Coll d'Arnat

Overview

Coll d'Arnat is a category 1 climb that stretches 13.6 km from a start elevation of 567 m to a summit at 1334 m. Over that distance it delivers 767 m of net elevation gain and 781 m of total ascent, and the small gap between those two figures tells you most of what you need to know: this is an honest, relentless climb with barely any respite. At a 5.63% average gradient it never lets the road tilt back downhill for long, and the 14 m difference between net gain and total ascent means only the briefest of false flats interrupt the grind.

Category 1 sits just below the fearsome HC (hors catégorie) rating, so Arnat is among the harder climbs you can tackle. It is long enough to test your endurance and steep enough in places to test your legs, without ever quite reaching the sustained brutality of an HC monster.

How the Gradient Unfolds

The defining number here is consistency. With a 5.63% average across the full 13.6 km, the climb rarely eases off, and the 767 m of net gain arrives in a steady, grinding accumulation rather than a few savage ramps. That said, the 11.44% maximum gradient is roughly double the average, so there are pitches that force you well above your steady rhythm.

Because total ascent (781 m) exceeds net gain (767 m) by only 14 m, you cannot count on descents to recover. What goes up mostly stays up. Expect a climb that settles into a sustained middle section around the average, punctuated by short steeper kicks toward that 11.44% ceiling that demand you shift down and stay seated.

Pacing Notes

On a climb this long and steady, discipline pays. The 5.63% average means Arnat is best ridden as a controlled tempo effort — settle in below your threshold early and hold it. A useful anchor is your FTP: aim to sit comfortably under it for the bulk of the 13.6 km, saving headroom for the pitches that spike toward 11.44%.

If you don't know your threshold, run your numbers through the FTP estimator before you plan the climb. Knowing the figure lets you translate the 767 m of climbing into a repeatable power target rather than riding on feel and blowing up two-thirds of the way up.

The steeper kicks are where riders overcook it. When the gradient jumps from the average toward 11.44%, resist the urge to hold power constant — let your speed drop, spin through, and return to tempo once the ramp relents.

Gearing

For a 13.6 km climb at 5.63% average with ramps to 11.44%, gearing generosity is your friend. A compact 34-tooth inner chainring paired with a 34×32 low gear will get most riders up in comfort, giving you a spin-friendly ratio for the sustained middle section.

If you climb at a lower cadence, carry extra weight, or simply want insurance for the 11.44% pitches near the top of a long day, step up to 34×34. That extra sprocket keeps your legs turning over on the steepest ramps and helps you protect your threshold across the full 767 m of ascent. When in doubt on a category 1 climb of this length, choose the easier gear — a cadence you can hold beats a big gear you can't.

Summary

Coll d'Arnat is a sustained, consistent category 1 test: 13.6 km at 5.63% average with just enough steepness to keep you honest. Ride it as a disciplined tempo effort, gear for the ramps, and let the climb come to you.

Length: 13.6 km
Average gradient: 5.63%
Max gradient: 11.44%
Start: 567 m
Summit: 1334 m
Net gain: 767 m
Total ascent: 781 m
Category: 1