Cycling from Chengdu to Lhasa by the national highway G318, the total distance is about 2154km. And there are two mountains over 5000 meters and ten mountains with altitude of over 4000 meters to cross over by highway. The bike ride on this route will take over 20 days to finish, and need to climb one mountain by highway in every 2 days. Difficult as it is, the road abounds with extraordinary natural scenery from plain to plateau, from forest to snow-capped mountain, and deep gorge, etc. The raging torrent from Qinghai-Tibet plateau will accompany you all the way.
https://www.tibettravel.org/tibet-tour/chengdu-to-lhasa-biking.html