Alto de Siachoque

Overview

Alto de Siachoque is the kind of climb that rearranges your idea of what "hard" means. Over 16.6 km it averages a relentless 9.57%, dragging you from a start elevation of 2411 m up to a summit of 3998 m. That is a net elevation gain of 1587 m, packed into a distance short enough that there is nowhere to hide. With a maximum gradient of 23.34%, it earns its HC (hors catégorie) label without argument — this is the hardest tier a climb can be given, sitting above categories 1, 2, 3, and 4.

The numbers alone tell the story: sustained double-digit average steepness, a summit nearly at 4000 m, and total ascent of 1565 m across a course that never truly flattens. This is a climb of attrition, not tactics.

How the Gradient Unfolds

A 9.57% average across 16.6 km means the road rarely offers relief. Because the net gain (1587 m) is larger than the total ascent (1565 m) is close to it, there are no meaningful descents to reset your legs — nearly every metre of vertical is earned going up. The spikes toward the 23.34% maximum are where the climb bites hardest: these are the pitches that force you out of the saddle and blow apart any rhythm you thought you had.

Expect the shape to be lumpy rather than uniform. When a climb this long averages nearly 10% but tops out above 23%, it means the steepest ramps are punishingly steep, and the "easier" sections are still firmly uphill. Ride it as a series of surges and recoveries, not a single steady effort.

Pacing Notes

At altitudes climbing toward 3998 m, thinning air compounds every percentage point of gradient, so pacing discipline matters more here than almost anywhere. Anchor your effort to your FTP and treat the early kilometres with restraint — going into the red before the first 23%+ ramp will end your day early.

If you do not know your threshold, run the numbers first with the FTP estimator. On a 16.6 km climb averaging 9.57%, aim to hold a wattage you can sustain to the summit, then accept that the steepest pitches will briefly spike you well above it. The goal is to keep those spikes short and recover on the "flatter" 9% sections.

Gearing

Do not under-gear this one. A 9.57% average with ramps to 23.34% will overwhelm anything close to a road-race setup. A compact 34-tooth chainring paired with a wide-range cassette is the minimum sensible choice: 34×32 gives you a fighting chance on the sustained stretches, but for the 23.34% pitches near 3998 m of altitude, 34×34 is the safer bail-out gear. If your frame accepts an even larger sprocket, use it — spinning a low gear beats grinding to a halt.

Summary

Alto de Siachoque is a genuine HC test: long, steep, high, and unforgiving. With 16.6 km at 9.57%, ramps to 23.34%, and a summit just shy of 4000 m, it rewards patience, low gearing, and honest pacing. Respect it early and you can savour the finish; attack it early and it will break you.

Length: 16.6 km
Average gradient: 9.57%
Max gradient: 23.34%
Start: 2411 m
Summit: 3998 m
Net gain: 1587 m
Total ascent: 1565 m
Category: HC