Col de Stagn

Overview

Col de Stagn is a hors catégorie climb that hides nothing. Over 9.5 km the road drags you from 1233 m at the base to 2257 m at the summit, an average gradient of 10.83% that almost never lets up. That number alone puts it among the hardest sustained climbs a rider can attempt — most HC efforts settle around 7 or 8 percent, and Stagn sits well above that for its entire length. The net elevation gain is 1024 m, with a total ascent of 979 m once the small undulations are accounted for. There is no easy way to describe a wall this long: it is simply a climb you survive rather than one you attack.

How the Gradient Unfolds

The defining feature of Col de Stagn is not the average but the spikes. With a maximum gradient of 34.51%, the climb contains pitches steep enough to force even strong riders out of the saddle and into a grinding, wrestling rhythm. Because the average is already 10.83%, those maximum ramps are stacked on top of terrain that offers no recovery. Expect the gradient to hover in the low teens through much of the middle, then rear up toward that 34.51% figure on its cruellest sections. The last stretch toward 2257 m is where thin air compounds the pitch, and the 1024 m of accumulated gain sits heavy in the legs.

Pacing Notes

On a climb this relentless, pacing is everything. The single biggest mistake is treating the opening kilometres like the rest of the road — with an average of 10.83% there is no flat to hide on, so your effort must be metered from the first pedal stroke. Ride to your FTP and hold a steady, sustainable power rather than surging into the ramps. On the steepest pitches approaching 34.51% you will inevitably spike well above threshold, so bank patience on the shallower sections to absorb those costs. If you are unsure of your threshold, run the numbers through the FTP estimator before you commit to a target, then build a plan that keeps you below the red across all 9.5 km.

Gearing

Do not under-gear this climb. With a 10.83% average and ramps hitting 34.51%, most riders will want the lowest ratio they can bolt on. A compact 34-tooth chainring paired with a 34×32 cassette is the sensible floor for strong climbers, but on pitches this steep a 34×34 gives you the extra margin to keep the cranks turning instead of stalling. Given the full 9.5 km at double-digit gradients and 1024 m of climbing, err toward the easier option: spinning a 34×34 up the worst of it will always beat grinding a 34×32 to a standstill.

Summary

Col de Stagn earns its HC rating without argument. It is short enough to memorise and steep enough to remember — 9.5 km, 10.83% on average, and a savage 34.51% at its worst, carrying you from 1233 m to 2257 m. Gear low, pace with discipline, and respect every metre of the 1024 m gain.

Length: 9.5 km
Average gradient: 10.83%
Max gradient: 34.51%
Start: 1233 m
Summit: 2257 m
Net gain: 1024 m
Total ascent: 979 m
Category: HC