Colle Ciarbonet

Overview

Colle Ciarbonet is a hors catégorie climb, the hardest rating a road ascent can carry. It stretches 22.1 km from a valley floor at 978 m up to a summit of 2602 m, delivering 1624 m of net elevation gain. The average gradient sits at a relentless 7.34%, and the total ascent of 1667 m tells you the road never truly gives your legs a rest — there are barely any downhill metres to reclaim. This is a full-length HC effort where the difficulty comes not from a single wall but from the sheer duration spent climbing at a punishing average.

How the Gradient Unfolds

The defining number here is length. At 22.1 km, Ciarbonet asks more than an hour of sustained climbing from most riders, and the 7.34% average means there is nowhere to truly recover. The spread between the 7.34% average and the 37.09% maximum is enormous — a difference of nearly 30 percentage points — which signals that at least one section rears up into extreme, out-of-the-saddle territory. Because total ascent (1667 m) exceeds net gain (1624 m) by only 43 m, the profile is almost monotonically upward: no meaningful false flats or descents to break the rhythm. Expect a long, grinding lower and middle third, then a sting somewhere on the way to 2602 m where the road bites hardest.

Pacing Notes

On a climb this long, discipline beats bravado. Anchor your effort to your FTP and treat the first two-thirds as a controlled, steady tempo — going deep early on a 22.1 km ascent is the classic way to blow up before the summit. Aim to hold a consistent power band through the sustained 7.34% sections, then keep something in reserve for the 37.09% pitch, where you may briefly redline no matter how well you meter yourself. If you're unsure what wattage that steady effort should be, run the numbers through the FTP estimator before you commit to a target for the day. At 2602 m of summit elevation, thinning air will also nibble at your ceiling, so build in a small margin.

Gearing

Do not under-gear this one. With a 7.34% average sustained over 22.1 km and a maximum of 37.09%, you want the widest range you can fit. A compact 34-tooth front paired with at least a 34×32 rear is the sensible floor for most fit amateurs, and a 34×34 is the smarter call — that extra sprocket buys you a survivable cadence when the road hits its steepest ramp and your legs are already deep into 1624 m of accumulated climbing. If your setup allows an even larger cassette, you will not regret it here.

Summary

Colle Ciarbonet is a genuine HC test: long, steep, and unforgiving from 978 m all the way to 2602 m. Respect the 22.1 km distance, gear low, pace to your numbers, and save a match for that 37.09% ramp.

Length: 22.1 km
Average gradient: 7.34%
Max gradient: 37.09%
Start: 978 m
Summit: 2602 m
Net gain: 1624 m
Total ascent: 1667 m
Category: HC