Took the challenge during Ironman Hawaii week to cycle one of the toughest climbs in the world from the ocean to the top of Mauna Kea over 4200m of elevation and up to 20% steep with a killer gravel section, by far the hardest ride I did, had to change to 30mm CX tires on my BMC Roadmachine for the 8km lava sand and gravel section before the top but managed without a single meter walking. Spectacular views but only recommended with support car. Had no energy left to go down