Col de Trepertuis

Overview

The Col de Trepertuis is one of those climbs where the numbers alone tell you almost everything you need to know. Over 17 km the road hauls you from a start elevation of 380 m to a summit of 1877 m, a net gain of 1497 m. That works out to an average gradient of 8.82%, a figure that places it firmly in the hors catégorie bracket — the hardest classification there is, sitting above categories 1, 2, 3 and 4. There is no easing-in, no gentle valley approach hidden in that average: nearly nine percent sustained for the better part of an hour is relentless by any standard.

How the Gradient Unfolds

An 8.82% average is punishing, but the real character of Trepertuis lives in its variation. The maximum gradient reaches 21.16%, roughly two and a half times the average, which means the mean is smoothing over some genuinely savage pitches. Expect the road to swing between steep and steeper rather than steep and forgiving. With a total ascent of 1458 m recorded against a net gain of 1497 m, the profile is almost entirely upward — there is very little false-flat or descent to break the rhythm, so the elevation you lose is negligible. Treat every ramp toward that 21.16% ceiling as a moment to survive rather than attack, and assume the gradient will keep testing you until the final metres near 1877 m.

Pacing Notes

The single most important skill on a climb like this is restraint. At 8.82% for 17 km, going into the red early is unrecoverable, because there is no flat section where you can spin the effort back. Anchor your pacing to your FTP and aim to sit just below threshold on the sustained sections, keeping a small reserve for the pitches that spike toward 21.16%. If you do not know your threshold power, run the numbers through the FTP estimator before you commit to a target. On the steepest ramps your power will naturally surge — let it, briefly, but bring it back down the moment the gradient relents rather than trying to hold a hero pace all the way to 1877 m.

Gearing

Do not under-gear this one. For an HC climb averaging 8.82% with maximums of 21.16%, most riders will want the widest range they can fit. A compact 34-tooth chainring paired with a 34×32 cassette is a sensible baseline for strong climbers, but for the ramps toward 21.16% a 34×34 gives you a meaningfully easier bailout gear and lets you keep cadence up instead of grinding to a standstill. Over 17 km and 1497 m of climbing, the extra range pays for itself many times over in preserved legs.

Summary

The Col de Trepertuis is an uncompromising HC test: 17 km, 8.82% average, spikes to 21.16%, and almost 1500 m of vertical to the summit. Pace with discipline, gear generously, and respect the length as much as the steepness.

Length: 17 km
Average gradient: 8.82%
Max gradient: 21.16%
Start: 380 m
Summit: 1877 m
Net gain: 1497 m
Total ascent: 1458 m
Category: HC