Alto de Garajonay

Overview

Alto de Garajonay is a hors catégorie climb, the hardest rating in cycling, and the numbers explain why. Over 16.6 km it averages 8.44%, lifting you from a start elevation of 78 m to a 1478 m summit. That is 1400 m of net gain, with 1392 m of total ascent packed into a single sustained effort. There is nowhere on this climb to genuinely recover — the average alone would tax most riders, and the road throws a 24.13% pitch at you before it is done. Treat it as a full HC test of both fitness and pacing discipline.

How the Gradient Unfolds

The defining feature of Garajonay is relentlessness. An 8.44% average across 16.6 km means the road rarely dips into anything you would call easy. With net gain of 1400 m and total ascent of 1392 m almost identical, there are effectively no descents to break the rhythm — every metre of forward progress is a metre of climbing. The 24.13% maximum is nearly three times the average, so expect at least one wall-like ramp where the gradient briefly detonates. The gap between that spike and the 8.44% mean is the number to respect: the climb is hard everywhere and savage in places.

Pacing Notes

On a climb this long and this steep, pacing is everything. Anchor your effort to your FTP rather than to how you feel in the opening kilometres, where fresh legs tempt you to overcook it. A sustainable target for a sixteen-plus kilometre HC effort sits at or just below threshold, leaving a small reserve for the 24.13% ramp — that pitch will spike your power far above threshold no matter how disciplined you are, so bank the headroom in advance. If you do not know your threshold number, run it through the FTP estimator before you start, then hold that ceiling steadily from 78 m all the way to the 1478 m summit.

Gearing

At 8.44% average with a 24.13% maximum, gearing is not a luxury — it is survival. For most amateur riders a compact 34-tooth chainring paired with a wide cassette is the baseline. A 34×32 will get you up the sustained sections, but on a climb with 1400 m of net gain and a near-25% wall, many riders will be far happier with 34×34, which drops your minimum cadence-preserving gear low enough to keep the legs turning rather than grinding to a stall. If your bike can take it, err toward the easier ratio; you will never regret spare gears on an HC climb, and you will always regret running out of them at 24.13%.

Summary

Alto de Garajonay is a genuine hors catégorie challenge: long, unremittingly steep, and topped with a brutal ramp. Respect the 8.44% average, save something for the 24.13% wall, and gear low. Do that, and the 1478 m summit is yours.

Length: 16.6 km
Average gradient: 8.44%
Max gradient: 24.13%
Start: 78 m
Summit: 1478 m
Net gain: 1400 m
Total ascent: 1392 m
Category: HC