Alto de los Tunjos

Overview

Alto de los Tunjos is a genuine hors-catégorie test of endurance. At 36.2 km long it is not a climb you attack — it is one you survive, ration, and eventually outlast. From a base at 1516 m the road grinds all the way to 3801 m, a summit high enough that the thinning air becomes a second climb layered on top of the first. The net elevation gain is 2285 m, with a total ascent of 2268 m once you account for the handful of flatter and gently descending stretches folded into its length.

The average gradient of 6.32% sounds almost civilised. It is not. Over 36.2 km that average adds up relentlessly, and it hides a maximum pitch of 19.82% that can crack even a well-managed ride if you meet it with tired legs.

How the Gradient Unfolds

Think of this climb in terms of shape rather than switchback-by-switchback detail. A 6.32% average across 36.2 km means the road rarely lets up, but it is not perfectly even. The gap between the 2285 m net gain and the 2268 m total ascent tells you there are brief reprieves — short kickers of descent or false-flat where you can breathe, drink, and reset.

The danger sign is that 19.82% maximum. A ramp nearly three times steeper than the average will appear when your reserves are lowest. Treat every steep pitch as a spike above a long, grinding baseline, and never let the "gentle" average lull you into spending too early.

Pacing Notes

On a climb this long, pacing is everything. The single biggest mistake is riding the early kilometres by feel — at 1516 m the air is still generous and your legs feel strong, which is exactly the trap. Anchor your effort to power, not sensation.

Ride the bulk of the 36.2 km at or just below your FTP, holding a steady sustainable output rather than chasing the gradient. As you climb past 3000 m toward the 3801 m summit, expect your ceiling to fall with the altitude, so build in a mental deduction for the final third. If you don't know your threshold, run the numbers through the FTP estimator before you commit to a target — a climb of 2285 m of gain punishes a guess badly. Save something specific for the 19.82% ramps so you can absorb them without redlining.

Gearing

Gear for the worst pitch, not the average. A compact 34-tooth chainring paired with a 32-tooth cassette sprocket (34×32) is the sensible floor here, and on a 36.2 km climb reaching 19.82% many riders will be far happier dropping to a 34×34. The lower ratio keeps your cadence spinning on the steepest ramps and, critically, protects your legs across the sheer duration to the 3801 m summit. If your bike accepts a wide-range cassette, take it — spinning a slightly-too-easy gear costs nothing, while grinding a too-hard one late in a 2285 m ascent can end your day.

Summary

Alto de los Tunjos is a long-haul HC climb defined by its length and altitude as much as its slope. Pace it on power, gear it generously, and respect the summit air.

Length: 36.2 km
Average gradient: 6.32%
Max gradient: 19.82%
Start: 1516 m
Summit: 3801 m
Net gain: 2285 m
Total ascent: 2268 m
Category: HC