Col de la Glière

Overview

The Col de la Glière is a genuine hors catégorie (HC) test, the kind of climb that rewards patience and punishes ambition. Over 29.7 km it lifts you from a start elevation of 596 m to a summit at 2475 m, an average gradient of 6.34% that never quite lets you settle. The net elevation gain is 1879 m, but the total ascent adds up to 1923 m — a 44 m difference that tells you the road is not a single clean ramp. There are dips, false flats, and short recoveries folded into the profile, and each one steals a little rhythm before the road tilts up again.

At nearly thirty kilometres, this is an effort measured in fractions of an hour, not minutes. The scale alone puts it in rarefied company: very few paved climbs stack up 1923 m of climbing in one continuous push to a summit this high.

How the Gradient Unfolds

A 6.34% average across 29.7 km is deceptive. The 44 m gap between the 1879 m net gain and the 1923 m total ascent means the climb gives back a little altitude here and there — every metre you descend mid-climb is a metre you have to reclaim, always at more than the headline gradient. Expect the effective steepness of the true climbing sections to sit noticeably above 6.34% to compensate for those give-backs.

Practically, treat the profile as a long, uneven staircase rather than a smooth wall. The upper reaches, pushing toward 2475 m, combine gradient with thinning air, so the final third feels harder than the raw percentage suggests even where the road eases.

Pacing Notes

On a climb this long, pacing is everything. Anchor your effort to a percentage of your FTP and hold it — the temptation to chase the early ramps is what blows the back half apart. For most riders, a sustainable target of roughly 70–80% of FTP over 29.7 km keeps you out of the red while the altitude climbs toward 2475 m.

If you are unsure of your current threshold, run the numbers through the FTP estimator before you commit to a target. Ride the recoveries where the profile dips — those 44 m of give-back are free rests if you stay relaxed rather than surging.

Gearing

With 1923 m of ascent and long stretches above the 6.34% average, gear low and gear early. A compact 34-tooth inner ring paired with a wide-range cassette is the sensible baseline. A 34×32 will get most fit riders to the 2475 m summit, but on the steeper reclaimed pitches — where the effective gradient runs well over 6.34% — you will be grateful for a 34×34. If your legs are unproven over 29.7 km at altitude, fit the 34×34 and spin; a high cadence protects your legs for the final kilometres far better than grinding does.

Summary

The Col de la Glière is a full-value HC climb: nearly thirty kilometres, a summit near two and a half thousand metres, and a total ascent that rewards disciplined pacing and low gearing. Respect the distance, mind the give-backs, and let the mountain come to you.

Length: 29.7 km
Average gradient: 6.34%
Max gradient: n/a
Start: 596 m
Summit: 2475 m
Net gain: 1879 m
Total ascent: 1923 m
Category: HC