Colle Portola

Overview

Colle Portola is a genuine hors catégorie monster. Over 21.7 km it climbs from a start elevation of 524 m to a summit at 2404 m, a net elevation gain of 1880 m with 1851 m of total ascent packed into that single, unbroken push. The average gradient is a punishing 8.67%, and the road spikes to a maximum of 19.31% — the kind of ramp that forces you out of the saddle whether you planned it or not.

This is not a climb of gentle warm-ups and false flats. The near-identical net gain and total ascent numbers tell you almost everything: there is very little respite, no descending to reset the legs, just a long, sustained grind toward the sky. Getting the effort right from the bottom is the whole game.

How the Gradient Unfolds

The headline figure is that 8.67% average held across the full 21.7 km. On most climbs the average hides pockets of recovery, but here the difference between the 1880 m of net gain and 1851 m of total ascent is tiny — meaning the elevation profile marches almost straight upward. What flattening exists is minimal and short-lived.

The 19.31% maximum is the sting in the tail of this profile. Whether it arrives early or late, that ramp sits more than 10 points above the average, so it will feel savage against legs already loaded by a sustained sub-9% grade. Treat the whole ascent as one continuous block of high-8% climbing punctuated by steeper walls, and you will not be caught out.

Pacing Notes

On a climb this long and this steep, discipline beats bravado. At roughly 8.67% for 21.7 km, most riders spend the entire effort near or just below threshold, so your FTP is the single most useful number you have. Anchor your pacing to a percentage of it and refuse to chase surges — the 1880 m of vertical will be settled by consistency, not heroics.

If you are not sure of your current threshold, run the numbers through the FTP estimator before you commit to a target. Bank a small cushion for the 19.31% max ramp, because spiking hard there and blowing up leaves a lot of mountain still to climb. Aim to arrive at the 2404 m summit having ridden within yourself the whole way.

Gearing

Gear for survival, not ego. For an HC climb averaging 8.67% with pitches to 19.31%, a compact chainring paired with a wide-range cassette is the right foundation. A 34×32 is the sensible baseline for strong climbers, giving you a low enough ratio to spin the sustained sections without grinding.

But given the 19.31% max and the sheer 1880 m of gain, most riders will be far happier with a 34×34. That extra sprocket buys you cadence on the steepest ramps and protects your legs across the full 21.7 km. When in doubt, take the easier gear — you cannot shift lower than you brought.

Summary

Colle Portola earns its HC rating honestly: 21.7 km, 8.67% average, and a 19.31% max that never lets you settle, all the way from 524 m to 2404 m. Pace it by your threshold, gear generously, and respect the mountain.

Length: 21.7 km
Average gradient: 8.67%
Max gradient: 19.31%
Start: 524 m
Summit: 2404 m
Net gain: 1880 m
Total ascent: 1851 m
Category: HC