Forcella della Lavina / Klanška škrbina

Overview

Forcella della Lavina, known on the Slovenian side as Klanška škrbina, is a genuine hors catégorie climb — the hardest classification a road ascent can carry. Over 12.5 km it drags you from a start elevation of 583 m up to a summit at 1841 m, a net gain of 1258 m. The average gradient reads 10.08%, and that number alone tells the story: there is almost nowhere to recover. Sustaining double digits for the better part of an hour puts this climb among the most punishing you can attempt on a road bike.

How the Gradient Unfolds

Numbers rarely lie, and here they paint a wall. An average of 10.08% across 12.5 km means the climb barely dips below that figure at any point; the flatter stretches that usually let riders breathe simply do not exist in meaningful quantity. The recorded max gradient of 17.8% marks the cruelest ramp — nearly 8 percentage points above an already brutal average. Expect the road to pitch up steeply early and stay there, with the steepest sections biting hardest where fatigue has already set in. The gap between the net elevation gain of 1258 m and the total ascent of 1223 m is small, confirming the road climbs relentlessly upward with little in the way of downhill relief along the way.

Pacing Notes

On a climb this steep and this long, pacing discipline is everything. Anchor your effort to your FTP and resist the temptation to chase the early ramps — burning matches in the first few kilometres of a 12.5 km, 10.08% climb is a one-way ticket to blowing up before the summit. Aim to hold a steady, sustainable power just below threshold and let the gradient dictate cadence rather than forcing pace. Because the road so rarely eases, there are few natural spots to soft-pedal and recover, so your effort needs to be even from the base. If you are unsure of your threshold number before tackling it, run the numbers through the FTP estimator first and build your target around a figure you can actually hold for the full ascent to 1841 m.

Gearing

Do not underestimate the gearing you need here. A 10.08% average with pitches to 17.8% will overwhelm anything too tall. A compact 34-tooth chainring paired with a wide-range cassette is the sensible baseline. A 34×32 gives most fit riders enough to spin the sustained sections, but on the 17.8% ramps — especially deep into the 1258 m of climbing — many riders will be grateful for a 34×34 or lower. If your legs or your fitness are in any doubt, gear easier than you think you need. Preserving cadence on a wall like this saves your legs for the summit.

Summary

Forcella della Lavina / Klanška škrbina is a true HC test: long, staggeringly steep, and unforgiving from base to summit. Respect the 10.08% average, gear generously, and pace with your threshold in mind.

Length: 12.5 km
Average gradient: 10.08%
Max gradient: 17.8%
Start: 583 m
Summit: 1841 m
Net gain: 1258 m
Total ascent: 1223 m
Category: HC