Colletto Serasin

Overview

Colletto Serasin is a long, category 1 haul that rewards patience over power. Over 23.9 km the road lifts you from 796 m at the base to a 2174 m summit, a net gain of 1378 m. The average gradient reads a deceptively civil 5.76%, but averages flatten the story: with a max pitch of 39.17%, this climb hides at least one wall that will empty your legs in seconds. The total ascent of 1347 m sits just under the net figure, telling you the road climbs almost continuously with only the smallest concessions of respite.

How the Gradient Unfolds

Do the math and the 5.76% average feels manageable, but the shape is what defines Colletto Serasin. A climb this long — nearly 24 km — that still lands only a single category below the hardest tier owes its rating to length as much as steepness. Because the total ascent (1347 m) is 31 m shy of the net elevation gain (1378 m), the profile is overwhelmingly uphill with almost no descending stretches to break rhythm. The headline number is that 39.17% maximum. Even if that spike is brief, it forces you to arrive with reserves intact. Everything above and below it will feel gentle by comparison, which is exactly the trap: burn matches early and the back half of the 23.9 km becomes a survival exercise.

Pacing Notes

On a climb of this duration, discipline beats bravado. Your FTP is the anchor here: settle into a sustainable percentage of it and hold it, rather than chasing the gradient. Because Colletto Serasin runs 23.9 km, even small over-efforts compound into a blown effort long before the 2174 m summit. Sit slightly below threshold on the steady 5.76% stretches and save your surplus for the 39.17% pitch, where you will have no choice but to spike hard for a short burst. If you do not know your threshold, run the numbers through the FTP estimator first so your target watts are grounded in data, not guesswork. Aim to crest with something left rather than pacing to the point of cracking.

Gearing

Length plus a 39.17% spike means gearing is not optional — it is the difference between riding and walking. For most riders a compact 34-tooth chainring paired with a wide cassette is the sensible baseline. A 34×32 will carry you through the sustained 5.76% grades comfortably, but the max pitch argues strongly for going lower still. A 34×34 gives you a genuine bailout ratio for that wall, letting you keep the pedals turning where a tighter setup would stall you. Given the 1378 m of climbing ahead, err toward the easier gear; spinning a low ratio over 23.9 km preserves the legs far better than grinding.

Summary

Colletto Serasin is a test of endurance and pacing, a long category 1 climb whose 5.76% average masks a brutal 39.17% surprise. Gear low, pace to your threshold, and respect the full 23.9 km.

Length: 23.9 km
Average gradient: 5.76%
Max gradient: 39.17%
Start: 796 m
Summit: 2174 m
Net gain: 1378 m
Total ascent: 1347 m
Category: 1