Col de Chésery

Overview

Col de Chésery is a hors catégorie monster, and the numbers make the case on their own: 24.1 km of continuous climbing at an average gradient of 6.58%, starting at 411 m and topping out at 1996 m. That is 1585 m of net elevation gain, with a total ascent of 1660 m once you account for the small dips and rollers along the way. As an HC climb — the hardest rung above categories 1 through 4 — this is a full commitment. There is no easing into it and no coasting your way out. Budget an hour or more of sustained effort and treat it as the centerpiece of your ride, not a warm-up for something else.

How the Gradient Unfolds

A 6.58% average across 24.1 km sounds steady, but the max gradient of 28.67% tells you the road is anything but uniform. Expect long stretches near the average punctuated by sharp, punishing ramps that spike far above it. The gap between the 1660 m total ascent and the 1585 m net gain is small, which means there is very little downhill relief — nearly every meter you climb, you keep. Mentally, break the ascent into thirds. Ride the lower slopes conservatively, hold your rhythm through the middle where fatigue accumulates, and save something for the pitches near the summit, where a 28.67% wall can undo a reckless early pace in seconds.

Pacing Notes

On a climb this long, pacing discipline decides everything. Anchor your effort to your FTP and aim to sit just below threshold for the sustained sections, leaving headroom to absorb the steep ramps without redlining. If you do not know your current threshold, run the numbers through the FTP estimator before you attempt it, then set a power or heart-rate ceiling and hold it. The 28.67% max gradient will force brief surges no matter how disciplined you are, so the goal is to keep your average effort controlled everywhere else. Going out too hard on the lower 411 m to 1996 m span is the classic mistake here — the climb is long enough to punish it with real interest.

Gearing

Gear for the steep ramps, not the average. With a 28.67% max gradient over 24.1 km, most riders will want the widest range they can fit. A compact 34-tooth chainring paired with a 34×32 low is a sensible baseline for strong climbers, but on an HC ascent this long, a 34×34 gives you the extra margin to keep the pedals turning smoothly when the road kicks up. If your setup allows an even easier ratio, take it — spinning a low cadence up a wall beats grinding to a stall. The difference between 34×32 and 34×34 is small on paper but decisive when your legs are 1585 m deep.

Summary

Col de Chésery earns its HC rating honestly: long, steep, and unforgiving from 411 m all the way to 1996 m. Pace it by your threshold, gear it for the 28.67% ramps, and respect the full 24.1 km. Do that, and the summit is yours.

Length: 24.1 km
Average gradient: 6.58%
Max gradient: 28.67%
Start: 411 m
Summit: 1996 m
Net gain: 1585 m
Total ascent: 1660 m
Category: HC