Alto Boquerón

Overview

Alto Boquerón is one of those climbs that stops being a hill and starts being an expedition. It runs for 28.6 km at an average gradient of 7.8%, lifting you from 1726 m at the base all the way to a 3958 m summit. That is a net gain of 2232 m in a single, unbroken effort — and because the road pitches and dips along the way, your legs actually absorb 2364 m of total ascent before the top. It is rated HC, hors catégorie, the hardest classification on the scale, and the numbers make it obvious why.

How the Gradient Unfolds

An average of 7.8% across 28.6 km is relentless on its own, but averages hide the teeth. The maximum gradient touches 25.97% — steep enough that it feels less like pedaling and more like leaning your whole body into the mountain. Expect the profile to swing well above and below the mean: long sustained stretches near the average punctuated by short walls that spike toward that 25.97% figure. The gap between the 2232 m net gain and the 2364 m total ascent tells you there are false descents built into the climb, brief downhill kicks that steal rhythm and force you to rebuild momentum. Treat every dip as a trap, not a rest.

Pacing Notes

At this length, pacing is everything. Nearly all 28.6 km must be ridden below threshold if you want anything left for the steepest ramps. Anchor your effort to your FTP and hold well under it on the sustained sections, saving headroom for the pitches that jump toward 25.97%. If you do not have a recent number to plan around, run the FTP estimator first and build your target power from there. Remember that the summit sits at 3958 m — the thinning air alone will trim your sustainable output the higher you climb, so a pace that feels easy at 1726 m may become your ceiling near the top. Start conservative. The last third of a 2232 m ascent punishes anyone who overcooks the first.

Gearing

Do not under-gear this one. With 28.6 km at 7.8% and ramps at 25.97%, you want the widest range you can bolt on. A compact 34-tooth chainring is the starting point up front. Out back, a 34×32 is the practical minimum for most riders, and it will still leave you grinding on the steepest walls. If you can fit it, a 34×34 gives you the extra rescue gear that keeps your cadence alive when the gradient bites and altitude has already drained your power. On a climb this long, spinning a slightly-too-easy gear beats muscling one that is slightly too hard every single time.

Summary

Alto Boquerón is a genuine high-mountain HC test: 28.6 km, 7.8% average, a 2232 m net rise to 3958 m, and pitches that hit 25.97%. Pace it patiently, gear it generously, and respect the altitude.

Length: 28.6 km
Average gradient: 7.8%
Max gradient: 25.97%
Start: 1726 m
Summit: 3958 m
Net gain: 2232 m
Total ascent: 2364 m
Category: HC