Alto de los Rayos

Overview

Alto de los Rayos is a hors catégorie (HC) climb that offers no hiding place. Over 17.8 km it averages 9.1%, gaining a net 1617 m as the road lifts from 1107 m at the base to a 2724 m summit. With a total ascent of 1598 m logged across the effort, almost every meter of forward progress is also a meter of altitude. This is not a climb with false flats to recover on — the average alone would rank it among the steepest long ascents anywhere, and the 18.34% max gradient confirms it bites hard where it wants to.

How the Gradient Unfolds

The defining number here is consistency. A 9.1% average sustained across 17.8 km means the climb rarely relents; where many long ascents dilute their difficulty with flatter middle sections, Rayos holds its pitch. The gap between the net gain of 1617 m and the total ascent of 1598 m is tiny — just 19 m — which tells you there is almost no descending or leveling once you start. What variation exists comes in the ramps: sections spiking toward the 18.34% max sit well above the average, so expect the grade to lurch from hard to brutal rather than hard to easy. Treat every steeper pitch as a surge you must absorb, then settle back onto the punishing baseline.

Pacing Notes

On a climb this long and steep, pacing discipline decides everything. Riding at or just below your sustainable threshold is essential — anchor your effort to your FTP and resist the urge to chase the early ramps. At 17.8 km, an over-eager first third will cost you far more in the final kilometers than it buys you at the base. If you are unsure of your number, run it through the FTP estimator before you commit to a target power. Because the summit sits at 2724 m, thinner air late in the climb will quietly erode the power you had at 1107 m, so build a small margin into your pacing plan and expect the last stretch to feel harder than the gradient alone suggests.

Gearing

Gear for survival, not pride. With a 9.1% average and ramps to 18.34%, a compact 34-tooth inner ring paired with a wide cassette is the sensible baseline. A 34×32 will get most fit riders up the steady sections, but on the steepest pitches — and after more than an hour of climbing — that ratio can leave you grinding below a healthy cadence. Fitting a 34×34 buys you a meaningful extra margin, letting you spin rather than muscle through the 18.34% walls. Given the sustained nature of the ascent, err toward the easier setup; the ability to keep your legs turning over 17.8 km matters more than a slightly higher top gear you will rarely use.

Summary

Alto de los Rayos is a pure test of sustained climbing: long, uniformly steep, and topping out high enough that altitude becomes a factor. Pace to your threshold, gear low, and respect the 18.34% ramps.

Length: 17.8 km
Average gradient: 9.1%
Max gradient: 18.34%
Start: 1107 m
Summit: 2724 m
Net gain: 1617 m
Total ascent: 1598 m
Category: HC