Passo di Rostagno

Overview

Passo di Rostagno is a hors catégorie (HC) climb, the top of the difficulty scale before the numbered categories 1 through 4. It stretches 23.5 km from a valley start at 717 m to a summit of 2346 m, a net elevation gain of 1629 m at an average gradient of 6.94%. The total ascent tallies 1606 m, meaning the road climbs almost continuously with only slight variation — there is very little false-flat relief to break the effort. At 23.5 km, this is a climb measured in tens of minutes, not seconds, and it rewards patience over aggression.

How the Gradient Unfolds

The defining number here is consistency. An average of 6.94% held across 23.5 km is a steady, grinding slope rather than a wall. But the max gradient of 15.26% tells you the road is not uniform: expect ramps that spike to more than double the average, demanding sharp increases in torque. Because net gain (1629 m) exceeds total ascent (1606 m) only marginally, you know the climb almost never gives elevation back — the road ticks upward nearly the whole way. The pattern to expect is long stretches near the 6.94% average punctuated by steeper pitches climbing toward that 15.26% ceiling. Reading the road ahead and easing off before the steep ramps is the key skill.

Pacing Notes

Over 23.5 km, pacing discipline decides your day. Ride the early kilometres well below threshold; the length means a hot start compounds badly across 1629 m of gain. Anchor your effort to your FTP and aim to sit comfortably beneath it on the average-gradient sections, saving headroom for the pitches toward 15.26%. If you do not know your threshold, run the numbers through the FTP estimator before you start planning. On a climb this long, riding just above FTP for a few minutes too early can cost you far more than the time saved. Treat the steep ramps as short, contained surges and settle straight back to your target on the far side.

Gearing

With 23.5 km at 6.94% and ramps reaching 15.26%, gearing is not a luxury — it is what keeps your cadence alive over 1629 m of climbing. A compact 34-tooth inner chainring is the baseline. Pair it with at least a 34×32, which gives most riders a workable cadence on the average slope. For the steepest pitches near 15.26%, or if you want insurance late in a 23.5 km effort when your legs are fading, step up to a 34×34. The larger sprocket lets you spin rather than grind, protecting your knees and preserving power for the summit push to 2346 m. When in doubt on an HC climb this long, choose the easier gear.

Summary

Passo di Rostagno is a true endurance HC climb: long, steady, and unrelenting, with just enough steep punctuation to keep you honest. Pace it conservatively, gear it generously, and respect the full 23.5 km.

Length: 23.5 km
Average gradient: 6.94%
Max gradient: 15.26%
Start: 717 m
Summit: 2346 m
Net gain: 1629 m
Total ascent: 1606 m
Category: HC