Col de Sobe

Overview

The Col de Sobe is a hors catégorie climb, the hardest classification on the road, and its numbers explain why. From a start elevation of 676 m it hauls you up 29.5 km to a summit at 2248 m — a net gain of 1572 m at an average gradient of 5.33%. That average is deceptively friendly. A climb this long asks for sustained output over the better part of an hour or more, and the 18.37% max gradient means there are pitches that will spike your effort well beyond anything the mean suggests. This is a ride you meter out, not one you attack.

How the Gradient Unfolds

A 5.33% average across 29.5 km is a moderate slope on paper, but averages hide the shape of a climb. The gap between the 5.33% mean and the 18.37% max tells you the ascent is uneven: long stretches sit below the average to make room for the ramps that reach nearly 18.37%. Note too that the total ascent of 1508 m is slightly less than the 1572 m net elevation gain — a small discrepancy that points to brief flatter or descending sections woven into the climb. Those respites are where you recover; the steep pitches are where the climb is won or lost. Expect to shift constantly rather than settle into a single rhythm.

Pacing Notes

Over 29.5 km, discipline beats bravado. Anchor your effort to a percentage of your FTP rather than to how you feel in the opening kilometres, where fresh legs tempt you to overspend. On a climb this long, a few extra watts held too early compound into a hard bonk before the 2248 m summit. If you do not know your threshold, run the numbers through the FTP estimator first and set a target power you can genuinely hold for the full duration. On the 18.37% ramps, let cadence drop and power surge briefly, then reel it back on the shallower sections that follow. Treat the flatter parts within the total ascent as active recovery, not as an invitation to push.

Gearing

Gear for the max, not the average. The 18.37% pitches are what dictate your setup, and on a 1572 m ascent you will meet them with tired legs. A compact 34-tooth chainring paired with a wide-range cassette is the sensible baseline. A 34×32 will get most riders up the shallower majority comfortably, but it can feel marginal when the road tilts toward 18.37% late in the climb. If you have any doubt about your climbing legs or your target power over 29.5 km, fit a 34×34 — the extra sprocket buys you cadence and spares your knees on the steepest ramps. Err toward easier here; you cannot spin a gear you did not bring.

Summary

The Col de Sobe is a genuine HC test: long, steep in bursts, and unforgiving of a poor early pace. Respect the distance, gear low, and ration your effort against your threshold, and its 1572 m of climbing becomes a rewarding day rather than a survival exercise.

Length: 29.5 km
Average gradient: 5.33%
Max gradient: 18.37%
Start: 676 m
Summit: 2248 m
Net gain: 1572 m
Total ascent: 1508 m
Category: HC