Alto de Cardenillo

Overview

Alto de Cardenillo is a hors catégorie (HC) climb that asks everything of you and then asks a little more. Over 31.5 km it rises from a start elevation of 2002 m to a summit of 3919 m — a net elevation gain of 1917 m. The average gradient of 6.08% sounds civil on paper, but stretch that number across 31.5 km and the arithmetic turns brutal: this is an hour-plus of sustained effort at altitude, with a total ascent of 2088 m once you account for the small dips and false flats along the way. The gap between 1917 m of net gain and 2088 m of total ascent tells you there are 171 m of hidden climbing tucked into recoveries that never quite let you recover.

How the Gradient Unfolds

The headline number to respect is the max gradient of 15.72% — more than double the average. A climb that averages 6.08% but spikes past 15% is not a metronomic drag; it is a rhythm-breaker. Expect the road to oscillate, with stretches near the 6% mean punctuated by pitches that force you out of the saddle. Because the total ascent (2088 m) exceeds the net gain (1917 m) by 171 m, there are descents and flatter reprieves built in — but every metre you lose has to be climbed back. The real difficulty compounds as you go: the final kilometres arrive above 3500 m, where the summit at 3919 m leaves you gasping in genuinely thin air.

Pacing Notes

At 31.5 km, discipline beats bravado. Anchor your effort to a percentage of your FTP and hold it — the 15.72% ramps will tempt you to surge, but a single over-cooked pitch this early can unravel the whole hour. Aim to sit just under threshold on the 6% sections and accept that the steep pitches will push you briefly over; the average smooths out if you don't panic. Altitude matters enormously here: above 3000 m your sustainable power drops, so the wattage that feels easy at the 2002 m start will feel very different near the 3919 m summit. If you don't know your number, run it through the FTP estimator before you plan your climb.

Gearing

For an HC effort of this length with pitches to 15.72%, gear low and gear early. A compact 34-tooth chainring paired with a wide cassette is the sensible baseline. A 34×32 will get most riders up the sustained 6.08% sections, but on the 15.72% ramps — especially fatigued and oxygen-starved near 3919 m — you will wish for more. If your rear derailleur allows it, run a 34×34 so you can keep the cadence spinning rather than grinding. On a climb that gains 1917 m net, spare knees are worth more than spare cogs.

Summary

Alto de Cardenillo is a summit that earns its HC rating through sheer scale: long, high, and steep in all the wrong places. Pace it by power, gear it low, and respect the altitude.

Length: 31.5 km
Average gradient: 6.08%
Max gradient: 15.72%
Start: 2002 m
Summit: 3919 m
Net gain: 1917 m
Total ascent: 2088 m
Category: HC