Col des Chambres

Overview

The Col des Chambres is one of the uncompromising ones. Over 15.3 kilometres it climbs from a valley floor at 670 metres to a summit of 2132 metres, and it does so at an average gradient of 9.53%. That average is the headline: most hors catégorie climbs earn their rank through length or altitude, but Chambres earns it through relentless steepness. There is no gentle valley run-in baked into that figure — nearly the entire road tilts up hard.

The net elevation gain is 1462 metres, while the total ascent logged is 1561 metres. The gap between the two tells you the road is not perfectly monotonic: there are short pitches of false flat or brief dips that you then have to re-climb, adding 99 metres of extra vertical on top of the pure gain. On a climb this steep, every one of those recovered metres is felt.

Classified HC — hors catégorie, the hardest tier, sitting above categories 1, 2, 3 and 4 — this is a climb you plan a whole day around.

How the Gradient Unfolds

With no max-gradient figure recorded, the shape is best read through the average. At 9.53% sustained across 15.3 km, the maths is unforgiving: this is not a climb with a token steep ramp and long recovery. Averaging that number over more than fifteen kilometres means long stretches sit at or near double digits, and the recovery sections are shallow rather than restful.

The 99-metre difference between the 1462 m net gain and the 1561 m total ascent points to a road that undulates within its overall rise — you crest a rise, give a little back, and climb it again. Mentally, treat the whole thing as one long effort at threshold-plus, not a series of distinct sectors. There is no summit-approach easing to bank on; the average holds because the top stays steep.

Pacing Notes

Steepness this consistent rewards discipline over ambition. Pin your effort to your sustainable power for the full 15.3 km, not to how you feel in the first two. A good anchor is your FTP: on an HC climb of this length, riding just under threshold from the base is far safer than surging and blowing up on the upper slopes, where 9.53% offers nowhere to soft-pedal and recover.

If you do not know your number, run it through the FTP estimator before you go — a realistic target watts figure is worth more here than any local knowledge. Aim to arrive at the 2132 m summit tired but intact, not cracked with kilometres still to climb.

Gearing

Gear for survival, not pride. At 9.53% average over 15.3 km, most riders want more range than a standard road setup offers. A compact chainring paired with a wide cassette is the sensible floor: a 34×32 will get many riders up, but on a climb this steep and this long, a 34×34 gives you the extra breathing room to hold a spinning cadence rather than grinding. If your frame and derailleur clear it, err toward the larger sprocket — you will not regret the easier gear on the upper slopes.

Summary

The Col des Chambres is a pure test of sustained steepness: 15.3 km that averages 9.53% and lifts you from 670 m to 2132 m. With 1462 m of net gain and 1561 m of total ascent, its HC classification is fully earned. Pace to your threshold, gear generously, and respect the average — it does not lie.

Length: 15.3 km
Average gradient: 9.53%
Max gradient: n/a
Start: 670 m
Summit: 2132 m
Net gain: 1462 m
Total ascent: 1561 m
Category: HC