Colla Rossa

Overview

Colla Rossa is a hors catégorie (HC) climb in France, the top tier in cycling's difficulty scale and reserved for the hardest ascents. It runs 12.1 km from a start elevation of 693 m to a summit at 2,169 m, delivering a net elevation gain of 1,476 m. At an average gradient of 12.19%, this is not a climb you settle into — the mean pitch alone puts it among the steepest sustained efforts a rider can face over this distance.

The headline stat undersells the work. While the net elevation gain is 1,476 m, the total ascent is 1,783 m — a gap of 307 m. That means the road gives back roughly 307 m of descent along the way, and every metre you drop has to be re-climbed. The profile is not a clean ramp; it undulates, and those dips cost you rhythm and force repeated hard restarts rather than one continuous grind.

How the Gradient Unfolds

A 12.19% average across 12.1 km hides real variation. Descents and flatter shelves drag the mean down, which means the climbing sections sit well above 12.19% to compensate. Expect the effort to arrive in blocks rather than a single smooth wall, with the steepest ramps punching hard after brief lulls.

• Short recovery or descending sections that account for the 307 m of re-climbing
• Repeated steep pitches that sit above the 12.19% average to offset the flatter parts
• A steepest ramp that will spike well into double digits and demand your lowest gear

Pacing Notes

On an undulating climb like this, chase even effort, not even speed. Your pace will swing wildly across the profile, so hold a steady sustainable power output through the steep pitches and resist the urge to hammer the brief flatter sections to "make up time." The 307 m of re-climbing punishes riders who spike their power on the ramps and blow up before the summit at 2,169 m. If you do not know your ceiling, run the numbers through our FTP estimator before you commit to a target for the day.

Gearing

The steep pitches govern your gearing here, not the average. On a climb averaging 12.19% with ramps steeper still, a compact or sub-compact chainset paired with a wide-range cassette is not optional — think 34×32 or 34×34 to keep your cadence alive when the road kicks up. Check your setup before the ride. Confirm the cassette and chainset you have actually give you a low enough bailout gear; arriving at the steepest ramp under-geared on an HC climb is how a hard day becomes a walk.

Summary

• Length: 12.1 km
• Average gradient: 12.19%
• Net elevation gain: 1,476 m
• Total ascent: 1,783 m
• Category: HC

Colla Rossa is a genuine HC test: 12.1 km at 12.19% average, gaining 1,476 m net but 1,783 m in total once the undulations are counted. Pace by effort, gear for the steepest ramp, and respect the 307 m of hidden re-climbing.