The Grand Colombier, the highest point of the Bugey massif at 1,501 m, has built a formidable reputation among cyclists well beyond the Lyon region: the Culoz side is widely considered one of the hardest climbs in France, with sections that rival Europe’s most extreme passes.
The profile from Culoz
From Culoz, it’s 18.4 km for 1,255 m of climbing, averaging 7.1% — a figure that masks a much harsher reality on the middle section. The Combe du Sires, roughly between kilometre 6 and 10, strings together double-digit gradients almost without a break, with pitches reported above 20% on the steepest stretches.
The scenery, densely forested for the first half, gradually opens onto pasture with a spectacular view of Lac du Bourget and the Alps in the background during the final part of the climb.
How to approach the ride
This climb doesn’t forgive sloppy effort management: going out too hard in the first kilometres, before the Combe du Sires, all but guarantees walking on the steepest sections. A very light gear (an 11-34 cassette or wider, even a 34-tooth compact chainring) isn’t a luxury on this climb, even for experienced climbers.
Heat can be a real factor in summer, with the forested first section offering little airflow; carry a generous water reserve, as refill points are scarce on this side.
When to climb it
The road is generally rideable from May to October, with a risk of residual snow early in the season on the final stretch. The ideal window runs from June to September, ideally avoiding the hottest hours of the day on this climb, which is particularly exposed to full sun on its middle section.
Good to know
Culoz, a small town on the Rhône served by train (Lyon-Geneva line), offers a modest but functional choice of accommodation; the more touristy resorts around Lac du Bourget, about twenty minutes away, make for a more comfortable base for extending the stay.
