Col des Chalettes

Overview

The Col des Chalettes is a genuine hors catégorie (HC) test — the hardest rung on the climbing ladder, above categories 1 through 4. Over 21.4 km it hauls you from a valley floor at 414 m to a summit of 1903 m, a net gain of 1489 m at an average gradient of 6.95%. That average alone would make for a hard hour of climbing, but the headline number is the 27.85% max — a wall steep enough to force even strong riders out of the saddle and into survival mode. With 1556 m of total ascent packed into the profile, this is a climb that rewards patience and punishes ego.

How the Gradient Unfolds

An average of 6.95% across 21.4 km never tells the full story, and the gap between that figure and the 27.85% max is the whole point here. A climb this long that still hides a near-28% pitch is not evenly graded — it stacks its difficulty into ramps. Expect long stretches that sit around or just under the 6.95% mean, interrupted by sharper kicks where the road rears up well into the teens and beyond. The difference between the 1556 m of total ascent and the 1489 m of net gain is small, which tells you the road climbs almost relentlessly upward with little relief — there is barely any descending to recover on. Treat every shallow section as a chance to breathe before the next ramp.

Pacing Notes

On a climb of 21.4 km, pacing is everything. Riding at or just below your FTP for the bulk of the ascent is the sustainable play — but the 27.85% max means you cannot pace purely on power. On the steepest ramps your cadence will collapse and your power will spike no matter how disciplined you are, so build a buffer everywhere else. Start conservatively: the summit sits at 1903 m and the finish is a long way from the 414 m base, so a hot opening third will cost you dearly over the final kilometres. If you do not know your threshold, plug your numbers into the FTP estimator before you commit to a target, then aim to keep the steady sections a touch under that figure so the walls do not blow you apart.

Gearing

For an HC climb averaging 6.95% with a 27.85% max, gear low and gear again. A compact 34-tooth chainring paired with a 34×32 cassette is the sensible baseline for strong climbers, giving you a bailout ratio that keeps the pedals turning on the steady sections. But given that near-28% wall, most riders will be far happier on a 34×34 — the extra sprocket buys precious cadence when the road stands up and 1489 m of accumulated fatigue is already in your legs. If your frame and derailleur allow anything lower still, this is the climb to use it. Spinning a low gear beats grinding to a halt.

Summary

The Col des Chalettes earns its HC label honestly: long, steep, and unforgiving, with a 27.85% sting hidden inside its 21.4 km. Pace it with respect, gear it low, and let the numbers do the intimidating for you.

Length: 21.4 km
Average gradient: 6.95%
Max gradient: 27.85%
Start: 414 m
Summit: 1903 m
Net gain: 1489 m
Total ascent: 1556 m
Category: HC