Alto de Sucubún

Overview

Alto de Sucubún is a hors catégorie climb that gives you nowhere to hide. Across 12.2 km it averages 9.9%, and the summit sits at 3453 m — high enough that thin air stacks on top of an already punishing gradient. From the 2242 m start you gain 1211 m of net elevation, with a total ascent of 1194 m along the way. That average alone would define most HC efforts; here it's paired with altitude, which is why this climb earns the top rating.

How the Gradient Unfolds

The headline number is the 9.9% average, but averages flatten the story. With a maximum of 24.62%, this road delivers ramps more than twice as steep as its mean. Expect the gradient to swing hard: stretches that sit near the 9.9% line, then abrupt walls that spike toward that 24.62% figure. Because the net gain (1211 m) exceeds the total ascent (1194 m) only marginally, there's virtually no respite — almost every metre you climb stays climbed. There are no meaningful descents to recover on. Over 12.2 km, that consistency is what grinds riders down: the road simply keeps pointing up, and the steepest pitches arrive without the flat run-ins that would let you carry speed into them.

Pacing Notes

On a climb this long and steep, pacing is everything. Anchor your effort to a percentage of your FTP and hold it — going into the red on an early 24.62% ramp will cost you dearly over the remaining kilometres. If you don't know your threshold, run the numbers through the FTP estimator first, then set a target you can sustain for the full 12.2 km rather than the first two.

Because the summit reaches 3453 m, factor in altitude: the higher you climb above the 2242 m start, the more the same power will cost you in perceived effort. Ride the steady 9.9% sections conservatively and treat the walls toward 24.62% as brief surges to survive, not attacks to launch. Save something — the climb only ends at the very top.

Gearing

Gear for the maximum, not the average. A 34×32 is the sensible floor here, and on a 9.9% average stretching to 12.2 km many riders will be grateful for the extra range of a 34×34. If your legs or your altitude tolerance are in question, err toward the easier ratio: on pitches approaching 24.62%, a bailout gear keeps your cadence alive and your knees intact. Spinning a 34×34 up the steep ramps beats grinding a 34×32 into the ground. Choose the gearing that lets you hold your target effort all the way to 3453 m.

Summary

Alto de Sucubún is a genuine HC test: 12.2 km, a relentless 9.9% average, and walls to 24.62%, delivered at altitude between 2242 m and 3453 m. Pace it to your threshold, gear low, and respect the 1211 m of vertical ahead of you.

Length: 12.2 km
Average gradient: 9.9%
Max gradient: 24.62%
Start: 2242 m
Summit: 3453 m
Net gain: 1211 m
Total ascent: 1194 m
Category: HC