Colletto del Gui

Overview

Colletto del Gui is an hors catégorie climb in Italy, and the numbers tell you why it earns the top rating. Over 14.6 km the road averages a brutal 9.37% and lifts you from 1071 m at the base to 2437 m at the summit — a net gain of 1366 m with 1348 m of total ascent. There is no easing into this one. An average approaching double digits held across nearly fifteen kilometres is the kind of sustained effort that separates HC ascents from everything below them, and the 22.3% maximum gradient means the hardest ramps are far steeper than the average alone suggests.

How the Gradient Unfolds

The defining feature of Colletto del Gui is relentlessness. With a 9.37% average sustained over 14.6 km, there are effectively no recovery sections to hide in — the mean gradient is close enough to the peak that flatter stretches, if they exist at all, are brief. The spread between the 9.37% average and the 22.3% maximum tells the real story: pitches that jump nearly 13 points above the average will pin you against the bars. Because the climb tops out at 2437 m, the upper reaches also carry the thin-air penalty of high altitude, so the final kilometres feel harder than the same gradient would lower down. Expect the effort to compound as you climb.

Pacing Notes

On a climb this long and this steep, pacing is everything — go out too hard and the 22.3% ramps late on will end your day. Anchor your effort to your FTP and hold a disciplined, sustainable power target from the base. With 1366 m to gain, treat the first kilometres as investment, not a race, and save headroom for the steepest pitches. If you are unsure of your threshold, run the numbers through the FTP estimator before you commit to a target, then ride just under it so the altitude near 2437 m does not blow you apart in the final third.

Gearing

Do not under-gear this climb. A 9.37% average over 14.6 km with 22.3% spikes demands the easiest cassette you can fit. A compact 34-tooth chainring paired with a 34×32 setup is the sensible minimum for strong climbers, but most riders will be far happier with 34×34, which gives you a spin-friendly ratio for the steepest ramps and lets you protect your legs across the full 1366 m of ascent. If your bike allows an even wider range, take it — on an HC climb topping out at 2437 m, spare gears are never wasted.

Summary

Colletto del Gui is a genuine hors catégorie test: long, unbroken and steep from bottom to top, finishing high enough that altitude adds its own tax. Pace it to your threshold, gear it generously, and respect the 22.3% ramps that punctuate the 9.37% average.

Length: 14.6 km
Average gradient: 9.37%
Max gradient: 22.3%
Start: 1071 m
Summit: 2437 m
Net gain: 1366 m
Total ascent: 1348 m
Category: HC