Passo del Busan

Overview

Passo del Busan is an hors catégorie monster, and the length alone tells you most of what you need to know: 25.8 km of continuous climbing. From a valley floor at 224 m it winds all the way up to a summit at 1813 m, a net elevation gain of 1589 m. The average gradient reads 6.15%, which sounds civilised on paper — but averages lie on a climb this long. With a total ascent of 1632 m logged across the profile, there are short pitches of descent and false flat baked in, meaning the climbing sections are steeper than the headline figure suggests.

How the Gradient Unfolds

Do the arithmetic and the shape reveals itself. Total ascent of 1632 m against a net gain of 1589 m means roughly 43 m of the climb is spent going the wrong way, giving up altitude you then have to reclaim. Over 25.8 km, a 6.15% average is relentless but rideable — until it isn't. The max gradient of 34.71% is the sting in the tail of this profile: a wall so steep it belongs in a different category of riding entirely, where staying upright and keeping the front wheel down matters as much as power. Expect the road to breathe — stretches near the average punctuated by savage kicks that spike far above 6.15%, so that the effort never settles into a rhythm you can switch off inside.

Pacing Notes

On a climb of 25.8 km, discipline beats bravado. The single biggest mistake is riding the opening kilometres at a pace the summit at 1813 m will never forgive. Anchor your effort to your FTP and hold something in reserve for the ramps — including that 34.71% wall — rather than chasing a fast split early. If you don't know your threshold, run the numbers through the FTP estimator before you commit to a target. As a rough plan: sit slightly below threshold on the sustained 6.15% sections, then accept that the steepest pitches will punch you well over it for short bursts. The 1589 m of net gain is a long time to be climbing, so ride the average and survive the spikes.

Gearing

Come prepared. For most riders tackling an HC climb of this length, a compact 34-tooth chainring is the starting point. Pair it with at least a 34×32 for the sustained 6.15% grind — that's the bailout most amateurs will want across 25.8 km. But the 34.71% max gradient argues for more: a 34×34 gives you a genuine crawler gear for the wall, keeping your cadence turning when the road stands up. If your frame and derailleur can accommodate it, err toward the 34×34. Spinning a low gear costs nothing on the flatter false-flat sections and saves your legs for the top.

Summary

Passo del Busan earns its HC rating honestly: long, steep, and topped by a gradient that borders on absurd. Come with low gears, a patient plan, and respect for all 1589 m of vertical between you and the summit.

Length: 25.8 km
Average gradient: 6.15%
Max gradient: 34.71%
Start: 224 m
Summit: 1813 m
Net gain: 1589 m
Total ascent: 1632 m
Category: HC