Collado de Serranillos

Overview

Collado de Serranillos is a Category 1 climb in Spain, running 13.3 km from a start elevation of 622 m to a summit at 1,460 m. Its net elevation gain is 838 m, and the road averages 6.29% across the ascent. Those numbers put it firmly in the range where the climb rewards steady, sustained work rather than a hard start.

The key detail is the gap between net elevation gain and total ascent. You climb 838 m in net terms, but the total ascent is 1,266 m — a difference of 428 m. That extra vertical is climbing you do and then give back, which means the profile undulates rather than rising cleanly. Practically, you pay for more altitude than the summit height alone suggests, and the descents between pitches interrupt your rhythm without offering much real recovery.

How the Gradient Unfolds

The 6.29% average is a blended figure that hides both easier valleys and sharp ramps. With 428 m of extra ascent baked into the profile, the road repeatedly kicks up, eases, and kicks again rather than holding one steady grade. Expect the hardest sections to sit well above the average.

• Flatter or descending sections where you recover briefly and can shift up
• Repeated short climbs that force you back onto the pedals after each dip
• A steep ramp noticeably harder than the 6.29% average, where the grade bites

Pacing Notes

On a climb this undulating, even-effort beats even-speed. Chasing a constant speed forces you to spike hard on every ramp and coast on every dip, burning matches you cannot get back. Instead, hold a steady sustainable power output and let your speed rise and fall with the terrain — faster on the shallow sections, slower on the steep ones, but with your effort roughly level throughout.

Before the ride, pin down your numbers with the FTP estimator. Knowing your ceiling keeps you from over-cooking the first ramp with 13.3 km still to climb and 1,266 m of total ascent in your legs.

Gearing

Gear for the steepest ramp, not the average. On a Category 1 climb with sharp pitches well above 6.29%, a compact (50/34) or sub-compact chainset paired with a wide-range cassette gives you the low gears to spin the hard sections without grinding. A 34×32 or 34×34 combination lets you keep cadence up when the grade bites. Check your setup before the ride — swapping a cassette at the roadside is not an option.

Summary

• Length: 13.3 km
• Average gradient: 6.29%
• Net elevation gain: 838 m
• Total ascent: 1,266 m
• Category: 1

Collado de Serranillos is a genuine Category 1 test: 13.3 km at 6.29% on paper, but 1,266 m of total ascent underneath. Ride it on even effort, gear low for the ramps, and respect the undulation that makes it harder than the net figures suggest.