Col de Bionnassay cycling climb profile
The Col de Bionnassay is a long category 1 climb that asks for restraint before it asks for force. On paper, 22 km at 5.38% looks manageable, but the more important number is the 23.51% maximum gradient. That gap between the average and the steepest pitch tells the story: this is not a climb to ride as if the gradient will sit calmly in one place all the way to the top.
The climb starts at 561 m and tops out at 1,745 m, gaining 1,184 m net from bottom to summit. Total ascent is listed at 1,215 m, which means the route is mostly upward but not perfectly smooth in profile. There is enough extra climbing beyond the net gain to suggest minor changes in rhythm, rather than a perfectly metronomic drag.
How the gradient rides
The average gradient of 5.38% makes the climb look aerobic, and for much of the effort that is the correct way to think about it. The problem is that the 22 km length turns even moderate gradients into a durability test. A rider who treats the early kilometres as free speed can end up paying for that choice well before the summit.
The 23.51% maximum is the decisive pacing warning. Even if that steepest section is brief, it changes the gearing and energy-management problem. On a climb with this kind of spread between average and maximum gradient, the sustainable effort is not the same as the speed that feels comfortable on the easier sections. The goal is to preserve enough torque reserve for the steepest ramps without repeatedly spiking above threshold.
Pacing and gearing notes
Pace this as a long threshold-adjacent climb, not as a short hill effort. If using power, anchor the effort to a level you can hold for the full 22 km, then accept that the steepest pitches may briefly push you above that. The key is to avoid making those spikes voluntary. For context on setting that ceiling, see /glossary/ftp.
Gearing should be chosen for the maximum gradient, not the average gradient. A setup that feels fine at 5.38% can become a problem when the road reaches double-digit severity and especially near the listed 23.51% maximum. If cadence collapses there, the climb turns from an endurance effort into a series of strength efforts, and that is rarely the fastest way to manage 1,215 m of total ascent.
Practical approach:
- Start conservatively and let the climb come to you.
- Ride the moderate sections under control rather than chasing speed.
- Shift early before the steepest pitches so cadence does not stall.
- Keep something in reserve until the summit at 1,745 m is realistically close.
The Col de Bionnassay is demanding because the numbers create two different climbs at once: a long aerobic ascent on average, and a much sharper pacing problem whenever the gradient kicks hard. Respect both, and the profile becomes manageable. Ignore the maximum gradient, and the average will be misleading.