Col de Cou

Overview

The Col de Cou is a climb with almost nowhere to hide. Over 10.1 km it averages 9.15%, lifting you from a start elevation of 991 m to a summit at 1917 m. That is 926 m of net elevation gain packed into just over ten kilometres, and the total ascent of 1301 m tells you the road is not a single clean ramp — it rolls and pitches enough to add extra vertical along the way. It carries an HC rating, hors catégorie, the label reserved for the hardest climbs, above categories 1, 2, 3 and 4. Everything about the numbers here says the same thing: this is a sustained, uncompromising effort.

How the Gradient Unfolds

A 9.15% average across 10.1 km is punishing because it leaves little room for recovery. On a climb like this, the gradient is rarely exactly at the mean — some sections sit below 9.15% and others rise well above it. The gap between the 926 m net gain and the 1301 m total ascent confirms there are pitches steeper than the average, along with short reprieves where the road eases or briefly descends before climbing again. Read the shape as a wall that occasionally flexes rather than a smooth escalator. The lower slopes near 991 m and the upper reaches approaching 1917 m both demand respect; there is no genuine flat to hide in.

Pacing Notes

The single biggest mistake on a 9.15% climb is starting too hard. With 10.1 km ahead of you, discipline in the opening kilometres pays off enormously. Anchor your effort to your FTP: on a sustained HC climb like this you want to settle just below threshold and hold it, saving any surplus for the steeper-than-average pitches. If you are unsure of your number, run the FTP estimator before you go so your target power is grounded in data rather than feel. Climbing 926 m of net gain is a long time under load, so aim for an intensity you could theoretically sustain to the summit, then release it only on the harder ramps.

Gearing

Do not undergear the Col de Cou. A 9.15% average sustained for 10.1 km will grind down anything too tall long before the 1917 m summit. A compact 34-tooth inner ring paired with a wide-range cassette is the sensible baseline. A 34×32 is the minimum most riders should consider here, and it will feel marginal on the steeper pitches implied by the 1301 m of total ascent. If you have any doubt about your climbing legs or your endurance over 926 m of gain, fit a 34×34 instead — the extra sprocket buys you a lower cadence-preserving gear that keeps your effort near threshold rather than forcing a lurch into the red.

Summary

The Col de Cou is a proper HC test: 10.1 km, 9.15% average, and 926 m of net gain from base to summit. Pace it to your threshold, gear low, and treat every steeper-than-average ramp as the moment to spend, not to panic.

Length: 10.1 km
Average gradient: 9.15%
Max gradient: n/a
Start: 991 m
Summit: 1917 m
Net gain: 926 m
Total ascent: 1301 m
Category: HC