Ōdarumi Pass

Overview

Ōdarumi Pass is a hors catégorie (HC) climb in Japan, and one of the most demanding paved ascents you can tackle in a single push. It runs 21.8 km from a start elevation of 524 m to a summit at 2,358 m, delivering a net elevation gain of 1,834 m. At an average gradient of 8.4%, this is a sustained, high-altitude effort where the finish sits well into the thin air of the high mountains.

The headline net gain understates the real workload. Total ascent on the road is 2,535 m — 701 m more than the net figure. That gap is undulation: rollers, dips, and false flats where you give back altitude and have to re-climb it. Every metre you descend on the way up is a metre you pay for twice, so plan your effort around 2,535 m of climbing, not 1,834 m. On a climb this long, that difference is the margin between finishing strong and blowing up.

How the Gradient Unfolds

The 8.4% average is a blend, not a constant. It hides both recovery sections where you can spin and brutal ramps that spike far above the mean. The 701 m of extra ascent tells you the road does not climb cleanly — it pulses. Expect the gradient to swing hard between shallow and severe, with the steepest pitch hitting 29.47%.

• Flatter and recovery sections where the road eases or briefly descends — use them to eat, drink, and reset your legs.
• Repeated short climbs that stack the extra 701 m of ascent on top of the net gain.
• A steepest ramp of 29.47% that will force you out of any comfortable rhythm and demand your lowest gear.

Pacing Notes

On an undulating HC climb, chase even effort, not even speed. Holding a constant km/h means overcooking the steep ramps and coasting the flats — exactly backwards. Instead, anchor to your sustainable power output and hold a steady target through both the shallow and severe pitches, letting your speed rise and fall with the terrain.

Because 21.8 km at 8.4% is a long day, err below threshold, especially early. If you do not know your numbers, run the FTP estimator before you go and set a ceiling you can actually hold for the full ascent. Bank nothing on the descents — treat the rollers as recovery, not opportunities to attack.

Gearing

The 29.47% maximum pitch dictates your setup. A standard road drivetrain will not turn over on ramps that steep at the top of a 1,834 m climb. Fit a compact or sub-compact chainset paired with a wide-range cassette — something like a 34×32 or 34×34 at minimum — so you keep a cadence that spares your legs and knees. Check your chainset and cassette before the ride; the summit of Ōdarumi Pass is no place to discover you are out of gears.

Summary

• Length: 21.8 km
• Average gradient: 8.4%
• Maximum gradient: 29.47%
• Net elevation gain: 1,834 m
• Total ascent: 2,535 m
• Category: HC

Ōdarumi Pass is a long, steep, high-altitude HC climb where the undulation quietly adds 701 m to your workload. Pace by effort, gear low, and respect the extra ascent hiding behind the net gain.