Porta Renzola

Overview

Porta Renzola is an HC climb — hors catégorie, the hardest tier, above categories 1, 2, 3 and 4 — and the numbers make the case immediately. It covers just 5.9 km, yet averages a savage 15.61%. Over that short distance it lifts you from a start elevation of 482 m to a summit of 1406 m, a net elevation gain of 924 m. This is not a climb you settle into; it is one you survive. When a road averages north of 15% for nearly six kilometres, there is no easy stretch waiting around the corner to bail you out.

How the Gradient Unfolds

The defining feature here is consistency of severity. With a 15.61% average sustained across 5.9 km, Porta Renzola offers almost nowhere to recover. The net gain of 924 m against a total ascent of 908 m tells you the road climbs steadily and almost never gives back what you have won — there is minimal descending or false-flat inside the effort. Practically, expect the gradient to pin you above threshold from the opening ramps and hold you there. On a wall this steep, momentum is fragile: lose your rhythm and the road will not hand it back. Treat the whole 5.9 km as a single sustained effort rather than a sequence of distinct sections, because the elevation profile behaves that way.

Pacing Notes

On a climb this steep, pacing is really power management. Your sustainable ceiling here is your FTP — the power you can hold for roughly an hour — and on a 15.61% wall you will be riding at or above it for much of the 5.9 km. If you do not know your number, estimate it with the FTP estimator before you commit, because guessing wrong on a climb like this ends the day early. The smart approach is to start conservatively: the temptation on the lower ramps is to attack, but with 924 m of climbing still ahead, restraint in the first third pays back over the final kilometres. Keep cadence as high as the gradient allows and settle into a repeatable effort rather than chasing surges you cannot sustain.

Gearing

Do not under-gear this one. A 15.61% average over 5.9 km punishes anyone forced to grind at low cadence. A compact 34-tooth chainring paired with a 34×32 low gear is the practical minimum for most fit riders, and even then you will be turning it over slowly on the steepest ramps. If you climb at lower cadence, carry extra weight, or simply want to protect your knees, go to 34×34 — that extra sprocket buys real breathing room across nearly six kilometres of unrelenting pitch. The goal is to keep the cranks moving; on a wall this steep, a bigger cassette is not a weakness, it is what lets you finish.

Summary

Porta Renzola is a short, ferocious HC test: 5.9 km that never relents, averaging 15.61% and gaining 924 m to top out at 1406 m. Gear low, start controlled, and respect the gradient — this is one of the purest sustained-steepness efforts you can ride.

Length: 5.9 km
Average gradient: 15.61%
Max gradient: n/a
Start: 482 m
Summit: 1406 m
Net gain: 924 m
Total ascent: 908 m
Category: HC