Portillo de la Sía

Overview

Portillo de la Sía is a long, category 1 ascent that rewards patience over punch. Over 18.8 km the road lifts you from a valley floor at 162 m to a summit at 1236 m, a net gain of 1074 m. The average gradient of 5.72% sounds moderate, and for much of the climb it genuinely is — but at this length, a "moderate" average still adds up to a serious day. The recorded total ascent of 1063 m confirms that this is a mostly relentless drag upward, with little in the way of descending or flat relief to break the rhythm.

How the Gradient Unfolds

The number to respect here is the spread between the 5.72% average and the 10.52% maximum. That gap tells you the climb is not perfectly even: alongside long stretches near the average, there are pitches that nearly double it. On an 18.8 km climb, those steeper ramps arrive when your legs are already deep into the effort, so they feel harder than the raw 10.52% figure suggests.

Because the net gain (1074 m) and total ascent (1063 m) are almost identical, you can assume the road climbs continuously without meaningful downhill. Plan for a sustained grind rather than a series of discrete walls, and treat every ramp toward the 10.52% max as a moment to sit down, hold form, and let the gradient ease again.

Pacing Notes

At nearly 19 km, this climb is won by pacing, not heroics. Anchor your effort to your FTP: riding the bulk of the ascent just below threshold keeps you sustainable across a climb that will likely take most riders well over an hour. Going into the red on the early slopes is the classic mistake — with 1074 m still to gain, there is no room to recover from an over-cooked start.

If you're unsure of your threshold, run the numbers through the FTP estimator first, then set a target power you can hold from bottom to top. On the steeper pitches toward 10.52%, let your power spike briefly rather than surge, and settle straight back to your average-gradient rhythm once the road relents.

Gearing

Given the 18.8 km length and a 5.72% average that repeatedly ramps toward 10.52%, gear for the long haul rather than the short surge. A 34×32 is a sensible baseline for strong climbers who can hold a steady cadence at threshold. But because the climb keeps pitching upward when fatigue is highest, most riders will be glad of a 34×34 — that extra sprocket lets you keep spinning through the max-gradient ramps instead of grinding to a standstill. When in doubt on a climb this sustained, choose the easier option.

Summary

Portillo de la Sía is a classic long-and-steady category 1 test: 18.8 km, a 5.72% average that hides ramps to 10.52%, and 1074 m of vertical to conquer. Pace it off your threshold, gear generously, and let the climb come to you.

Length: 18.8 km
Average gradient: 5.72%
Max gradient: 10.52%
Start: 162 m
Summit: 1236 m
Net gain: 1074 m
Total ascent: 1063 m
Category: 1