Colle del Loo

Overview

Colle del Loo is a long, serious ascent: 21.9 km of continuous climbing that lifts you from 287 m at the base to 1552 m at the summit. That is a net gain of 1265 m, with 1245 m of total ascent packed into the effort. The category 1 rating tells you what to expect — one rung below hors catégorie, this is a climb that rewards patience and punishes anyone who goes out too hard. The 5.78% average gradient sounds moderate, but averages hide the truth here. Buried inside is a ramp touching 27.67%, a wall steep enough to reshape how you ride the entire climb.

How the Gradient Unfolds

Do the math and the shape becomes clear. An average of 5.78% across 21.9 km is a steady, grinding incline — the kind that never truly lets you rest but rarely forces you out of the saddle either. The gap between that 5.78% mean and the 27.67% maximum is enormous, which means the difficulty is not evenly spread. For long stretches you will sit slightly below the average, banking energy, only to be met by pitches that spike far above it. The 27.67% max is more than four and a half times the average gradient, so treat the climb as a rolling negotiation between recovery stretches and short, ferocious ramps rather than a single constant effort.

Pacing Notes

On a climb this long, discipline beats bravado. Your FTP is the single most useful number for planning Colle del Loo — over 21.9 km you simply cannot ride above threshold and expect to survive the steep pitches near the top. Aim to hold a sustainable percentage of threshold on the steady sections so you keep something in reserve for the 27.67% wall, where power spikes are unavoidable and cadence collapses. If you do not know your current threshold, run the numbers through the FTP estimator before you commit to a pace. With 1265 m of climbing ahead, going five percent too hard in the first third will cost you far more than it saves.

Gearing

Gearing is where Colle del Loo separates the prepared from the optimistic. The 5.78% average is manageable on almost any setup, but the 27.67% max gradient is not — that pitch alone justifies your easiest possible ratio. A compact chainring paired with a wide-range cassette is the sensible baseline. A 34×32 will get most fit riders up the steady sections comfortably, but for the steepest ramps you will be grateful for a 34×34, which gives you a genuine bail-out gear when the road tilts toward 27.67%. If your bike accepts anything easier still, use it; on a 21.9 km climb with walls this severe, spinning a low gear always beats grinding to a standstill.

Summary

Colle del Loo is a long, honest category 1 climb defined by its length and one brutal pitch. Come with low gearing, a paced threshold effort, and respect for the numbers.

Length: 21.9 km
Average gradient: 5.78%
Max gradient: 27.67%
Start: 287 m
Summit: 1552 m
Net gain: 1265 m
Total ascent: 1245 m
Category: 1