Col de Joux

Overview

Col de Joux is an hors catégorie ascent that asks a genuine question of your endurance. Over 20.1 km the road lifts you from 359 m to a summit of 1651 m, an average gradient of 6.42% that never quite lets you settle. The headline numbers are honest: 1292 m of net elevation gain and 1273 m of total ascent, meaning the climb barely gives anything back once it starts pointing upward. There are no long descents built into the profile to break the rhythm — this is a sustained, steady grind rewarded with a ramp to 14.59% at its steepest.

How the Gradient Unfolds

Read the two ascent figures together and the shape becomes clear. Net gain of 1292 m against total ascent of 1273 m tells you the road is almost monotonically upward; the small 19 m difference is all the reprieve the profile offers across the full 20.1 km. That consistency is what makes an average of 6.42% deceptively hard — you rarely get a flat section to spin out your legs and recover.

The 14.59% maximum is more than double the average, so expect the effort to arrive in waves. The steepest pitches are the moments that spike your heart rate and sit you out of the saddle; the surrounding kilometres sit closer to the mean. Plan for the difference between the 6.42% baseline and those 14.59% ramps to be where the climb is won or lost.

Pacing Notes

At this length, discipline beats bravado. On a climb of 20.1 km, the smartest riders hold a steady effort just under threshold and refuse to chase early. Your FTP is the number to anchor to — target a wattage you can sustain for the better part of an hour, then protect it. If you do not know your threshold yet, run the numbers through the FTP estimator before you commit to a pacing plan.

The key discipline is riding the average, not the ramps. When the gradient jumps toward 14.59%, let your speed drop and your cadence do the absorbing rather than punching over each pitch. Spending too much above threshold early on a 1292 m climb is the fastest way to blow with the summit at 1651 m still out of sight.

Gearing

For an HC climb of this length and steepness, gear low and gear early. A compact 34-tooth chainring is the baseline, and the question is how much cassette you pair with it. A 34×32 is the minimum I would bring for the 14.59% sections — enough to keep cadence up when the road bites, provided your threshold is strong. Most riders will be happier on a 34×34, which buys a little more spin on the steepest ramps and keeps your legs fresher across the full 20.1 km. If you tend to grind, err toward the 34×34; the extra range costs nothing on the shallower stretches and saves you when the gradient spikes.

Summary

Col de Joux is a proper HC test: long, consistent, and steep in the right places. Pace it by the average, save something for the 14.59% ramps, and gear low enough to keep spinning to the top.

Length: 20.1 km
Average gradient: 6.42%
Max gradient: 14.59%
Start: 359 m
Summit: 1651 m
Net gain: 1292 m
Total ascent: 1273 m
Category: HC