Coll de Siern

Overview

Coll de Siern is a Category 1 climb in Spain covering 10.6 km. Over that distance it delivers a net elevation gain of 889 m, starting at 737 m and topping out at a summit of 1626 m. The average gradient across the full ascent sits at 8.36%, which places it firmly in the range where sustained climbing form matters more than raw punch.

The number that reshapes how you ride this climb is the gap between net gain and total ascent. You net 889 m, but you actually climb 1236 m — a difference of 347 m. That extra 347 m is descending and re-climbing hidden inside the profile. It means Coll de Siern is not a clean, one-directional drag: you pay for elevation you then give back, and pay for it again. Budget your effort for 1236 m of climbing, not 889.

How the Gradient Unfolds

An 8.36% average on an undulating climb is deceptive. Because 347 m of the ascent is offset by descents and flats, the pitches that do climb are steeper than the average implies. Expect the road to swing between genuine ramps and short recovery sections rather than holding one steady grade.

• Flatter and downhill sections where you recover and carry speed
• Repeated short climbs that reset your legs each time you settle
• Steeper ramps well above 8.36% where the real work concentrates

Pacing Notes

On a climb this lumpy, chasing an even speed will blow you up. Every time the road pitches, holding the same pace forces a surge; every descent tempts you to coast and lose rhythm. Instead, pace to even effort — hold a steady sustainable power output through the ramps and let your speed rise on the flatter, descending sections rather than pushing to keep the number climbing.

Practically: ride the steep pitches at or just below threshold, then use the 347 m of give-back terrain to spin and clear the legs. If you do not know your threshold, run the FTP estimator first so your effort target is real, not a guess.

Gearing

The steep ramps on Coll de Siern reward gearing that lets you keep cadence when the grade bites well past the 8.36% average. Fit a compact or sub-compact chainset paired with a wide-range cassette — a 34×32 or 34×34 combination gives you the low end to spin the ramps instead of grinding them. Check your setup before the ride; discovering you are over-geared halfway up an undulating Cat 1 is a long, slow lesson.

Summary

• Length: 10.6 km
• Average gradient: 8.36%
• Net elevation gain: 889 m
• Total ascent: 1236 m
• Category: 1

Coll de Siern reads harder on the road than its net gain suggests. Respect the full 1236 m of ascent, pace to effort through the undulation, gear low, and it becomes a climb you finish strong rather than survive.