Col du Viallet

Overview

Col du Viallet is a genuine hors catégorie (HC) test — the hardest classification cycling hands out, sitting above categories 1 through 4. Over 11.4 km the road lifts you from 1054 m at the base to a 2248 m summit, a net gain of 1194 m. What sets it apart is the average gradient: 10.45%. That is not a number you meet on rolling foothills. It is a sustained double-digit wall that barely lets up across the entire ascent, and it puts Viallet squarely among the climbs where survival, not speed, is the first objective.

How the Gradient Unfolds

The defining feature here is consistency of severity. With an average of 10.45% held over 11.4 km, there are no long recovery flats to bank on. The total ascent of 1366 m against a net gain of 1194 m tells you there is a modest amount of undulation — roughly 172 m of extra up-and-down folded into the profile — but do not read that as relief. On a climb this steep, even a brief easing to single digits feels like a gift, and any dip is quickly repaid. Plan your effort around the assumption that the gradient rarely drops below the average for long. Starting already at 1054 m and finishing at 2248 m, you also spend the whole climb at real altitude, where thinner air quietly trims the power you can hold.

Pacing Notes

On an 11.4 km climb averaging 10.45%, pacing is everything. Go out above your sustainable ceiling in the first two kilometres and the back half will unravel completely. Anchor your effort to your FTP: most riders should target a fraction of it that they can hold for a long, steady time-trial-style effort, since the summit at 2248 m is a long way up. If you are unsure of your current number, run the FTP estimator before you commit to a plan. Keep your cadence honest, meter your matches carefully, and treat any shallower ramp as a chance to recover heart rate rather than to attack.

Gearing

At 10.45% average over 11.4 km, gearing is not a luxury — it is the difference between spinning and grinding to a halt. A compact 34-tooth front paired with a wide-range cassette is the sensible baseline. A 34×32 will get many trained riders up, but on gradients this sustained a 34×34 gives you the extra margin to keep your cadence spinning instead of mashing, which protects your legs for the full 1194 m of climbing. If your bike can take an even easier bailout gear, you will not regret it on the steepest pitches near the 2248 m top.

Summary

Col du Viallet is a short-but-brutal HC climb defined by one thing: relentless steepness. 11.4 km at 10.45% to a 2248 m summit is a serious day, and respecting the numbers with smart pacing and generous gearing is the only way to enjoy it.

Length: 11.4 km
Average gradient: 10.45%
Max gradient: n/a
Start: 1054 m
Summit: 2248 m
Net gain: 1194 m
Total ascent: 1366 m
Category: HC