Col de Bonneval / Colle sud di Bonnevalle

Overview

The Col de Bonneval, known on its Italian side as the Colle sud di Bonnevalle, is a genuine hors catégorie test — the hardest classification on the scale before you drop down to categories 1, 2, 3, and 4. It runs for 24.3 km from a valley floor at 476 m up to a summit of 2090 m, a net gain of 1614 m. The average gradient sits at 6.64%, which sounds civilized until you remember it is sustained across nearly a marathon's worth of climbing. This is an endurance climb first and a steepness climb second: the length is what breaks people, not any single wall.

How the Gradient Unfolds

At 24.3 km with a 6.64% average, the Bonneval never really lets you coast. The total ascent of 1604 m is only marginally less than the net gain of 1614 m, which tells you almost the entire road points relentlessly upward — there are no meaningful descents or false-flat reprieves to recover on. The pitch does spike, with a maximum gradient of 14.04% that is more than double the average. Expect the profile to hover in the mid-single digits for long stretches, then bite hard on the steeper ramps where the road tips toward that 14.04% figure. Because the climb tops out at 2090 m, the upper reaches also thin the air, so those late steep sections feel harsher than the same gradient would lower down.

Pacing Notes

On a climb this long, discipline beats bravado. The single biggest mistake is chasing the early kilometers and paying for it across the remaining distance. Anchor your effort to your FTP and aim to ride the sustained sections just below threshold, saving matches for the ramps toward 14.04%. If you do not have a recent number, run the FTP estimator before you go so your target power is honest rather than hopeful. Over 24.3 km of gaining 1614 m, a rider who sits patiently at a repeatable intensity will pass the rider who surged early. Fuel and drink continuously — the summit at 2090 m is a long time coming.

Gearing

Do not under-gear this one. With a 6.64% average stretched over 24.3 km and pitches to 14.04%, you want a bailout that lets you keep a comfortable cadence when the road bites. A compact 34-tooth chainring paired with a 34×32 low gear is a sensible baseline for strong riders. If you are carrying luggage, tiring late in a long day, or simply want to protect your legs across all 1614 m of ascent, step up to 34×34. The extra range costs nothing on the flats and buys you spin instead of grind when you are deep into the climb at altitude.

Summary

The Col de Bonneval / Colle sud di Bonnevalle is a patient, punishing HC climb: long, unrelenting, and topped by thin air at 2090 m. Pace it by the numbers, gear low, and let the length do the talking.

Length: 24.3 km
Average gradient: 6.64%
Max gradient: 14.04%
Start: 476 m
Summit: 2090 m
Net gain: 1614 m
Total ascent: 1604 m
Category: HC