Col de Chétillon

Overview

Col de Chétillon is a hors catégorie climb that earns its rating on numbers alone. Over 16.8 km the road drags you from a base at 390 m to a summit at 1874 m — a net gain of 1484 m — at an average gradient of 8.83%. That average is the headline, because on a climb this long, holding nearly 9% for the better part of an hour is what separates HC from everything below it. The steepest pitch bites at 23.13%, a wall that forces a decision long before you reach it: pace conservatively early, or pay for it later. This is not a climb you attack. It's a climb you survive first and race second.

How the Gradient Unfolds

The defining tension of Chétillon is the gap between what the average promises and what the road actually delivers. An 8.83% mean across 16.8 km already means there is almost no relief — few flat recovery sections, no soft-pedalling. But the 23.13% max tells you the gradient is not uniform. Somewhere on this climb the road pitches to more than two and a half times the average, and to keep the mean at 8.83% those brutal ramps must be balanced by long stretches sitting only slightly below it. In practice that means the "easier" kilometres are still around 8%, and the hard ones are savage. Note too the difference between net gain and total ascent: 1484 m net versus 1451 m of total climbing. That the recorded ascent sits below the net figure points to steady, relentless uphill with negligible descending — you climb, and you keep climbing.

Pacing Notes

On a climb of this length and steepness, your effort ceiling matters more than your top-end power. Anchor your pace to your FTP: for a sustained HC effort, most riders target a fraction of that threshold they can hold for 45 minutes or more, then leave headroom for the 23.13% ramp so it doesn't blow the whole ride apart. If you don't know your threshold, run the numbers through the FTP estimator before you commit. The mistake here is starting near the base as if the average were the whole story — it isn't. Ride the first kilometres a notch under what feels sustainable, keep cadence high, and treat the steepest wall as the one place you're allowed to redline, because there's no faking your way up 23.13%.

Gearing

Gear for the wall, not the average. At 8.83% for 16.8 km a compact chainring is essential, and the 23.13% max means your smallest gear needs to be genuinely small. A 34×32 is the minimum I'd bring, and for most riders it will feel marginal when the road stands up. If your derailleur clears it, a 34×34 is the smarter choice — that extra sprocket buys you cadence exactly where a 34×32 would grind you to a crawl. On a climb gaining 1484 m in one push, spinning a slightly easier gear preserves your legs far more than muscling a bigger one.

Summary

Col de Chétillon is a full-length HC test: long, steep, and unforgiving, with a wall steep enough to end your day if you arrive at it empty. Pace to threshold, gear for the ramps, and respect the distance.

Length: 16.8 km
Average gradient: 8.83%
Max gradient: 23.13%
Start: 390 m
Summit: 1874 m
Net gain: 1484 m
Total ascent: 1451 m
Category: HC