Col de Bassachaux

Overview

Col de Bassachaux is a genuine hors catégorie test, and the numbers make no apology for it. From a start at 415 m it runs 21.8 km to a summit of 1909 m, stacking up 1494 m of net elevation gain along the way. The total ascent of 1551 m tells you the road is not a clean, one-way climb — there are 57 m of give-back somewhere in the profile, small dips and false flats that briefly hand elevation back before the road claws it away again. At 6.85% average over that full distance, this is a climb that rewards patience and punishes anyone who treats the opening kilometres as a warm-up.

How the Gradient Unfolds

The headline average of 6.85% is honest but incomplete. The defining feature is a max gradient of 29.09% — a wall so steep it dwarfs the average nearly four and a half times over. A pitch like that cannot be spun through casually; it forces you out of the saddle or off the bike. Because the mean sits at 6.85% while a 29.09% ramp exists, long stretches must run gentler than the average to balance the arithmetic. Expect the climb to breathe: sustained mid-single-digit grinding, punctuated by sharper kicks, with that one signature ramp waiting to break your rhythm. Over 21.8 km, those swings add up — and the 1551 m of total ascent versus 1494 m net confirms the road never lets you fully settle.

Pacing Notes

On a climb this long, discipline beats bravado. Your FTP is the anchor: hold a steady sub-threshold effort across the shallower kilometres and bank energy for the 29.09% wall, which will spike your power far above sustainable output no matter how well you pace. If you do not know your threshold, run the numbers through the FTP estimator before you commit to a target. With 1494 m of climbing to distribute, going 10% too hard in the first third of the 21.8 km will cost you dearly by the summit at 1909 m. Ride the average, respect the ramp, and keep something in reserve for the elevation that lingers near the top.

Gearing

Do not underestimate the gearing demands here. The 29.09% max gradient alone justifies your easiest possible setup, and 21.8 km of accumulated fatigue makes low ratios even more valuable late on. A compact 34-tooth chainring paired with a wide cassette is the sensible baseline. Run at least a 34×32 if your legs and terrain knowledge are strong, but for most riders a 34×34 is the smarter call — that extra sprocket buys cadence and saves your knees when the 6.85% average stacks onto the steep pitches. On an HC climb gaining 1494 m, gearing you never need beats gearing you desperately wish you had.

Summary

Col de Bassachaux is a full-value hors catégorie ascent: long at 21.8 km, relentless at 6.85% average, and genuinely dangerous at 29.09% max. With 1494 m of net gain to a 1909 m summit, it demands smart pacing and generous gearing from the first pedal stroke.

Length: 21.8 km
Average gradient: 6.85%
Max gradient: 29.09%
Start: 415 m
Summit: 1909 m
Net gain: 1494 m
Total ascent: 1551 m
Category: HC