Col de la Bonette

Overview

The Col de la Bonette is a hors catégorie effort, the hardest rating on the scale before you drop to categories 1, 2, 3, and 4. Over 12.4 km it averages 8.72%, dragging you from a start elevation of 1618 m to a summit at 2703 m. That is 1085 m of net vertical gain, and with dips and false flats folded in, the total ascent tallies 1450 m — meaning roughly 365 m of climbing beyond the straight-line rise is spent regaining ground you briefly gave back.

What sets Bonette apart is not just the numbers but where they sit. A start above 1600 m and a finish past 2700 m means the entire climb happens in thin, cold air, and every watt costs more than it would at sea level. This is a climb of altitude as much as gradient.

How the Gradient Unfolds

An 8.72% average across 12.4 km is brutally consistent, but the gap between the 1085 m net gain and the 1450 m total ascent tells you the road is not a clean ramp. Those extra 365 m of ascent come from short descents and flatter recovery sections woven into the climb — each one a small gift that you pay back with steeper pitches elsewhere.

Read this shape carefully. Because the average is pulled down by the flatter and downhill stretches, the climbing sections that remain must exceed 8.72% to compensate. Expect walls that bite harder than the headline number, punctuated by brief eases where you can breathe before the road tilts up again. The final approach to 2703 m is where thin air compounds the gradient most.

Pacing Notes

On a climb this long and this high, the single biggest mistake is starting too hard. Anchor your effort to your FTP and hold something sustainable — the altitude alone will erode your ceiling as you climb, so a wattage that feels easy at 1618 m may feel far harder near 2703 m.

If you are not sure what your FTP is, run the numbers through the FTP estimator before you commit to a target. Use the flatter recovery stretches — the ones responsible for the 365 m gap between net gain and total ascent — to soft-pedal and drop your heart rate, then settle back into rhythm on the steep pitches rather than attacking them. Steady is fast here.

Gearing

With a 12.4 km climb averaging 8.72% and pitches that run steeper still, gear low and gear early. A compact 34-tooth chainring paired with a 34×32 gives most riders enough range to spin the sustained sections without grinding. If you carry any fatigue, ride at a lower FTP, or simply want insurance for the steepest ramps near the 2703 m summit, drop to a 34×34 for that extra margin. At this altitude, protecting your cadence matters more than saving a few grams — err toward the easier ratio.

Summary

The Col de la Bonette rewards patience: 12.4 km at 8.72%, entirely in high, thin air, climbing from 1618 m to 2703 m. Respect the altitude, pace to your FTP, gear low, and let the flatter sections give you back what the walls take.

Length: 12.4 km
Average gradient: 8.72%
Max gradient: n/a
Start: 1618 m
Summit: 2703 m
Net gain: 1085 m
Total ascent: 1450 m
Category: HC