Col des Lacs Noirs

Overview

The Col des Lacs Noirs is a genuine hors catégorie test, and the numbers explain why. At 29.4 km long it is the kind of climb you settle into rather than attack, and over that distance it averages 6.23% — a gradient that never lets you coast but never quite crushes you either. From a start elevation of 600 m the road works its way up to a summit at 2428 m, delivering 1828 m of net elevation gain. That is a full mountain's worth of vertical, sustained for the better part of an hour or more for most riders.

How the Gradient Unfolds

A 6.23% average across 29.4 km sounds even, but the total ascent tells a subtler story. The climb accumulates 1867 m of total ascent against 1828 m of net gain, meaning the road is not perfectly monotonic — there are small dips and flatter shelves where you briefly give back a little height before clawing it back. Those 39 m of "extra" climbing hidden inside the profile are where rhythm is either found or lost. Expect the grade to breathe: ramps that push above the average, then reprieves that tempt you to surge. On a climb this long, resisting that temptation is the whole game. The upper reaches, thinning toward 2428 m, are where the sustained effort and altitude combine to make even moderate percentages feel steeper than the sign says.

Pacing Notes

This is a climb ridden by the numbers, not by feel. With nearly 1828 m to gain, going into the red early is punished ruthlessly over the remaining kilometres. Anchor your effort to your FTP: on a full-length HC ascent like this, most riders will want to sit comfortably below threshold and hold it steady rather than chase the ramps. Treat every steeper section as a place to hold power, not add it, and let the flatter shelves recover you rather than accelerate you. If you are unsure of your current threshold, run the FTP estimator before you set your target — a climb of 29.4 km leaves no room for a guessed number. Fuel and drink from the bottom; the summit at 2428 m is a long way from the 600 m start.

Gearing

At 6.23% average over 29.4 km, gearing is about protecting your legs for the full 1828 m of climbing, not just surviving one steep pitch. A compact 34-tooth inner ring is the sensible front choice. Pair it with a wide-range cassette: a 34×32 gives most fit riders a manageable low gear for the sustained middle sections, while a 34×34 buys extra insurance for the thinner air near the 2428 m summit and for the ramps that sit above the average. If in doubt on an HC climb this long, size down — spinning a slightly easier gear preserves the muscular reserves you will need in the final kilometres.

Summary

The Col des Lacs Noirs is a patient rider's climb: long, steady and unrelenting, rewarding disciplined pacing and honest gearing over bravado. Respect the 29.4 km, meter your effort, and the 2428 m summit is well within reach.

Length: 29.4 km
Average gradient: 6.23%
Max gradient: n/a
Start: 600 m
Summit: 2428 m
Net gain: 1828 m
Total ascent: 1867 m
Category: HC