Kum by bike: 8.6 km at 11% to the top of Zasavje

Kum is the highest peak in Zasavje, 1,220 m above the coal-mining towns of the Sava valley, and its road is short, steep and relentless. Our track climbs 952 m in 8.6 km from the river at Škofja Riža, an average of 11.1%, and not one kilometre of it drops below 8.7%. The Trbovlje tourist board compares the ascent with Vršič and puts it among the top five road and mountain-bike goals in Slovenia. Here is how the climb is built, how to survive an hour at 11%, and what to expect from the gravel at the top.

The climb: nine kilometres with no rest

The tourist board describes the route from Trbovlje railway station: across the Sava, up the main road to Dobovec, then follow the signs for Kum past the old Lontovž ski area. It counts about 9 km of steep asphalt and then 2 km of macadam to the top. Our track starts on the far bank of the river, at 249 m, so it skips the flat run through town. Otherwise it is the same road.

• Škofja Riža to Dobovec: straight into it. There is no gentle approach. The first kilometre is 10.6% and the second is 12.9%, the steepest full kilometre on the track. You reach Dobovec, at about 480 m, after roughly 2 km. The village has a church and a shop, and the tourist board suggests a stop here.
• Dobovec to Lontovž: the long middle. From Dobovec the road climbs through the woods at a steady 10–11%. Kilometre five, at 8.7%, is the closest thing to a break on the whole climb, and it is still steeper than most passes in the Alps. By 6 km you are above 900 m.
• Lontovž to the top: steeper and rougher. Past the abandoned ski slopes at Lontovž the gradient climbs again: 11.4%, 11.9%, then 12.5% for the last stretch. The tourist board says the last two kilometres are unpaved. Our track ends just below the summit at 1,203 m, by the mountain lodge and the 17th-century church of St Neža.

How to ride an hour at 11%

For a fit amateur Kum takes somewhere between 45 minutes and well over an hour. On a climb this steep your speed is so low that there is no free speed from drafting or aerodynamics. It is just you, your weight and your gears.

• Gear for 12%, not for the average. A 34×32 or 34×34 is not too much. It keeps your cadence above 60 so your legs don't seize halfway up. Our guide to gearing for climbing shows how to work out what you need.
• Start below threshold and stay there. Aim for 85–90% of FTP from the river. The second kilometre will push you above that whatever you do, so ride it seated and steady, and don't try to win it. Pacing a climb with power explains why even beats heroic.
• Mix seated and standing. An hour seated at 11% loads your lower back. Stand for 20–30 pedal strokes every few minutes to change the muscles that are working, then sit back down. Standing power covers how to do it without spiking your effort.
• Treat the gravel with respect. Going up, stay seated on the loose sections so the rear wheel keeps grip. Coming down, the gravel and the gradient together make this a slow descent. Brake early and keep it gentle, and run 28 mm tyres or wider if you have them.

Why Kum matters to Zasavje

Kum rises across the Sava from Trbovlje, and the land around it is protected as the Kum Landscape Park, whose highest point is the summit itself. Locals call the peak Zasavski Triglav, the Triglav of Zasavje, and the tourist board says it is the highest peak in both Zasavje and Dolenjska. It actually has two tops. The 17th-century church of St Neža, with its free-standing bell tower, sits on the lower one, with the mountain lodge just below. The old RTV transmitter stands on the slightly higher one. On a clear day the tourist board promises views as far as Triglav, Pohorje and Snežnik.

For cyclists the attraction is simple: few roads in the country climb this steeply for this long.

When to go, and what to watch for

• Season. The road is low enough to ride from spring to late autumn, but the top is nearly 1,000 m above the valley and noticeably colder. The gravel stretch can be muddy after rain. Take a jacket for the descent.
• Surface. Expect asphalt to Lontovž and gravel above it. A road bike manages if you ride carefully. If the gravel is badly washed out, walking the last few hundred metres is no disgrace.
• Hikers. Several marked trails reach the top, including a short one from Lontovž, so expect walkers on the upper road and around the lodge.
• The descent. Over 11% on average with tight bends through the woods, this is a descent for brakes, not for speed. On hydraulic discs, brake in pulses so the rotors don't overheat. Descending faster and safer has the technique.
• Make it a day. Kum is short, so most riders combine it with the Sava valley roads. The tourist board's own loop starts and ends at Trbovlje station, which makes the train a sensible way to arrive.

Ride it in Moveee Indoor

The route on this page is the real road from the Sava to the top of Kum, with its height at every point. In Moveee Indoor your smart trainer reproduces that gradient as you ride, and the world around you is built from the map of the actual place: the river, the village of Dobovec, the woods above it. Kum is ideal indoors because the hard part is not the view, it is holding a steady effort on a gradient that never lets up. That is exactly what a trainer teaches. You find out which gear you need and what power you can hold for an hour at 11% before you are on the real thing.

Ride it once to set a baseline, then again after a block of threshold work, and compare the power and the time. Prefer your own device? Download the GPX above and load it into any app that rides GPX files.

The short version

8.6 km at 11.1% from the Sava to 1,203 m, with no kilometre under 8.7% and gravel at the top. Fit the lowest gear you own, start below threshold and stay seated on the loose stuff. Come down slowly, and ride it on the trainer first so the second kilometre doesn't surprise you.