg-Saint-Maurice to Sainte-Foy (about 6.2 miles / 10 km). Up the Isère valley at 1-3% with the odd kicker. Good for riding in a group.
- Sainte-Foy to the Tignes dam (about 8.1 miles / 13 km). The road gets harder (5-8%) through La Thuile and Les Brévières, with tunnels and avalanche galleries. Watch the lighting: bring a rear light.
- Lac du Chevril to Val-d’Isère (about 5 miles / 8 km). An almost flat section, with some downhill, along the reservoir. You lose a bit of height here.
- Val-d’Isère to the top (9.3 miles / 15 km at 6%). The real climb: 2,936 ft (895 m) of steady climbing between 5 and 8%, with the odd 10% spike in the last kilometer.
A note on the numbers
Wikipedia and cols-cyclisme give 29.8 miles (48 km) and 6,414 ft (1,955 m) (4.1%). CyclingCols measures 29.1 miles (46.8 km), and Climbfinder 29.5 miles (47.4 km) with 6,726 ft (2,050 m) of total climbing, because it adds the rises after the dips along the lake. We use the elevation difference.
History
The Tour de France first climbed it in 1938: Félicien Vervaecke was first over the top and Gino Bartali caught him on the descent. In 2019, stage 19 was neutralized shortly after the summit because of a hailstorm and a landslide on the descent toward Tignes; Egan Bernal, who had been first over the Iseran, took the yellow jersey and won the Tour.
When to go, water and traffic
It’s only open in summer; outside those months snow closes it. It can be cold at the top even when it’s 86 °F (30 °C) down in the valley: bring a jacket. There’s water and shops in Sainte-Foy, at the Tignes junction and in Val-d’Isère; at the summit, a bar and a chapel. Traffic is heavy in August, with lots of motorcycles.
What gearing to use
The grade is never extreme: a 34x28 is enough for almost everyone. At 3 W/kg and 159 lb (72 kg), you’ll ride about 8.7 mph (14 km/h) on 6% (about 91 rpm in a 34x28) and 6.8 mph (11 km/h) on 8%. Fine-tune your combinations in the gear calculator.
Frequently asked questions
How long does it take to climb the Iseran from Bourg-Saint-Maurice?
A 159 lb (72 kg) rider on a 21 lb (9.5 kg) bike takes about 2 h 37 min at 3 W/kg (216 W), 3 h 02 min at 2.5 W/kg and 2 h 06 min at 4 W/kg, not counting stops. The altitude near the top will cost you some power.
What is the hardest part of the Iseran?
The 9.3 miles (15 km) from Val-d'Isère: 2,936 ft (895 m) of climbing at a steady 6%, with a few sections of 8-10% above 8,200 ft (2,500 m).
When is the Col de l'Iseran open?
Only in summer. In winter the road lies within the Val-d'Isère ski area and can't be crossed.
Can you climb it from the south?
Yes, from Lanslebourg: 20.4 miles (32.9 km) and 4,498 ft (1,371 m) at 4.2%, with a final 8.3 miles (13.4 km) at 7.3% from Bonneval-sur-Arc, harder than the north side.