Col de Nannaz

Overview

The Col de Nannaz is a full hors catégorie ascent, and its dimensions leave little room for doubt about the effort ahead. Over 28.8 km the road lifts you from a valley floor at 431 m to a summit of 2647 m, a net gain of 2216 m across an average gradient of 7.7%. This is not a climb you drift up. At nearly 29 km long with an HC rating, it belongs to the small family of European ascents that demand hours of sustained climbing rather than minutes of sharp effort. The total ascent of 2205 m confirms the road climbs almost relentlessly, with only marginal respite along the way.

How the Gradient Unfolds

A 7.7% average across 28.8 km sounds steady, but averages hide the story. The presence of a 21.82% maximum gradient tells you the road pitches far above its mean in places — a ramp near 22% is steep enough to force riders out of the saddle and into damage-limitation mode. Expect the climb to breathe: stretches close to the average that let you settle into rhythm, punctuated by sharper walls that spike well into the teens and beyond. Because the net gain (2216 m) sits just above the total ascent (2205 m), the profile is almost monotonically upward — there is very little descending to recover on. Every kilometre you ride is a kilometre of altitude earned.

Pacing Notes

On a climb this long, discipline beats bravado. The first job is protecting your FTP — if you know your threshold power, you can anchor the entire 28.8 km to a percentage of it and hold that number honestly, especially through the steep ramps where the temptation to surge is strongest. Aim to sit slightly below threshold on the average-gradient sections and accept a brief cost above it when the road tips toward 21.82%, then bring the effort back down as the pitch eases. If you are unsure of your current threshold, run the numbers first with the FTP estimator so your target reflects today's fitness rather than a guess. Gaining 2216 m in one push rewards even pacing far more than heroics on the lower slopes.

Gearing

For an HC climb of this length with ramps near 22%, gear low and gear generously. A compact 34-tooth chainring paired with a 34×32 setup is the sensible baseline for strong climbers, giving you a manageable cadence on the 7.7% average sections. But given the 21.82% maximum, most riders will be far happier reaching for a 34×34, which buys crucial cadence on the steepest walls and keeps your knees and pacing intact over 28.8 km. When in doubt on a climb this severe, take the easier ratio — spinning a low gear beats grinding to a halt.

Summary

The Col de Nannaz is a true HC test: long, high, and steep in the wrong places. Respect the distance, protect your threshold, and gear for the worst ramps rather than the average.

Length: 28.8 km
Average gradient: 7.7%
Max gradient: 21.82%
Start: 431 m
Summit: 2647 m
Net gain: 2216 m
Total ascent: 2205 m
Category: HC