Col du Serpentin

Overview

The Col du Serpentin is a category 1 climb that trades brutality for length. Over 17.9 km it averages 5.82%, lifting you from a valley start at 782 m to a summit at 1822 m. On paper that is a net gain of 1040 m, though the recorded total ascent of 999 m tells you the road does not climb in a single unbroken line — there are false flats and brief respites folded into the profile. This is a climb you settle into rather than attack. At nearly 18 km, it rewards patience, rhythm and a cool head far more than raw explosiveness.

How the Gradient Unfolds

A 5.82% average across 17.9 km sounds moderate, and in isolation each kilometre is. What makes the Serpentin a category 1 rather than something gentler is duration: you are asked to hold a tempo effort for the better part of an hour. The gap between the 1040 m net gain and the 999 m of total ascent is the clue to its shape — roughly 40 m of that vertical is effectively given back somewhere along the way, meaning the working sections sit above the headline average. Expect the road to breathe: pitches that bite a little harder, then a flatter passage where you can recover before the next ramp. No single wall defines this climb; the accumulated metres do.

Pacing Notes

The Serpentin is won or lost in the first third. With 17.9 km ahead, going out above your sustainable ceiling means paying interest for the remaining hour. Anchor your effort to your FTP: most riders should target a steady tempo comfortably below threshold and only lift into the harder pitches when the gradient forces it. If you do not know your number, run it through the FTP estimator before you plan your pacing. On a climb this long, holding an even power line will beat any surge-and-fade strategy — the flatter passages are for recovering your legs, not for spending matches.

Gearing

For a 17.9 km climb averaging 5.82%, comfortable gearing beats heroic gearing every time. A compact 34-tooth inner chainring paired with a 34×32 cassette is a sensible baseline for strong riders who want to keep the cadence up through the steeper ramps. If you weigh more, ride tired, or simply prefer to spin, step up to a 34×34 — the extra range costs nothing on the flatter sections and buys you a spinnable gear when the pitches stack late in the climb. On a col of this length, protecting your cadence protects your legs; err toward the easier ratio.

Summary

The Col du Serpentin is a classic long tempo climb: 17.9 km at 5.82%, no single savage wall, just a steady demand to hold your rhythm from 782 m all the way to 1822 m. Pace it evenly, gear it generously, and let the 1040 m of ascent come to you.

Length: 17.9 km
Average gradient: 5.82%
Max gradient: n/a
Start: 782 m
Summit: 1822 m
Net gain: 1040 m
Total ascent: 999 m
Category: 1