Colle dell'Assietta

Overview

Colle dell'Assietta is an hors catégorie monster, the kind of climb that rewrites your sense of how long a day in the saddle can be. At 41.2 km, it is less a single ascent than an expedition: you leave the valley floor at 455 m and grind all the way up to a summit of 2570 m. That is 2115 m of net elevation gain, with 2154 m of total ascent once the small dips and false flats are counted. The average gradient reads a deceptively civil 5.14%, but averaged across more than forty kilometres, that number hides enormous variation — including a wall that spikes to 20.1%. This is a climb of patience first and power second, and its HC rating is fully earned by sheer duration and the thin air near the top.

How the Gradient Unfolds

The story of the Assietta is the story of its inconsistency. A 5.14% mean over 41.2 km tells you the climb never settles into a rhythm you can lock onto for long. Expect long stretches that sit well below average — shallow drags and even the occasional respite — offset by punchier sections that drive the number back up. The defining feature is that 20.1% maximum: a gradient nearly four times the average, and the single moment where any pacing plan can unravel. Because the summit sits at 2570 m, the final kilometres also come at altitude, where the same wattage buys noticeably less speed. Read the climb in blocks rather than as one continuous effort, and treat every steep pitch as its own small crisis to manage.

Pacing Notes

On a climb this long, discipline near your FTP is everything. Riding even slightly over threshold on the early ramps compounds into a blow-up long before the summit at 2570 m. Aim to spend the bulk of the 41.2 km comfortably below threshold, saving your matches for the steep pitches — especially anything approaching that 20.1% wall, where you will briefly go well over FTP whether you like it or not. If you do not know your threshold precisely, calibrate it first with the FTP estimator so your target power reflects reality rather than optimism. Factor in the altitude too: aerobic ceiling drops as you climb toward 2570 m, so the effort that felt sustainable at 455 m will feel harder up high.

Gearing

With 41.2 km of climbing, 2115 m to gain, and a 20.1% maximum, gear low and gear generously. A compact 34-tooth chainring is the sensible front end. Pair it with at least a 34×32 for the sustained shallower drags, but given the length and that brutal 20.1% ramp, a 34×34 is the safer choice — the extra range keeps your cadence alive when the road stands up and your legs are already deep into 2154 m of accumulated ascent.

Summary

Colle dell'Assietta is a full-day HC test: 41.2 km, a summit at 2570 m, and 2115 m of net climbing that demand patience, pacing, and generous gearing.

Length: 41.2 km
Average gradient: 5.14%
Max gradient: 20.1%
Start: 455 m
Summit: 2570 m
Net gain: 2115 m
Total ascent: 2154 m
Category: HC