Laos has the worst roads anywhere, blacktop that has disintegrated and left the base of chunky rocks. Mongolia has the best roads, which are just hard-packed wheel tracks across the steppe, but they are designed according to where the horses first travelled and make no concessions to the limited hill-climbing power of bicycles. Tibet has some beautiful new bitumen roads courtesy of the Han Chinese, engineering marvels which switch their way up and down climbs of a couple of thousand metres, but the best places are accessed on tracks built for, and maintained by, logging trucks. Vietnam has some good paved road in the Northwest between Hanoi and Dien Bien Phu but the road from there to Sapa is dirt. Indonesia build their remote roads with only tar and no gravel, making for beautifully slick bike track. Nepal roads are OK but busy, but off the main road the best thing is to leave your bike behind and walk.