If you're intending to travel between Sichuan and Yunnan, there's another less popular route that passes through Derong. For the most part its a quiet, peaceful road with a few sections of dirt no more than 100 meters. The road from Xiengcheng to Derong is notable for the long stretches of time between vehicles. Its 290km, and doable in two days.
I was advised by 4 other cyclists that the direct road from Shangrila to Xiangcheng is a terrible mess- swarms of trucks, traffic, dusk, mud, rocks, etc.. - after traveling through a similar mess in Wolong, I gambled with Derong and it paid off quite nicely.