Alto de Rio

Overview

Alto de Rio is a genuine giant. Over 43.8 km it climbs at an average of 5.24%, dragging you from a start elevation of 553 m all the way to a 2849 m summit. That is a net elevation gain of 2296 m, and with the rolling in-between sections factored in, a total ascent of 2674 m. Classified HC — hors catégorie, the hardest rating there is, above categories 1, 2, 3, and 4 — this is a climb measured in hours, not minutes. The moderate-sounding average hides a max gradient of 21.09%, so treat the headline number with respect: it is a mean across nearly 44 kilometres, not a promise of an easy grade.

How the Gradient Unfolds

A 5.24% average across 43.8 km tells you this is a long haul rather than a wall, but the 21.09% max gradient means the mean is doing a lot of smoothing. Expect the profile to breathe: flatter, almost recovery-paced kilometres offset the pitches that spike far above average. The gap between the 2296 m net gain and the 2674 m total ascent — a difference of 378 m — confirms there are descents and false flats woven in, meaning you will occasionally give back altitude only to reclaim it. The final push toward 2849 m happens in thinning air, where every percent of gradient feels heavier than it reads.

Pacing Notes

On a climb this long, discipline beats bravado. Anchor your effort to a percentage of your FTP and hold it, especially through the early kilometres when fresh legs tempt you to overspend. With 43.8 km ahead, going even slightly too hard in the first hour can cost you dearly near the 2849 m summit. If you are unsure of your threshold, run the numbers through the FTP estimator first, then set a target you can sustain for the full duration. Save something for the steepest ramps toward that 21.09% max, and don't let the flatter recovery sections lull you into complacency — they are where you eat, drink, and reset for the next pitch.

Gearing

At HC length and altitude, gearing is survival, not vanity. A compact 34-tooth chainring paired with a wide-range cassette is the sensible baseline. A 34×32 will get most fit riders up the sustained 5.24% stretches, but given the 21.09% max gradient and the fatigue that builds across 43.8 km, a 34×34 gives you the extra bailout for those spikes and for the thin-air kilometres near 2849 m. If your bike accepts it, err toward the easier ratio — spinning a cadence you can hold for hours is far kinder than grinding a gear you'll come to regret.

Summary

Alto de Rio is a full-day HC test: long, high, and deceptively varied. Pace it to your threshold, gear it low, and respect the 2296 m of altitude you must earn.

Length: 43.8 km
Average gradient: 5.24%
Max gradient: 21.09%
Start: 553 m
Summit: 2849 m
Net gain: 2296 m
Total ascent: 2674 m
Category: HC