Baisse de Sanson / Bassa di Sanson

Overview

The Baisse de Sanson, also signed as the Bassa di Sanson, is a genuine hors catégorie test that asks a serious question of every rider who lines up at its base. Over 19.6 km the road climbs from 285 m to a summit of 1954 m, delivering 1669 m of net elevation gain at a relentless 8.51% average gradient. The total ascent recorded on the profile is 1633 m, meaning almost every metre of this climb is spent going up — there is precious little respite once the road tilts skyward. With a maximum pitch of 13.59%, the Sanson combines sustained difficulty with sharp punches, earning its HC rating honestly.

How the Gradient Unfolds

An 8.51% average across 19.6 km is the headline, but averages hide the texture. The climb's defining feature is consistency: with only 1633 m of total ascent against 1669 m of net gain, there are effectively no descents to break the rhythm — the road simply keeps rising. That makes the 8.51% figure feel honest rather than diluted by flat sections. The steepest ramps bite at 13.59%, roughly five points above the average, so expect the gradient to swing between hard and very hard rather than easy and steep. Riders should brace for long stretches at or above the mean, punctuated by pitches into the low teens that force a change of cadence or a lift out of the saddle.

Pacing Notes

On a climb this long and this steep, discipline beats bravado. A useful rule of thumb is to hold the lower two-thirds well under your threshold, because 19.6 km at 8.51% will punish any early effort spent above your FTP. If you don't know your current number, run it through the FTP estimator before you plan your target power. Aim to arrive at the mid-point still able to accelerate, then meter your remaining reserves against the 13.59% ramps rather than the average. Because there is no coasting to recover — remember, net gain and total ascent are almost identical — you cannot bank rest, so smoothness of output matters more here than on a rolling climb.

Gearing

For an HC ascent averaging 8.51% over nearly 20 km, gear low and gear early. A compact 34-tooth inner chainring paired with a 34×32 will get most fit riders up the sustained sections, but on the 13.59% ramps a 34×32 can leave you grinding at an unsustainable cadence late in the climb. Fitting a 34×34 buys you a small but meaningful cushion, letting you spin those steepest pitches instead of muscling them. Given the 1669 m of net gain, the extra range of a 34×34 is cheap insurance — you will never regret having one more easy gear on a climb this long.

Summary

The Baisse de Sanson is a big-mountain HC climb that rewards patience, honest pacing, and generous gearing. Long, steep, and almost entirely uphill from base to summit, it is a benchmark day out for any climber.

Length: 19.6 km
Average gradient: 8.51%
Max gradient: 13.59%
Start: 285 m
Summit: 1954 m
Net gain: 1669 m
Total ascent: 1633 m
Category: HC