Colle San Carlo

Overview

Colle San Carlo is one of those climbs whose numbers tell the whole brutal story before you turn a pedal. Over just 6.7 km it averages a merciless 14.85%, hauling you from a start elevation of 923 m up to a summit at 1920 m. That is a net gain of 997 m packed into well under seven kilometres, which is exactly why it wears the HC label — hors catégorie, the hardest rung on the ladder, above even category 1. There is nothing gentle here and nowhere to truly recover. This is a climb you survive, not one you dance up.

How the Gradient Unfolds

An average of 14.85% is already extreme, but averages hide the teeth. With a maximum gradient of 26.22%, the steepest sections here more than double the difficulty of the mean. On a wall like this, the gradient rarely dips into anything resembling relief; instead it oscillates between "very hard" and "barely rideable," with the harshest ramp hitting that 26.22% figure.

The elevation profile is telling: a net gain of 997 m against a total ascent of 961 m means the road climbs relentlessly with only tiny, almost negligible descents — the two figures are within 36 m of each other. In practical terms, you are going up the entire way. Expect the gradient to bite hardest wherever the road pinches, and treat every visible easing as temporary.

Pacing Notes

On a climb this steep, pacing is less about clever surges and more about not blowing apart in the first kilometre. Because the average sits at 14.85%, most riders will spend the entire ascent at or above their threshold, so knowing your FTP is essential for judging how long you can hold each ramp. If you do not have a current number, run the FTP estimator before you attempt this.

Aim to arrive at the base with reserves, settle into the lowest sustainable rhythm you can find, and accept that the 26.22% pitches will spike your effort no matter how disciplined you are. Better to lose seconds early than to redline before the halfway point of the 6.7 km.

Gearing

Do not under-gear this one. Standard compact gearing that feels fine on ordinary climbs will leave you grinding or walking here. A 34×32 is the sensible minimum for strong climbers, but given the 14.85% average and 26.22% max, most riders will be far happier — and far more likely to keep turning the pedals — on a 34×34. If your bike allows an even easier ratio, use it: on a 997 m HC wall, a cadence you can actually sustain matters more than pride.

Summary

Colle San Carlo is a short, savage HC test defined by its 14.85% average and 26.22% max over 6.7 km. Bring your lowest gears, respect the opening ramps, and pace to your threshold — the summit at 1920 m rewards patience over bravado.

Length: 6.7 km
Average gradient: 14.85%
Max gradient: 26.22%
Start: 923 m
Summit: 1920 m
Net gain: 997 m
Total ascent: 961 m
Category: HC