Passo del Mortirolo by bike: guide to one of the Alps' hardest climbs

The Passo del Mortirolo, in Valtellina, is considered by many to be one of the hardest climbs in Europe — not so much for its length as for a gradient that stays almost constantly above 10%, without the recovery sections found on other great alpine passes. It became a cycling legend largely thanks to the Giro d'Italia, which has climbed it several times over the years, cementing it as one of the symbolic places of climbing on a bike.

The classic side from Mazzo di Valtellina

The best-known and hardest side starts in Mazzo di Valtellina, at around 552 meters of elevation, and climbs to the 1,852-meter pass, for a total elevation gain of around 1,300 meters over just over 12 km. The average gradient is around 10.5%, with sections that, according to several sources, exceed 20% at their steepest, particularly in the middle part of the climb where the road narrows through the woods.

How to tackle it without burning out in the first km

The most common mistake on this climb is going out hard on the first switchbacks, where the gradient is already severe, and arriving with nothing left for the middle section — the truly decisive part. It's better to set a sustainable pace from the start, using an easy gear (if your drivetrain has a wide-range cassette, this is the moment to use it) and treating the climb as a series of small sections to manage one at a time rather than one continuous effort.

When to go and what to bring

Practical tips for climb day

Start with full bottles: water stops along the climb aren't a given, especially through the toughest wooded sections. Check your drivetrain carefully before setting off, because a gear that slips at the wrong moment on an 18-20% gradient can force you to stop somewhere restarting is far from easy. If this is your first big alpine climb, it's also worth reading our guide on getting ready for your first gran fondo to plan your training in the weeks beforehand.

Recommended products

Tackling a climb this demanding calls for the right gear: a wide-range cassette for steep climbs if you're considering a drivetrain upgrade, an insulated bike bottle to keep water cool even on the hottest sections, and a packable windproof vest to always carry for the descent.

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