Alto de Sion

Overview

Alto de Sion is an hors catégorie climb, the hardest classification on the books, and its profile leaves no doubt why. Over 14.4 km the road lifts you from 704 m at the base to a summit of 1823 m, a net gain of 1119 m. The average gradient sits at a punishing 7.78%, and unlike gentler HC climbs that hide easy kilometres, this one keeps the pressure on from bottom to top. With a max pitch of 11.28%, there are moments where the road rears up and forces a decision: hold your rhythm or bleed matches you may need later.

How the Gradient Unfolds

The headline number is the 7.78% average, but averages flatten the story. Total ascent across the climb is 1103 m, only 16 m shy of the net gain of 1119 m — which tells you something important: there is almost no descending or false-flat relief. The road climbs, and keeps climbing, nearly the entire way. That makes Alto de Sion relentlessly consistent rather than explosive. The gradient hovers close to its average for long stretches, then stiffens toward the 11.28% max on the steepest ramps. Because there are so few flat sections to recover, every hard pitch chips away at your reserves, and the effort compounds the higher you go.

Pacing Notes

On a climb this sustained, discipline beats bravado. The distance from 704 m to 1823 m is covered at an average of 7.78%, so your best result comes from settling into an effort you can hold for the full 14.4 km rather than surging on every ramp. A good target is riding just below your FTP on the average gradient, leaving headroom for the 11.28% pitches where power naturally spikes. If you do not know your threshold, run the numbers through the FTP estimator before you commit to a pace. Because the climb barely lets up — total ascent nearly matches net gain — there is no coasting section to bail you out if you go too deep early. Start conservatively; you can always lift the pace in the final kilometres.

Gearing

With 1119 m of net climbing at 7.78% and ramps touching 11.28%, gearing is not the place to save weight or ego. For most riders a compact 34-tooth chainring paired with a wide-range cassette is the right call. A 34×32 will get many trained riders up at a workable cadence, but on a sustained HC effort where the road rarely eases, a 34×34 gives you the extra margin to keep your legs spinning rather than grinding to a stall on the steepest sections. If you are between the two, err toward the easier ratio — protecting your cadence over 14.4 km pays off long before the summit.

Summary

Alto de Sion is a true HC climb: long, steep, and almost entirely without relief. From 704 m to 1823 m it demands patience, honest pacing, and gearing that respects the gradient. Ride it smart and the summit is a reward; ride it recklessly and the 11.28% ramps will collect their debt.

Length: 14.4 km
Average gradient: 7.78%
Max gradient: 11.28%
Start: 704 m
Summit: 1823 m
Net gain: 1119 m
Total ascent: 1103 m
Category: HC