Forcella la Sidon bassa

Overview

Forcella la Sidon bassa is a hors catégorie (HC) climb, the hardest rung on the classification ladder, and it earns the label the honest way: with length. At 23.2 km it is a genuine mountain haul, starting at 521 m and topping out at 2063 m. The net elevation gain is 1542 m, while the total ascent measured along the road is 1487 m — the small gap tells you the climb is not relentlessly upward but carries a few flatter or momentarily easing passages between its harder stretches. The average gradient of 6.63% sounds civil, and for long portions it is. What makes this an HC ascent is the combination of that sustained pitch, the sheer distance, and the thin air waiting near the 2063 m summit.

How the Gradient Unfolds

The headline number is the 32.75% max gradient — a wall far steeper than the 6.63% average and a reminder that averages hide the sharpest teeth. Over 23.2 km an average of 6.63% means the effort is broadly steady, but the spread between 6.63% and 32.75% is enormous. Expect the road to breathe: ramps that spike well into the double digits, then sections that fall back toward or below the mean, letting you recover a little before the next kick. With 1542 m of net gain and only 1487 m of measured ascent, the profile is almost entirely climbing, so there is little true rest — the easier metres are relative, not flat. Treat the steepest ramp as an event to survive rather than attack.

Pacing Notes

On a climb this long, discipline beats bravado. Anchor your effort to your FTP and aim to hold a sustainable percentage of it for the full 23.2 km rather than burning matches early. The steepest ramps toward 32.75% will briefly push you above threshold whether you like it or not, so bank nothing before them — arrive with headroom. If you do not know your threshold, estimate it first with the FTP estimator, then set a target power you can defend from 521 m all the way to 2063 m. Remember that the final kilometres sit near the 2063 m summit, where thinner air quietly trims your output; plan for that fade and keep your first two-thirds conservative.

Gearing

With 23.2 km at 6.63% average and pitches touching 32.75%, gearing is not a place to be brave. A compact 34-tooth front paired with a wide cassette is the sensible baseline. A 34×32 will get most strong riders up the sustained sections, but for the steepest ramps — and for the fatigue that 1542 m of net climbing brings — a 34×34 gives you a genuinely easier bailout to keep your cadence up and your knees intact. If your bike allows an even larger sprocket, take it; spinning a low gear over 23.2 km is far kinder than grinding.

Summary

Forcella la Sidon bassa is a long, honest HC test: steady on average, brutal in its steepest metre, and unforgiving over its full length. Pace to your threshold, gear low, and respect the thin air at the top.

Length: 23.2 km
Average gradient: 6.63%
Max gradient: 32.75%
Start: 521 m
Summit: 2063 m
Net gain: 1542 m
Total ascent: 1487 m
Category: HC