Col du Tsan

Overview

The Col du Tsan is a monster of an ascent: 26.5 km of near-continuous climbing that lifts you from a start elevation of 470 m all the way to a summit at 2316 m. That is a net elevation gain of 1846 m, with a total ascent of 1803 m once you account for the handful of brief respites along the way. At an average gradient of 6.97% sustained across such distance, it earns its HC (hors catégorie) rating — the hardest classification there is, sitting above categories 1 through 4. This is a climb measured not in minutes but in hours of sustained effort.

How the Gradient Unfolds

Do not be lulled by the 6.97% average. An average is a story of extremes, and here the extremes are severe: the road bites up to a maximum of 20.83% at its steepest. That is a ramp more than twice the average, the kind of pitch that forces you out of the saddle and empties your legs if you hit it carelessly. The difference between the summit at 2316 m and the start at 470 m is 1846 m of vertical to be earned, and the gap between net gain (1846 m) and total ascent (1803 m) tells you the climb is almost entirely upward — there are no meaningful descents to recover on. Expect the gradient to swing between merely hard and genuinely savage across all 26.5 km.

Pacing Notes

On a climb this long, pacing is everything. Your goal is to hold a sustainable percentage of your FTP rather than chasing the steep ramps — every match you burn on a 20.83% pitch is one you will miss over the remaining kilometres. Ride the average, spin the steep sections, and treat the whole 26.5 km as a single controlled effort. If you are unsure what wattage you can hold for the better part of an hour or more, run the numbers first with the FTP estimator and set a ceiling you will not exceed early. Discipline in the opening kilometres buys you the legs to survive the last of the 1846 m.

Gearing

For an HC climb averaging 6.97% and spiking to 20.83%, gear low and gear generously. A compact 34-tooth chainring paired with a wide-range cassette is the sensible baseline. A 34×32 will get most fit riders up the steadier stretches, but on the steepest ramps you will be grateful for a 34×34 to keep your cadence alive without grinding to a stall. Given 1803 m of total ascent, prioritise the ability to spin over the ability to push a big gear — protect your knees and your matches over the full 26.5 km.

Summary

The Col du Tsan is a true HC test: long, relentless, and unforgiving on the steepest pitches. Respect the distance, pace off your FTP, and carry enough gear to keep spinning to the 2316 m summit.

Length: 26.5 km
Average gradient: 6.97%
Max gradient: 20.83%
Start: 470 m
Summit: 2316 m
Net gain: 1846 m
Total ascent: 1803 m
Category: HC