Alto del Bosque

Overview

Alto del Bosque is a short climb that behaves like a much longer one. Over just 4.5 km it averages a savage 13.44%, and that number alone tells you almost everything you need to know: this is not a road you settle into, it is a wall you survive. It is rated HC — hors catégorie, the hardest grade above categories 1 through 4 — and it earns the label on gradient alone rather than length. From a start elevation of 1607 m it climbs to a 2213 m summit, a net gain of 606 m packed into a distance most riders would consider a warm-up. The thin air near the top only sharpens the difficulty.

How the Gradient Unfolds

The headline figure is the 13.44% average, but averages hide the violence here. The max gradient touches 33.68%, roughly two and a half times the mean, which means there are ramps that force you out of the saddle or off the bike entirely. On a climb this steep the gradient rarely relents into anything you would call recovery — even the "easy" sections sit well into double digits. The gap between the 606 m net gain and the 564 m total ascent is small, confirming that this is an almost relentlessly upward road with no meaningful descending to break the rhythm. Expect the steepest pitches to arrive without much warning, and plan to treat the whole 4.5 km as one sustained effort rather than a series of distinct phases.

Pacing Notes

At an average of 13.44%, gravity dictates your pace far more than fitness does. Your FTP is still the right anchor, but you will spend long stretches above it simply because the gradient leaves no room to soft-pedal. The smart approach is to ride the shallower sections — anything near the average — conservatively so you hold something in reserve for the 33.68% ramps, where power spikes are unavoidable. If you are not sure what your threshold is, run the numbers through the FTP estimator before you commit to a climb like this, because guessing wrong on a 4.5 km wall means blowing up with nowhere to hide.

Gearing

Do not under-gear this climb. A compact 34-tooth chainring paired with a wide cassette is the minimum sensible setup: a 34×32 will get most fit riders up the sustained 13.44% sections, but the moment the road tips toward its 33.68% max you will wish for more. If your derailleur allows it, a 34×34 buys valuable breathing room and lets you keep a survivable cadence on the steepest ramps. For a 606 m gain over just 4.5 km, err on the side of an easier gear — spinning a low ratio beats grinding to a standstill.

Summary

Alto del Bosque is a pure gradient test: short, steep, and unforgiving from bottom to top. Come with the right gears and a disciplined pacing plan, and its 4.5 km will still hurt — but you will reach the 2213 m summit intact.

Length: 4.5 km
Average gradient: 13.44%
Max gradient: 33.68%
Start: 1607 m
Summit: 2213 m
Net gain: 606 m
Total ascent: 564 m
Category: HC